Lanthanoid-Anilato Complexes and Lattices ^†

Abstract

In this review, we describe all the structurally characterized complexes containing lanthanoids (Ln, including La and group 3 metals: Y and Lu) and any anilato-type ligand (3,6-disubstituted-2,5-dihydroxy-1,4-benzoquinone dianion = C₆O₄X₂²⁻). We present all the anilato-Ln compounds including those where, besides the anilato-type ligand, there is one or more coligands or solvent molecules coordinated to the lanthanoid ions. We show the different structural types observed in these compounds: from discrete monomers, dimers and tetramers to extended 1D, 2D and 3D lattices with different topologies. We also revise the magnetic properties of these Ln-anilato compounds, including single-molecule magnet (SMM) and single-ion magnet (SIM) behaviours. Finally, we show the luminescent and electrochemical properties of some of them, their gas/solvent adsorption/absorption and exchange capacity and the attempts to prepare them as thin films.

1. Introduction

The field of coordination polymers (CPs) and metal organic frameworks (MOFs) with lanthanoids (Ln) is gaining interest in this decade since they may show gas and solvent exchange and adsorption/absorption and present interesting magnetic and luminescent properties and can, therefore, be used to prepare optical and magnetic sensors of gases, contaminants and different chemical species [1,2,3].

Among the many different ligands that can be used to construct these CPs and MOFs, anilato-type ligands (3,6-disubstituted-2,5-dihydroxy-1,4-benzoquinone dianion = C₆O₄X₂²⁻, Scheme 1a) are becoming very popular since these ligands present some interesting properties: (i) They show different coordination modes as: monodentate (1kO), bidentate (1k²O,O′), bis-bidentate (1k²O,O′;2k²O″,O‴), monodentate-bidentate (1kO;2k²O′,O″) or even more complex coordination modes such as (1k²O,O′;2k²O″,O‴;3kO″) (Scheme 1c–f) [4,5]. (ii) They can act as linear bridges connecting two metal atoms (Scheme 1a) to generate many different coordination polymers [4]. (iii) They couple (antiferro)magnetically the metal centers when they are transition metal ions and the coupling can be modulated by changing X [6]. (iv) They provide a good magnetic isolation when bridging lanthanoids (as a result of the negligible overlap with the 4f orbitals), giving rise to single-molecule and single-ion magnet behaviours (SMM and SIM). (v) They can be reduced by one or two electrons to their semiquinone and cathecolate forms (Scheme 1b), resulting in an increase in the magnetic coupling and ordering temperatures [7]. (vi) They are topologically equivalent to the well-known oxalato ligand (C₂O₄²⁻) and they are able to form similar monomeric complexes [8,9] as well as extended 1D, 2D and 3D lattices although with much larger cavities and channels [4,5,10,11].

Although anilato and its derivatives (Scheme 1a) have been combined with transition metals since the 1950s [12], the use of lanthanoids with anilato ligands was not developed until the 21st century. Surprisingly, there are only three reports in the 20th century. The first one, published in 1983 by Raymon et al. [13] describes a compound with Pr(III) and chloranilate (X = Cl). The second one, published in 1987 by Robl et al. [14] presents a couple of Y(III) compounds with chloranilate and bromanilate (X = Br). The third report was published in 1996 by Robson, Abrahams et al. [15] and contains a Ce(III) compound with dhbq²⁻ (X = H).

The first complete and systematic study was performed by Robson, Abrahams et al. in 2002 [16]. In this seminal article, the authors prepared and structurally characterized a total of 19 Ln-anilato compounds (and one with Sc) using dhbq²⁻ (X = H) and chloranilato (X = Cl). Since then, almost 150 Ln-anilato compounds have been prepared, as we will show in this review.

The structures and properties of homometallic coordination polymers prepared with anilato ligands and transition metals (and even p- and s-block metals) were revised in a very complete study in 2002 by Kitagawa and Kawata [4]. More recently, in 2017, Mercuri et al. [17] performed a complete revision, focusing on the magnetic and conducting properties, of homo- and heterometallic complexes and coordination polymers with anilato and transition metals. Finally, we have very recently revised the heterometallic anilato-based 2D and 3D lattices with transition metals [18].

Surprisingly, as far as we know, no revision of the almost 150 prepared lanthanoid-anilato compounds has been published to date. Therefore, here we revise all the structurally characterized Ln-anilato compounds. We will show the different anilato-type ligands used (Scheme 1a) and their magnetic and luminescent properties. We will also show the gas and solvent adsorption/absorption and the solvent exchange capacity of some of them as well as the attempts to reduce the anilato bridge in some dimers. Finally, we will show the delamination of some of the layered lattices into thin films with promising properties.

This review is organized into seven different sections: In Section 1, we introduce the anilato-type ligands and their properties as well as their capacity to coordinate in a bis-bidentate way and to act as bridges connecting lanthanoid ions in coordination complexes and polymers. In Section 2, we will show and describe all the reported structures: (i) discrete monomers, dimers and tetramers; (ii) zigzag and ladder-type chains; (iii) hexagonal, rectangular and square layers; and (iv) 3D structures. In Section 3, we will show the magnetic properties of some of these compounds, focusing on their (in most cases, field-induced) single-molecule magnet (SMM) and single-ion magnet (SIM) behaviours. In Section 4, we will show their optical properties, including luminescence in the visible and NIR regions. In Section 5, we will show the porosity, gas and solvent adsorption/absorption and solvent exchange capacity of some of the layered Ln-anilato materials. In Section 6, we will show their redox properties and, finally, in Section 7, we will show how it is possible to easily delaminate some of the layered compounds to prepare thin films with nanometric thickness.

In order to classify all the reported Ln-anilato-based compounds, we will present them in different tables grouped by type of structure and dimensionality (Tables 1 to 7), by anilato derivative ligand (Tables 8 to 12) and by Ln(III) ion (Tables 13 to 27). We hope that these tables will help in finding any compound and all those with the same Ln(III) ion, the same ligand, or the same (or related) structure.

2. Structural Classification

2.1. Discrete (0D) Complexes

As can be seen in Table 1, there are 33 reported discrete complexes containing lanthanoids and anilato ligands. There are thirty dimers (2-31), two monomers (1 and 33) and one tetramer (32). The only two reported monomers are: [Lu(C₆O₄Cl₂)(H₂O)₄][Lu(C₆O₄Cl₂)₂(H₂O)₄]·≈4H₂O (33) [16] and [Co(Cp)₂][Dy(Tp)₂(C₆O₄Cl₂)] (1) (Tp^- = hydrotris(pyrazolyl)borate = HB(pz)₃) [19]. Compound 1 is an anionic Dy(III) complex with a terminal bidentate chloranilate and two tridentate Tp^- ligands (Figure 1a) with [Co(Cp)₂]⁺ as counter-cations, whereas compound 33 contains the anionic [Lu(C₆O₄Cl₂)₂(H₂O)₄]⁻ monomer with two terminal chloranilato ligands (Figure 1b). The counter cation of this monomeric anion is a cationic chain that will be described below. Although there are many known dimers, there is only one reported tetramer: [[((Tp)(MeOH)Y)₂(μ-B(OMe)₄)]₂(μ-C₆O₄(CH₃)₂)₂]Cl₂ (32) [20]. This compound is a Y(III) square complex with two bis-bidentante bridging methyl-anilato ligands (X = CH₃) forming two parallel sides and two B(OMe)₄ units forming the two other sides. The coordination sphere of the Y(III) ions is completed with one Tp^- ligand and one MeOH molecule (Figure 1c).

Compounds [Ln₂(C₆O₄H₂)(thf)₆Cl₄] with Ln = Dy (2) and Y (3) [21] constitute two unusual dimers. They are isostructural and contain a bis-bidentate bridging dhbq²⁻ ligand (X = H) connecting the two Ln(III) ions. Each Ln ion completes its unusual pentagonal bipyramidal coordination geometry with two Cl and three thf coligands (Figure 2a).

Dimers [(LnTp)₂(C₆O₄X₂)]·G with Ln/X/G = Dy/Cl/2CH₂Cl₂ (4-6), Y/Cl/2CH₂Cl₂ (7-8), Y/Cl/2Me₂CO (9), Y/H/- (10), Y/CH₃/1.2CH₂Cl₂ (11) and Y/CH₃/4.5MeOH (12) [19,20,22] are isostructural and contain a bridging anilato ligand (with X = H, Cl, or CH₃) connecting two Y(III) or Dy(III) ions. The octacoordination of the Ln(III) ions (with TDD-8 or SAPR-8 geometries, Table 1) is completed by two tridentate Tp^- ligands in all cases (Figure 2b). Dimers [(LnTp)₂(C₆O₄X₂)]·G with Ln/X/G = Dy/Br/2CH₂Cl₂ (18), Dy/F/H₂O (19), Y/F/H₂O (20) and Y/Br/2CH₂Cl₂ (21) [23] and [(LnTp)₂(C₆O₄Cl₂)]·2CH₂Cl₂ with Ln = Er (22), Ho (23), Tb (24-25), Gd (26-27) and Y (28-29) [19,22,24,25] are very similar to dimers 4-12. They also contain a bis-bidentate anilate bridging ligand (chloranilato in all of them) connecting the two Ln(III) ions and Tp^- as capping ligands (Figure 2b) and they all show a TDD-8 coordination geometry (Table 1).

Table 1. Discrete (1-33) and 1D (33 and 34) Ln-anilato complexes.

#	CCDC	Structure	Ln	X	Geometry a	L b	Disposition	Reference
1	PIQFUT	Monomer	Dy	Cl	SAPR-8	Tp-	33	[19]
2	DEHQUF	Dimer	Dy	H	PBPY-7	thf/Cl-	030/101	[21]
3	DEHRAM	Dimer	Y	H	PBPY-7	thf/Cl-	030/101	[21]
4	DEKTOF	Dimer	Dy	Cl	TDD-8	Tp-		[20]
5	DEKTOF01	Dimer	Dy	Cl	TDD-8	Tp-		[22]
6	DEKTOF02	Dimer	Dy	Cl	TDD-8	Tp-		[19]
7	DEKTUL	Dimer	Y	Cl	TDD-8	Tp-		[20]
8	DEKTUL01	Dimer	Y	Cl	TDD-8	Tp-		[22]
9	DEKVAT	Dimer	Y	Cl	TDD-8	Tp-		[20]
10	DEKVEX	Dimer	Y	H	SAPR-8	Tp-		[20]
11	DEKVIB	Dimer	Y	CH3	SAPR-8	Tp-		[20]
12	DEKVOH	Dimer	Y	CH3	TDD-8	Tp-		[20]
13	EDEZAR	Dimer	Gd	NO2	CSAPR-9	H2O	032	[26]
14	EDEZEV	Dimer	Tb	NO2	CSAPR-9	H2O	032	[26]
15	EDEZIZ	Dimer	Dy	NO2	CSAPR-9	H2O	032	[26]
16	EDEZOF	Dimer	Ho	NO2	CSAPR-9	H2O	032	[26]
17	EDEZUL	Dimer	Sm	NO2	CSAPR-9	H2O	032	[26]
18	JOQSEQ	Dimer	Dy	Br	TDD-8	Tp-		[23]
19	JOQSIU	Dimer	Dy	F	SAPR-8	Tp-	33	[23]
20	JOQSOA	Dimer	Y	F	SAPR-8	Tp-	33	[23]
21	JOQSUG	Dimer	Y	Br	TDD-8	Tp-		[23]
22	KOZBEJ	Dimer	Er	Cl	TDD-8	Tp-		[24]
23	KOZBIN	Dimer	Ho	Cl	TDD-8	Tp-		[24]
24	LEPNIG	Dimer	Tb	Cl	TDD-8	Tp-		[22]
25	LEPNIG01	Dimer	Tb	Cl	TDD-8	Tp-		[24]
26	LEPNOM	Dimer	Gd	Cl	TDD-8	Tp-		[22]
27	LEPNOM01	Dimer	Gd	Cl	TDD-8	Tp-		[19]
28	OBIBEH	Dimer	Yb	Cl	TDD-8	Tp-		[25]
29	OBIBEH01	Dimer	Yb	Cl	TDD-8	Tp-		[24]
30	NOQBUT	Dimer-zz	Eu	Cl/CN	CSAPR-9	H2O	032	[27]
31	NOQGEI	Dimer-zz	Eu/Dy c	Cl/CN	CSAPR-9	H2O	032	[27]
32	DEKVUN	Tetramer	Y	CH3	TDD-8	Tp-/(MeO)4B/MeOH		[20]
33	MIZZUQ	1D + mon	Lu	Cl	TDD-8	H2O		[16]
34	NIGNID	1D-ladder	Er1/Er2	Cl	BTPR-8/BTPR-8	hmpa		[28]

(^a) The geometry was determined with the program SHAPE [29,30,31,32,33,34,35,36]. SAPR-8 = square antiprism, PBPY-7 = pentagonal bipyramid, TDD-8 = triangular dodecahedron, CSAPR-9 = capped square antiprism, BTPR-8 = biaugmented trigonal prism; (^b) Tp^- = HB(pz)₃⁻ = hydrotris(pyrazolyl)borate, thf = tetrahydrofurane, dmso = dimethyl sulfoxide, hmpa = hexamethylphosphoramide; (^c) Eu (98%)/Dy (2%).

Table 1. Discrete (1-33) and 1D (33 and 34) Ln-anilato complexes.

#	CCDC	Structure	Ln	X	Geometry a	L b	Disposition	Reference
1	PIQFUT	Monomer	Dy	Cl	SAPR-8	Tp-	33	[19]
2	DEHQUF	Dimer	Dy	H	PBPY-7	thf/Cl-	030/101	[21]
3	DEHRAM	Dimer	Y	H	PBPY-7	thf/Cl-	030/101	[21]
4	DEKTOF	Dimer	Dy	Cl	TDD-8	Tp-		[20]
5	DEKTOF01	Dimer	Dy	Cl	TDD-8	Tp-		[22]
6	DEKTOF02	Dimer	Dy	Cl	TDD-8	Tp-		[19]
7	DEKTUL	Dimer	Y	Cl	TDD-8	Tp-		[20]
8	DEKTUL01	Dimer	Y	Cl	TDD-8	Tp-		[22]
9	DEKVAT	Dimer	Y	Cl	TDD-8	Tp-		[20]
10	DEKVEX	Dimer	Y	H	SAPR-8	Tp-		[20]
11	DEKVIB	Dimer	Y	CH3	SAPR-8	Tp-		[20]
12	DEKVOH	Dimer	Y	CH3	TDD-8	Tp-		[20]
13	EDEZAR	Dimer	Gd	NO2	CSAPR-9	H2O	032	[26]
14	EDEZEV	Dimer	Tb	NO2	CSAPR-9	H2O	032	[26]
15	EDEZIZ	Dimer	Dy	NO2	CSAPR-9	H2O	032	[26]
16	EDEZOF	Dimer	Ho	NO2	CSAPR-9	H2O	032	[26]
17	EDEZUL	Dimer	Sm	NO2	CSAPR-9	H2O	032	[26]
18	JOQSEQ	Dimer	Dy	Br	TDD-8	Tp-		[23]
19	JOQSIU	Dimer	Dy	F	SAPR-8	Tp-	33	[23]
20	JOQSOA	Dimer	Y	F	SAPR-8	Tp-	33	[23]
21	JOQSUG	Dimer	Y	Br	TDD-8	Tp-		[23]
22	KOZBEJ	Dimer	Er	Cl	TDD-8	Tp-		[24]
23	KOZBIN	Dimer	Ho	Cl	TDD-8	Tp-		[24]
24	LEPNIG	Dimer	Tb	Cl	TDD-8	Tp-		[22]
25	LEPNIG01	Dimer	Tb	Cl	TDD-8	Tp-		[24]
26	LEPNOM	Dimer	Gd	Cl	TDD-8	Tp-		[22]
27	LEPNOM01	Dimer	Gd	Cl	TDD-8	Tp-		[19]
28	OBIBEH	Dimer	Yb	Cl	TDD-8	Tp-		[25]
29	OBIBEH01	Dimer	Yb	Cl	TDD-8	Tp-		[24]
30	NOQBUT	Dimer-zz	Eu	Cl/CN	CSAPR-9	H2O	032	[27]
31	NOQGEI	Dimer-zz	Eu/Dy c	Cl/CN	CSAPR-9	H2O	032	[27]
32	DEKVUN	Tetramer	Y	CH3	TDD-8	Tp-/(MeO)4B/MeOH		[20]
33	MIZZUQ	1D + mon	Lu	Cl	TDD-8	H2O		[16]
34	NIGNID	1D-ladder	Er1/Er2	Cl	BTPR-8/BTPR-8	hmpa		[28]

(^a) The geometry was determined with the program SHAPE [29,30,31,32,33,34,35,36]. SAPR-8 = square antiprism, PBPY-7 = pentagonal bipyramid, TDD-8 = triangular dodecahedron, CSAPR-9 = capped square antiprism, BTPR-8 = biaugmented trigonal prism; (^b) Tp^- = HB(pz)₃⁻ = hydrotris(pyrazolyl)borate, thf = tetrahydrofurane, dmso = dimethyl sulfoxide, hmpa = hexamethylphosphoramide; (^c) Eu (98%)/Dy (2%).

In contrast, dimers [Ln₂(C₆O₄(NO₂))₃(H₂O)₁₀]·6H₂O with Ln = Gd (13), Tb (14), Dy (15), Ho (16) and Sm (17) [26] and [Ln₂(C₆O₄(CN)Cl)₃(H₂O)₁₀]·6H₂O with Ln = Eu (30) and Eu_0.98/Dy_0.02 (31) [27] contain three anilato ligands: a bridging bis-bidentante one (as observed in all the other dimers) and a terminal bidentate one on each Ln center (in contrast with the previously described dimers). The remaining five coordination positions are occupied by water molecules. The coordination geometry is CSAPR-9 in all cases (Table 1). In dimers 13-17, the two Ln(III) ions and the centers of the three anilato ligands are aligned, resulting in “linear dimers” (Figure 2c), whereas in dimers 30 and 31, the center of the terminal anilato ligands is not aligned with the Ln···Ln axis, resulting in “zigzag dimers” (Figure 2d).

2.2. One Dimensional (1D) Lattices

Table 1 also shows the only two known 1D polymers containing Ln and anilato-type ligands: [Lu(C₆O₄Cl₂)(H₂O)₄][Lu(C₆O₄Cl₂)₂(H₂O)₄]·≈ 4H₂O (33) [16] and [Er₂(C₆O₄Cl₂)₃(hmpa)(H₂O)₃]·H₂O (34) (hmpa = hexamethylphosphoramide) [28]. The chains present in compound 33 are regular cationic zigzag chains formulated as [Lu(C₆O₄Cl₂)(H₂O)₄]⁺ formed by bis-bidentate bridging chloranilato ligands connecting Lu(III) ions (Figure 3a). These chains are similar to those observed with transition metals [4] although now, the Lu(III) ions have four extra coordinated water molecules, in contrast with the transition metals, that only have two. Interestingly, the counter-anions of these cationic chains are also unique since they are the anionic monomers [Lu(C₆O₄Cl₂)₂(H₂O)₄]⁻ described above (Figure 1b). Although the full crystal structure was not reported, Robson et al. also prepared the Yb(III) derivative of compound 33 [16].

The other chain compound, [Er₂(C₆O₄Cl₂)₃(hmpa)(H₂O)₃]·H₂O (34), is an example of the important role played by the size and shape of the coordinating solvents (L) in determining the final structure and the dimensionality [28]. In this compound, the presence of a very bulky coordinating solvent (hexamethylphosphoramide) precludes the growth of the coordination polymer in two or three dimensions, in contrast with the observed behaviour in other related polymers with smaller coordinating solvent molecules (see below). Compound 33, the only known example of Ln-anilato compound with a ladder chain structure, presents a (3,4) topology where both the side rail and the rungs are formed by bridging bis-bidentate chloranilato ligands (Figure 3b). There are two unique Er(III) ions, both with an unusual biaugmented trigonal prism geometry (BTPR-8) due to the steric hindrance of the bulky coordinated hexamethylphosphoramide molecule [28].

2.3. Two-Dimensional (2D) Lattices

Two-dimensional lattices are, by far, the most common ones in the Ln-anilato family of compounds, with more than one hundred known examples (Tables 2 to 6). In order to rationalize these 2D lattices, we have classified them according to their topology and shape of the rings forming the layers. As can be seen in Tables 2 to 6, the most recurrent ones are the hexagonal 3,6-gon and square 4,4-gon topologies.

The 3,6-gon topology is, by far, the most abundant one, with more than 90 reported examples (Tables 2 to 5). In this topology, each Ln(III) is connected to three other Ln(III) ions through anilato bridges giving rise to regular (Figure 4a and Table 2) or distorted (Figure 4b and Table 3) hexagonal rings with the typical honey comb hexagonal structure. In some of these lattices the hexagons are so distorted that they look like rectangles (with two Ln-Ln-Ln angles close to 180°). These rectangular six-membered rings may adopt a brick-wall structure (Figure 4c and Table 4) or a herringbone one (Figure 4d and Table 5).

The 4,4-gon topology (Figure 4e) is observed in a total of twenty compounds (130-149, Table 6). In these 2D lattices, each Ln(III) is connected to four Ln(III) ions by anilato bridges giving rise to square rings that form a chessboard square structure.

Only three compounds show different 2D lattices: [La₂(C₆O₄Cl₂)₃(H₂O)₆]·≈7H₂O (129) [16], that shows a 3,4 topology (see below) and [Ln₂(C₆O₄ClCN)₃(dmso)₆]·nH₂O with Ln/n = Er/0 (150) and Dy/7 (151), that show a (3,4)+(3,8) topology (Figure 4f and Table 6) [37,38].

As observed by Robson, Abrahams et al. in their seminal work in 2002 [16], the distortions of the hexagonal rings are due to the differences in the spatial orientations of the anilato ligands around the Ln(III) ions, which, in turn, depend on the coordination geometry and on the position occupied of the two or three coordinated solvent molecules (L). As we will see below, the size of the Ln(III) ion and the size and shape of the coordinated solvent molecules also play a key role in the final structure. The different orientations result in different angles between the anilato rings and the average plane of the layer. Thus, in the regular hexagons, the anilato rings appear tilted ca. 45° with respect to the layer (Figure 5a), whereas in the distorted hexagons, there are two possible dispositions: four anilato with their rings almost parallel to the layer (face-on, FO) and two rings almost perpendicular to it (edge-on, EO) (Figure 5b) or the opposite (i.e., 2 FO + 4 EO, Figure 5c). In the rectangular layers, there are two FO and four EO ones (Figure 5d). As can be seen in Figure 5, the diagonals of the regular hexagons are around 16.6 Å, whereas in the distorted hexagons, the diagonals are of ca. 15, 17 and 19 Å (depending on the distortions). Finally, the rectangular rings show two large distances (of ca. 18–20 Å) and a much shorter one (of ca. 7 Å).

Two important aspects of these 2D lattice are: (i) the planarity (or lack of planarity) of the four-, six-, or eight-membered rings and (ii) the relative disposition of two consecutive layers along the direction perpendicular to the layers (eclipsed or alternated). The eclipsed disposition implies the formation of channels (hexagonal or rectangular) that may contain crystallization solvent molecules that might be removed and/or exchanged, as we will show below.

2.3.1. Two-Dimensional Regular Hexagonal Lattices

The most common 2D structural type is the hexagonal honey comb lattice (Table 2 and Figure 4a), where each Ln(III) ion is connected to three other through bis-bidentate anilato bridges, also observed with transition metals [39,40]. The main difference is that due to their higher ionic radii, the coordination numbers of the Ln(III) ions are higher (usually eight or nine) and there are two or three coordination positions occupied by other ligands (L). These additional coligands are, in most cases, H₂O or a solvent with a high capacity to coordinate Ln(III) ions such as dimethyl sulfoxide (dmso), dimethylformamide (dmf), or dimethylacetamide (dma) [41,42]. The most important consequences of this increase in the coordination number are (i) the lack of planarity of the hexagonal rings (and, therefore, of the honey comb layers) and/or (ii) the presence of distortions in the hexagonal rings.

The lack of planarity was observed in the series of compounds reported by Robson, Abrahams et al. with dhbq²⁻ (X = H) formulated as [Ln₂(dhbq)₃(H₂O)₆]·18H₂O with Ln(III) = La (36), Gd (37), Yb (38), Lu (39), Y (40) and Ce (42) [15,16], later enlarged by Ohkoshi et al. with Ho(III) (35) [43], by Chainok et al. with Er (41) [44] and recently completed by us [45] with Pr (43), Nd (44), Sm (45), Eu (46), Tb (47), Dy (48) and Tm (49) (Table 2). In this series of isostructural compounds, the hexagons are very regular but they are not planar. They show three equal Ln···Ln distances of ca. 16.6 Å along the diagonals of the hexagons (Figure 5a) and show a chair conformation (Figure 6a) with Ln-Ln-Ln angles (°) close to those of a tetrahedron (Table 2).

As noted by Robson et al. [16], this lack of planarity is due to the coordination of three water molecules that occupy one triangular face of the tricapped trigonal prismatic (TCTPR-9) coordination geometry of the Ln(III) ions (Figure 6b). We call this distribution as 300 in Table 2 to indicate that there are three solvent molecules on the upper triangular face of the trigonal prism (3--) and no solvent molecules on the central (-0-) nor lower (--0) positions (of course, the 300 disposition is equivalent to the 003 one since the trigonal prism can be upside down). Each of the three dhbq²⁻ ligands occupies a central capping position (-1-) and one vertex of the lower triangular face (--1) (therefore, each anilato is coordinated at the 011 positions). This disposition results in a propeller-like orientation of the anilato ligands, giving rise to corrugated hexagonal layers (Figure 6c). These layers are packed in an alternated way, preventing the formation of hexagonal channels perpendicular to the layer. Interestingly, the water molecules in this layered structure form a Ln₂(H₂O)₁₈ cage with six coordinated water molecules and twelve crystallization ones (Figure 6d). These cages connect two nonconsecutive layers and cross the hexagonal hole of the layer in between them. As we will show below, the 12 crystallization water molecules can be easily removed in a reversible way and even exchanged with other different solvents such as MeOH, EtOH, dmf, HCOOH and CH₃COOH.

Table 2. Ln-anilato compounds with regular hexagonal 2D structures.

#	CCDC	Ln	X	Geometry a	L b	Disposition	α (°) c	Pk d	Reference
35	KUYKIZ	Ho	H	TCTPR-9	H2O	300	107.7	AL	[43]
36	MIZXAU	La	H	TCTPR-9	H2O	300	107.2	AL	[16]
37	MIZXEY	Gd	H	TCTPR-9	H2O	300	107.6	AL	[16]
38	MIZXIC	Yb	H	TCTPR-9	H2O	300	107.8	AL	[16]
39	MIZXOI	Lu	H	TCTPR-9	H2O	300	107.7	AL	[16]
40	MIZXUO	Y	H	TCTPR-9	H2O	300	107.7	AL	[16]
41	PIVKAJ	Er	H	TCTPR-9	H2O	300	107.7	AL	[44]
42	ZOTTAD	Ce	H	TCTPR-9	H2O	300	107.3	AL	[15]
43	1944109	Pr	H	TCTPR-9	H2O	300	107.3	AL	[45]
44	1944110	Nd	H	TCTPR-9	H2O	300	107.4	AL	[45]
45	1944111	Sm	H	TCTPR-9	H2O	300	107.4	AL	[45]
46	1944112	Eu	H	TCTPR-9	H2O	300	107.5	AL	[45]
47	1944113	Tb	H	TCTPR-9	H2O	300	107.6	AL	[45]
48	1944114	Dy	H	TCTPR-9	H2O	300	107.6	AL	[45]
49	1944117	Tm	H	TCTPR-9	H2O	300	107.7	AL	[45]
50	DIFLEM	Ce	Cl/CN	CSAPR-9	dmf	021	99.6	AL	[46]
51	WOTWIO	Dy	Cl/CN	CSAPR-9	dmf	021	102.0	AL	[47]
52	WOTWOU	Ho	Cl/CN	CSAPR-9	dmf	021	102.2	AL	[47]
53	XIKNOX	Nd	Cl/CN	CSAPR-9	dmf	021	101.3	AL	[48]
54	XIKPAL	Er	Cl/CN	CSAPR-9	dmf	021	103.0	AL	[48]
55	XOYTEN	Dy	Cl/CN	CSAPR-9	dmf	021	101.8	AL	[38]
56	NIGNUP	Er	Cl	CSAPR-9	fma	021	127.2	AL	[28]

(^a) The geometry was determined with the program SHAPE [29,30,31,32,33,34,35,36]. TCTPR-9 = tri-capped trigonal prism, CSAPR-9 = capped square antiprism; (^b) dmf = dimethylformamide, fma = formamide; (^c) largest Ln-Ln-Ln angle in the hexagon. (^d) packing: EC = eclipsed, AL = alternated.

Table 2. Ln-anilato compounds with regular hexagonal 2D structures.

#	CCDC	Ln	X	Geometry a	L b	Disposition	α (°) c	Pk d	Reference
35	KUYKIZ	Ho	H	TCTPR-9	H2O	300	107.7	AL	[43]
36	MIZXAU	La	H	TCTPR-9	H2O	300	107.2	AL	[16]
37	MIZXEY	Gd	H	TCTPR-9	H2O	300	107.6	AL	[16]
38	MIZXIC	Yb	H	TCTPR-9	H2O	300	107.8	AL	[16]
39	MIZXOI	Lu	H	TCTPR-9	H2O	300	107.7	AL	[16]
40	MIZXUO	Y	H	TCTPR-9	H2O	300	107.7	AL	[16]
41	PIVKAJ	Er	H	TCTPR-9	H2O	300	107.7	AL	[44]
42	ZOTTAD	Ce	H	TCTPR-9	H2O	300	107.3	AL	[15]
43	1944109	Pr	H	TCTPR-9	H2O	300	107.3	AL	[45]
44	1944110	Nd	H	TCTPR-9	H2O	300	107.4	AL	[45]
45	1944111	Sm	H	TCTPR-9	H2O	300	107.4	AL	[45]
46	1944112	Eu	H	TCTPR-9	H2O	300	107.5	AL	[45]
47	1944113	Tb	H	TCTPR-9	H2O	300	107.6	AL	[45]
48	1944114	Dy	H	TCTPR-9	H2O	300	107.6	AL	[45]
49	1944117	Tm	H	TCTPR-9	H2O	300	107.7	AL	[45]
50	DIFLEM	Ce	Cl/CN	CSAPR-9	dmf	021	99.6	AL	[46]
51	WOTWIO	Dy	Cl/CN	CSAPR-9	dmf	021	102.0	AL	[47]
52	WOTWOU	Ho	Cl/CN	CSAPR-9	dmf	021	102.2	AL	[47]
53	XIKNOX	Nd	Cl/CN	CSAPR-9	dmf	021	101.3	AL	[48]
54	XIKPAL	Er	Cl/CN	CSAPR-9	dmf	021	103.0	AL	[48]
55	XOYTEN	Dy	Cl/CN	CSAPR-9	dmf	021	101.8	AL	[38]
56	NIGNUP	Er	Cl	CSAPR-9	fma	021	127.2	AL	[28]

(^a) The geometry was determined with the program SHAPE [29,30,31,32,33,34,35,36]. TCTPR-9 = tri-capped trigonal prism, CSAPR-9 = capped square antiprism; (^b) dmf = dimethylformamide, fma = formamide; (^c) largest Ln-Ln-Ln angle in the hexagon. (^d) packing: EC = eclipsed, AL = alternated.

A similar structure with regular hexagonal rings is also observed in the series of compounds [Ln₂(C₆O₄ClCN)₃(dmf)₆]·nG with G = H₂O and CH₂Cl₂ and Ln = Ce (50), Dy (51), Ho (52), Nd (53), Er (54) and Dy (55). This series contain the asymmetric chlorocyananilato (X = Cl and CN) ligand and dimethylformamide (dmf) instead of water as additional coligand [38,46,47,48].

The hexagonal rings are even more bent than in the dhbq²⁻ series (Figure 7a), resulting in smaller Ln-Ln-Ln angles (around 100°, see Table 2) and in more corrugated layers (Figure 7b). The lack of planarity in this series is also attributed to the spatial disposition of the chlorocyananilato ligands around the Ln(III) ions, although now, the coordination geometry is a distorted capped square antiprism (CSAPR-9, Figure 7c) with the solvent molecules occupying two positions of the capped square face and one in the other square face, (021 in our notation, Table 2). One of the anilato ligands occupies the capped position and one position in the upper square face (110), a second anilato ligand occupies one position on each of the two square faces (011) and the third anilato ligand occupies two positions in the lower square face (002) (Figure 7c). As in the previous series, the layers are packed in an alternated way.

Finally, there is an additional example of regular hexagonal rings with chloranilato, Er(III) and formamide (fma) as coligand: [Er₂(C₆O₄Cl₂)₃(fma)₆]·4fma·2H₂O (56) (Figure 8a) [28]. The coordination geometry around the Er(III) ion is also a distorted CSAPR-9 with the solvent molecules showing a 021 disposition (Figure 8b), although now they are not located on the same triangular face, as observed in the [Ln₂(C₆O₄ClCN)₃(dmf)₆]·nG series (Figure 7c). The three anilato ligands show the same distribution (110, 011 and 002) although, of course, cannot occupy the same positions. Interestingly, as a result of this change in the disposition of the solvent molecules and the anilato ligands, the hexagonal rings are now almost planar (Figure 8c), the Ln-Ln-Ln angles are close to the ideal value of 120° (Table 2) and the layers are much flatter (Figure 8d) although are also packed in an alternated way.

2.3.2. Two-Dimensional Distorted Hexagonal Lattices

The second effect of the increase in the coordination number of the Ln(III) ions is the distortion observed in the hexagonal rings (Figure 4b). The main consequence of this distortion implies an increase of two opposite Ln-Ln-Ln angles, which are now in the range of 133–150° (Table 3). These distortions were already observed by Robson, Abrahams et al. in the series of chloranilato-based compounds formulated as [Ln₂(C₆O₄Cl₂)₃(H₂O)₆]·nH₂O with Ln(III) = Pr (58), Nd (59), Tb (60), Ce (61 and 62), Y (63), Gd (64) and Eu (65) [15,16], later enlarged with a EtOH solvate of the Gd(III) derivative: [Gd₂(C₆O₄Cl₂)₃(H₂O)₆]·2EtOH (57) by Zucchi et al. [49] and recently completed by us [28,45] with Ln(III) = Er (66), La (67), Sm (68), Dy (69) and Ho (70) (Table 3). Interestingly, in this series of compounds, Robson et al. found different structural types (phases) depending on the size of the Ln(III) ion and the number of crystallization water molecules (n):

Type I structure corresponds to a coordination number of ten and is only observed for the largest ion, La(III), with n = 7. This phase is not a (3,6)-phase, but a double (3,4) one, and will be described below (compound 128).

Type II structure is formed when the coordination number is nine. It is observed for most of the intermediate Ln(III) ions. There are three different type II structures:

Type IIa is originally found for the large lanthanoids, i.e., Ce (61 and 62), Pr (58), Nd (59) and, surprisingly, for the smaller Tb (60) ion (Table 3). This structure has ≈ 12 crystallization water molecules and shows distorted hexagonal rings with two FO and four EO anilato rings (Figure 9a). The Ln(III) ions present a TCTPR-9 geometry with the coordinated water molecules occupying one vertex of each of the triangular faces and one of the capping positions (disposition 111) (Figure 9b). The three anilato ligands show dispositions of the type 200, 011 and 011. Interestingly, the Ce(III) derivative shows a single-crystal to single-crystal phase transition from a monoclinic C2/m phase (61) to a triclinic P-1 one (62) upon losing a small amount of crystallization water [16]. The monoclinic phase also presents a similar distorted hexagonal lattice and a similar TCTPR-9 coordination geometry with a 111 disposition of the coordinated water molecules (Table 3). Interestingly, the Gd(III) derivative has also been obtained as both, the monoclinic C2/m phase in a EtOH solvate (57) [49] and as the triclinic P-1 phase with water as crystallization solvent (64) [16].

Type IIb structure was originally obtained for Y (63), Gd (64) and Eu (65) with n ≈ 10 (Table 3) and is very similar to type IIa. The main difference is the presence of four FO and two EO anilato rings in the distorted hexagonal cavities (Figure 9c) instead of two FO and four EO, as in type IIa. This difference is due to the different positions of the solvent molecules around the Ln(III) ions that now are located on the triangular faces (two in one face and one in the other in a 201 disposition, compared to the 111 disposition found in phase IIa). The anilato ligands show dispositions of the type 110, 011 and 011 (Figure 9d).

Finally, Robson et al. also noted that there is a third type II phase that they called Type IIc that had only been observed in less hydrated compounds such as [Pr₂(C₆O₄Cl₂)₃(EtOH)₆]·2EtOH (96) [13] and [Y₂(C₆O₄Cl₂)₃(H₂O)₆]·≈6H₂O (97) [14]. This phase has later been observed in other compounds with small lanthanoids and chloranilato or bromanilato as ligands (see Table 4). It shows very distorted hexagonal cavities that can be considered as rectangles and will be described in the next section with the rectangular 3,6 lattices.

As already noted by Robson et al. [16], the number of crystallization water molecules in these series is not easy to determine. Furthermore, the exact number may depend on the storage conditions of the single crystals. In order to shed some light on this matter, we have recently completed the [Ln₂(C₆O₄Cl₂)₃(H₂O)₆]·nH₂O series and performed a study of the crystal structures of all the members of the series [45]. This study showed that if the single crystals are taken directly from the mother liquor and covered with grease to prevent any solvent loss, then the series [Ln₂(C₆O₄Cl₂)₃(H₂O)₆]·nH₂O presents up to four different water contents: (i) n = 14, for the four largest ions (La to Nd); (ii) n = 12, for the intermediate ion (Sm to Ho); (iii) n = 10, for Er and (iii) n = 8, for the two smallest ions (Yb and Tm). Compounds with n = 14 and 12 (from La to Ho) are isostructural and their structure corresponds to the structural type IIa described by Robson et al. [16]. The only known example with n = 10 (Ln = Er) shows different unit cell parameters and, therefore, is a different crystalline phase (not a solvate). This phase corresponds to the structural type IIb described by Robson et al. [16]. Finally, for n = 8 (Ln = Tm and Yb), the structure shows more important changes since now, the coordinated water molecules occupy different positions (two on one triangular face and one on the other, with a 201 disposition) and the hexagonal rings are so distorted that they look like rectangles. This phase corresponds to the ones reported by Robl for [Y₂(C₆O₄X₂)₃(H₂O)₆]·nH₂O with X/n = Cl/6.6 (97) and Br/6 (101) [14] and will be described with the rectangular phases in the next section.

Table 3. Reported Ln-anilato compounds with distorted hexagonal 2D structures.

	CCDC	Ln	X	Geometry a	L b	Disposition	Type	α (°) c	Pk d	Reference
57	GEQBAH e	Gd	Cl	TCTPR-9	H2O	111	IIa	138.0	AL	[49]
58	MIZYID	Pr	Cl	TCTPR-9	H2O	111	IIa	134.9	AL	[16]
59	MIZYOJ	Nd	Cl	TCTPR-9	H2O		IIa	–	AL	[16]
60	MIZYUP	Tb	Cl	TCTPR-9	H2O	111	IIa	135.8	AL	[16]
61	MIZZAW e	Ce	Cl	TCTPR-9	H2O	111	IIa	133.7	AL	[16]
62	MIZZAW01	Ce	Cl	TCTPR-9	H2O	111	IIa	134.6	AL	[16]
63	MIZZEA	Y	Cl	TCTPR-9	H2O	111	IIa	136.1	AL	[16]
64	MIZZIE	Gd	Cl	TCTPR-9	H2O	111	IIb	136.2	AL	[16]
65	MIZZOK	Eu	Cl	TCTPR-9	H2O		IIb	–	AL	[16]
66	NIGNEZ	Er	Cl	TCTPR-9	H2O	201	IIb	136.6	AL	[28]
67	1944118	La	Cl	TCTPR-9	H2O	111	IIa	133.4	AL	[45]
68	1944120	Sm	Cl	TCTPR-9	H2O	111	IIa	135.0	AL	[45]
69	1944123	Dy	Cl	TCTPR-9	H2O	111	IIa	135.7	AL	[45]
70	1944124	Ho	Cl	TCTPR-9	H2O	111	IIa	136.0	AL	[45]
71	XAWZUT	Er	Br	TCTPR-9	H2O	111	IIa	138.4	AL	[50]
72	1565271	La	Br	TCTPR-9	H2O	111	IIa	135.0	AL	[45]
73	1565272	Ce	Br	TCTPR-9	H2O	111	IIa	136.2	AL	[45]
74	1565273	Pr	Br	TCTPR-9	H2O	111	IIa	137.8	AL	[45]
75	1565274	Nd	Br	TCTPR-9	H2O	111	IIa	136.9	AL	[45]
76	1565275	Sm	Br	TCTPR-9	H2O	111	IIa	137.7	AL	[45]
77	1565276	Eu	Br	TCTPR-9	H2O	111	IIa	137.4	AL	[45]
78	1565277	Gd	Br	TCTPR-9	H2O	111	IIa	137.7	AL	[45]
79	1565278	Tb	Br	TCTPR-9	H2O	111	IIa	138.3	AL	[45]
80	1565279	Dy	Br	TCTPR-9	H2O	111	IIa	138.1	AL	[45]
81	1565280	Ho	Br	TCTPR-9	H2O	111	IIa	138.3	AL	[45]
82	NIDFOY	Tb	Br	TDD-8	dmso	trans	IIb	141.0	AL	[51]
83	NIDFUE	Dy	Br	TDD-8	dmso	trans	IIb	140.7	AL	[51]
84	NIDGAL	Ho	Br	TDD-8	dmso	trans	IIb	141.4	AL	[51]
85	XAXBAC	Er	Br	TDD-8	dmso	trans	IIb	140.7	AL	[50]
86	NIDGEP	Yb	Br	TDD-8	dmso	trans	IIb	141.3	AL	[51]
87	DIFLUC	Yb	Cl/CN	TDD-8	dmso	trans	IIb	150.0	AL	[46]
88	POMTUJ	Yb	Cl/CN	TDD-8	dmso	trans	IIb	144.8	AL	[37]
89	POMVAR	Yb/Er	Cl/CN	TDD-8	dmso	trans	IIb	145.2	AL	[37]
90	NIGQIG	Er	Cl	TDD-8	dmso	trans	IIb	141.0	AL	[28]
91	NIGNOJ	Er	Cl	TDD-8	dmso	trans	IIb	142.3	AL	[28]
92	KUVBIP	La	t-Bu	TDD-8	dma	cis	IIb	138.3	EC	[52]
93	KUVBOV	Pr	t-Bu	TDD-8	dma	cis	IIb	136.6	EC	[52]
94	KUVBUB	Nd	t-Bu	TDD-8	dma	cis	IIb	135.8	EC	[52]
95	LEBGEG	Gd	H	SAPR-8	thf/Cl-	20	–	140.8	AL	[53]

(^a) The geometry was determined with the program SHAPE [29,30,31,32,33,34,35,36]. TCTPR-9 = tricapped trigonal prism, TDD-8 = triangular dodecahedron, SAPR-8 = square antiprism; (^b) dmso = dimethyl sulfoxide, dma = dimethylacetamide, thf = tetrahydrofurane; (^c) largest Ln-Ln-Ln angle in the hexagon; (^d) packing: EC = eclipsed, AL = alternated. (^e) monoclinic C2/m phase.

Table 3. Reported Ln-anilato compounds with distorted hexagonal 2D structures.

	CCDC	Ln	X	Geometry a	L b	Disposition	Type	α (°) c	Pk d	Reference
57	GEQBAH e	Gd	Cl	TCTPR-9	H2O	111	IIa	138.0	AL	[49]
58	MIZYID	Pr	Cl	TCTPR-9	H2O	111	IIa	134.9	AL	[16]
59	MIZYOJ	Nd	Cl	TCTPR-9	H2O		IIa	–	AL	[16]
60	MIZYUP	Tb	Cl	TCTPR-9	H2O	111	IIa	135.8	AL	[16]
61	MIZZAW e	Ce	Cl	TCTPR-9	H2O	111	IIa	133.7	AL	[16]
62	MIZZAW01	Ce	Cl	TCTPR-9	H2O	111	IIa	134.6	AL	[16]
63	MIZZEA	Y	Cl	TCTPR-9	H2O	111	IIa	136.1	AL	[16]
64	MIZZIE	Gd	Cl	TCTPR-9	H2O	111	IIb	136.2	AL	[16]
65	MIZZOK	Eu	Cl	TCTPR-9	H2O		IIb	–	AL	[16]
66	NIGNEZ	Er	Cl	TCTPR-9	H2O	201	IIb	136.6	AL	[28]
67	1944118	La	Cl	TCTPR-9	H2O	111	IIa	133.4	AL	[45]
68	1944120	Sm	Cl	TCTPR-9	H2O	111	IIa	135.0	AL	[45]
69	1944123	Dy	Cl	TCTPR-9	H2O	111	IIa	135.7	AL	[45]
70	1944124	Ho	Cl	TCTPR-9	H2O	111	IIa	136.0	AL	[45]
71	XAWZUT	Er	Br	TCTPR-9	H2O	111	IIa	138.4	AL	[50]
72	1565271	La	Br	TCTPR-9	H2O	111	IIa	135.0	AL	[45]
73	1565272	Ce	Br	TCTPR-9	H2O	111	IIa	136.2	AL	[45]
74	1565273	Pr	Br	TCTPR-9	H2O	111	IIa	137.8	AL	[45]
75	1565274	Nd	Br	TCTPR-9	H2O	111	IIa	136.9	AL	[45]
76	1565275	Sm	Br	TCTPR-9	H2O	111	IIa	137.7	AL	[45]
77	1565276	Eu	Br	TCTPR-9	H2O	111	IIa	137.4	AL	[45]
78	1565277	Gd	Br	TCTPR-9	H2O	111	IIa	137.7	AL	[45]
79	1565278	Tb	Br	TCTPR-9	H2O	111	IIa	138.3	AL	[45]
80	1565279	Dy	Br	TCTPR-9	H2O	111	IIa	138.1	AL	[45]
81	1565280	Ho	Br	TCTPR-9	H2O	111	IIa	138.3	AL	[45]
82	NIDFOY	Tb	Br	TDD-8	dmso	trans	IIb	141.0	AL	[51]
83	NIDFUE	Dy	Br	TDD-8	dmso	trans	IIb	140.7	AL	[51]
84	NIDGAL	Ho	Br	TDD-8	dmso	trans	IIb	141.4	AL	[51]
85	XAXBAC	Er	Br	TDD-8	dmso	trans	IIb	140.7	AL	[50]
86	NIDGEP	Yb	Br	TDD-8	dmso	trans	IIb	141.3	AL	[51]
87	DIFLUC	Yb	Cl/CN	TDD-8	dmso	trans	IIb	150.0	AL	[46]
88	POMTUJ	Yb	Cl/CN	TDD-8	dmso	trans	IIb	144.8	AL	[37]
89	POMVAR	Yb/Er	Cl/CN	TDD-8	dmso	trans	IIb	145.2	AL	[37]
90	NIGQIG	Er	Cl	TDD-8	dmso	trans	IIb	141.0	AL	[28]
91	NIGNOJ	Er	Cl	TDD-8	dmso	trans	IIb	142.3	AL	[28]
92	KUVBIP	La	t-Bu	TDD-8	dma	cis	IIb	138.3	EC	[52]
93	KUVBOV	Pr	t-Bu	TDD-8	dma	cis	IIb	136.6	EC	[52]
94	KUVBUB	Nd	t-Bu	TDD-8	dma	cis	IIb	135.8	EC	[52]
95	LEBGEG	Gd	H	SAPR-8	thf/Cl-	20	–	140.8	AL	[53]

(^a) The geometry was determined with the program SHAPE [29,30,31,32,33,34,35,36]. TCTPR-9 = tricapped trigonal prism, TDD-8 = triangular dodecahedron, SAPR-8 = square antiprism; (^b) dmso = dimethyl sulfoxide, dma = dimethylacetamide, thf = tetrahydrofurane; (^c) largest Ln-Ln-Ln angle in the hexagon; (^d) packing: EC = eclipsed, AL = alternated. (^e) monoclinic C2/m phase.

Given the important structural changes (from regular hexagons to distorted ones and even rectangles) observed when the ligand dhbq²⁻ (X = H) is replaced by chloranilato (X = Cl), we decided to synthesize and structurally characterize the same series with bromanilato (X = Br). The complete bromanilato series can be formulated as: [Ln₂(C₆O₄Br₂)₃(H₂O)₆]·nH₂O with Ln/n = La/9 (72), Ce/8 (73), Pr/11 (74), Nd/7 (75), Sm/10 (76), Eu/6 (77), Gd/8 (78), Tb/10 (79), Dy/8 (80), Ho/10 (81), Er/7 (71), Tm/5.5 (102) and Yb/3.5 (103) (Table 3 and Table 4) [45]. Although the general trend is that the number of crystallization water molecules decreases as the size of the Ln(III) decreases, there are some exceptions. These exceptions can be explained by the fact that the solvent molecules occupy the interlayer space and the inner space in the distorted hexagonal cavities and the exact number can change easily (as observed in the series with chloranilato). Despite the many different water contents, we only observe three different crystal phases along the series. The two largest ions (La and Ce) show a structure very similar to type IIa observed for chloranilato, with the same distorted hexagonal rings (Figure 10a) and with the same 111 disposition of the coordinated water molecules and 200, 011 and 011 dispositions for the anilato ligands (Figure 10b).

The intermediate Ln(III) ions (from Pr to Er) show a second type of unit cell parameters and a structure very similar to that of La and Ce (type IIa structure with distorted hexagonal rings, Figure 10c) and the same distribution of the coordinated water molecules around the Ln(III) ion (Figure 10d). Finally, the two smallest Ln(III) ions (Tm and Yb) present a completely different structure with less crystallization water molecules and rectangular rings, similar to those observed with chloranilato (Table 4). These rectangular lattices will be described in the next section.

A third series showing a distorted honey comb structure with four FO and two EO anilato ligands (type IIb) was obtained for the small lanthanoids (from Tb to Yb) using dimethyl sulfoxide (dmso) as solvent: [Ln₂(C₆O₄Br₂)₃(dmso)₄]·2dmso·2H₂O with Ln = Tb (82), Dy (83), Ho (84), Er (85) and Yb (86) (Figure 11a and Table 3) [50,51]. In this series, the Ln(III) ions are octacoordinated due to the large size of the coordinated solvent (dmso) and small size of the Ln(III) ions. This role of the size of the Ln(III) ion is clearly demonstrated by the fact that the large lanthanoids (from La to Gd) coordinate a third dmso molecule and form rectangular layers that will be described in the next section. The coordination geometry in compounds 82-86 is a triangular dodecahedron (TDD-8) and the two dmso molecules are coordinated in trans positions with O-Ln-O bond angles of ca. 150°, in order to reduce the steric hindrance of the bulky dmso molecules (Figure 11b). A similar structure with the same coordination geometry around the Ln(III) ions is also observed in three closely related compounds prepared with the asymmetric ligand chlorocyananilato (X = Cl and CN) and Yb(III) or a 1:1 mixture of Yb/Er: [Yb₂(C₆O₄ClCN)₃(dmso)₄]·2H₂O (87) [46], [Yb₂(C₆O₄ClCN)₃(dmso)₄]·dmso (88) and [YbEr(C₆O₄ClCN)₃(dmso)₄]·dmso (89) [37] and in two related compounds with chloranilato and Er(III) with dmso and dimethylacetamide (dma) as solvents: [Er₂(C₆O₄Cl₂)₃(dmso)₄]·2dmso·2H₂O (90) [28] and [Er₂(C₆O₄Cl₂)₃(dma)₄] (91) (Table 3) [28].

There are three very recently reported distorted hexagonal lattices prepared with tert-butyl-anilato (X = t-Bu) and dma, formulated as: [Ln₂(C₆O₄(t-Bu)₂)₃(dma)₄] with Ln = La (92), Pr (93) and Nd (94) (Figure 11c and Table 3) [52]. The coordination geometry is also a TDD-8 but in contrast to compounds 82-91, in 92-94 the two dma ligands occupy cis positions with O-Ln-O angles of ca. 83° (Figure 11d). The smaller steric hindrance of dma compared to dmso may be at the origin of this different disposition. A second difference is the distortion of the hexagonal cavities, much more pronounced in compounds 92-94 (Figure 11c) probably due to the steric effect of the bulky tert-butyl groups in the anilato ligands.

There is a final example formulated as [Gd(dhbq)Cl(thf)₂] (95) that shows a quite original distorted hexagonal lattice where one of the anilato bridges is replaced by a double Cl^- one [53]. This change implies that two of the six sides of the hexagons are much shorter than the other four (4.49 vs. 8.63 Å and 8.64 Å, Figure 12a). In this compound, each Gd(III) ion is coordinated to two bis-bidentate bridging dhbq²⁻ ligands, two bridging Cl^- ligands and two thf molecules (Figure 12b) in a very distorted square antiprism geometry (SAPR-8, Table 3). The two Cl^- ligands occupy cis positions on the same square face of the square antiprism (20), whereas the thf molecules are located one on each square face (11) and the two dhbq²⁻ ligands are located with 11 and 02 dispositions (Figure 12b). This spatial orientation gives rise to very distorted but almost planar hexagonal rings with the coordinated thf molecules pointing almost perpendicular to the ring plane (Figure 12c).

2.3.3. 2D Rectangular Lattices

When the distortion of the hexagons becomes more important, the largest Ln-Ln-Ln angles increase and reach values in the range ca. 160-170°. The hexagonal cavities look like rectangles, although keeping the same 3,6 topology (Figure 4c,d). As can be seen in Table 4 and Table 5, these large distortions are common and, in fact, were already observed in [Pr₂(C₆O₄Cl₂)₃(EtOH)₆]·2EtOH (96), the first Ln-anilato compound reported in 1983 by Raymond et al. [13].

The rectangular rings may adopt two possible structures: (i) a brick-wall one where the long axis of all the rectangles are parallel (Figure 4c) and (ii) spike-like or herringbone, where the long axis of the rectangles of neighbouring rows are almost orthogonal (Figure 4d).

Table 4. Reported Ln-anilato compounds with a rectangular 2D structure and a brick-wall structure.

#	CCDC	Ln	X	Geometry a	L b	Disposition	α (°)c	Pk d	Reference
96	CAZZAE	Pr	Cl	TCTPR-9	EtOH	201	162.1	AL	[13]
97	GASMUI	Y	Cl	TCTPR-9	H2O	201	169.9	AL	[14]
98	JOGJAT	Er	Cl	CSAPR-9	H2O	030	166.4	AL	[54]
99	1944126	Tm	Cl	TCTPR-9	H2O	210	171.5	AL	[45]
100	1944127	Yb	Cl	TCTPR-9	H2O	210	171.3	AL	[45]
101	GASMOC	Y	Br	TCTPR-9	H2O	210	169.5	AL	[14]
102	1565282	Tm	Br	TCTPR-9	H2O	210	169.0	AL	[45]
103	LUTRIE	Yb	Br	TCTPR-9	H2O	210	168.8	AL	[55]
104	DIFLOW	Pr	Cl/CN	CSAPR-9	dmso	030	164.0	EC	[46]
105	NOQGAE	Eu/Dy	Cl/CN	CSAPR-9	dmso	030	163.2	EC	[27]
106	WOTWUA	Ce	Cl/CN	CSAPR-9	dmso	030	164.4	EC	[47]
107	WOTXAH	Nd	Cl/CN	CSAPR-9	dmso	030	163.8	EC	[47]
108	XOYTUD	Dy	Cl/CN	CSAPR-9	dmso	030	162.6	EC	[38]
109	WOTWEK	Nd	Cl/CN	CSAPR-9	dmf	012	157.9	EC	[47]
110	GEPZUY	Eu	Cl	TCTPR-9	bipym/H2O	110/100	172.7	EC	[49]
111	QOVJUJ	Yb1/Yb2	Cl/CN	TDD-8/TDD-8	dmso/dobdc2−	trans	144.4/165.1	AL	[56]
112	QOVJOD	Yb	Cl/CN	TDD-8	dmso/F4bdc2−	–	158.4	AL	[56]

(^a) The geometry was determined with the program SHAPE [29,30,31,32,33,34,35,36]. TCTPR-9 = tri-capped trigonal prism, CSAPR-9 = capped square antiprism, TDD-8 = triangular dodecahedron; (^b) dmso = dimthylsulfoxide, dmf = dimethylformamide, bipym = 2,2′-bipyrimidine, H₂dobdc = 2,5-dihydroxybenzene-1,4-dicarboxylic acid, H₂F₄bdc = 2,3,5,6-tetrafluorobenzene-1,4-dicarboxylic acid; (^c) largest Ln-Ln-Ln angle in the hexagon; (^d) packing: EC = eclipsed, AL = alternated.

Table 4. Reported Ln-anilato compounds with a rectangular 2D structure and a brick-wall structure.

#	CCDC	Ln	X	Geometry a	L b	Disposition	α (°)c	Pk d	Reference
96	CAZZAE	Pr	Cl	TCTPR-9	EtOH	201	162.1	AL	[13]
97	GASMUI	Y	Cl	TCTPR-9	H2O	201	169.9	AL	[14]
98	JOGJAT	Er	Cl	CSAPR-9	H2O	030	166.4	AL	[54]
99	1944126	Tm	Cl	TCTPR-9	H2O	210	171.5	AL	[45]
100	1944127	Yb	Cl	TCTPR-9	H2O	210	171.3	AL	[45]
101	GASMOC	Y	Br	TCTPR-9	H2O	210	169.5	AL	[14]
102	1565282	Tm	Br	TCTPR-9	H2O	210	169.0	AL	[45]
103	LUTRIE	Yb	Br	TCTPR-9	H2O	210	168.8	AL	[55]
104	DIFLOW	Pr	Cl/CN	CSAPR-9	dmso	030	164.0	EC	[46]
105	NOQGAE	Eu/Dy	Cl/CN	CSAPR-9	dmso	030	163.2	EC	[27]
106	WOTWUA	Ce	Cl/CN	CSAPR-9	dmso	030	164.4	EC	[47]
107	WOTXAH	Nd	Cl/CN	CSAPR-9	dmso	030	163.8	EC	[47]
108	XOYTUD	Dy	Cl/CN	CSAPR-9	dmso	030	162.6	EC	[38]
109	WOTWEK	Nd	Cl/CN	CSAPR-9	dmf	012	157.9	EC	[47]
110	GEPZUY	Eu	Cl	TCTPR-9	bipym/H2O	110/100	172.7	EC	[49]
111	QOVJUJ	Yb1/Yb2	Cl/CN	TDD-8/TDD-8	dmso/dobdc2−	trans	144.4/165.1	AL	[56]
112	QOVJOD	Yb	Cl/CN	TDD-8	dmso/F4bdc2−	–	158.4	AL	[56]

(^a) The geometry was determined with the program SHAPE [29,30,31,32,33,34,35,36]. TCTPR-9 = tri-capped trigonal prism, CSAPR-9 = capped square antiprism, TDD-8 = triangular dodecahedron; (^b) dmso = dimthylsulfoxide, dmf = dimethylformamide, bipym = 2,2′-bipyrimidine, H₂dobdc = 2,5-dihydroxybenzene-1,4-dicarboxylic acid, H₂F₄bdc = 2,3,5,6-tetrafluorobenzene-1,4-dicarboxylic acid; (^c) largest Ln-Ln-Ln angle in the hexagon; (^d) packing: EC = eclipsed, AL = alternated.

The brick-wall structure has been observed in five compounds with chloranilato: [Pr₂(C₆O₄Cl₂)₃(EtOH)₆]·2EtOH (96) [13], [Ln₂(C₆O₄Cl₂)₃(H₂O)₆]·nH₂O with Ln/n = Y/6.6 (97), Tm/8 (99) and Yb/8 (100) [14,45] and [Er₂(C₆O₄Cl₂)₃(H₂O)₆]·2H₂O·1.5CH₃COCH₃ (98) [54] as well as in three related compounds with bromanilato: [Y₂(C₆O₄Br₂)₃(H₂O)₆]·6H₂O (101) [14], [Ln₂(C₆O₄Br₂)₃(H₂O)₆]·nH₂O with Ln/n = Tm/5.5 (102) [45] and Yb/3.5 (103) [55] (Table 4). Except for compound 98, that shows a capped square antiprism (CSAPR-9) geometry, the coordination geometry around the Ln(III) ions is tricapped trigonal prism (TCTPR-9) with the coordinated water molecules in 210 disposition and the anilato ligands in positions 110, 011 and 002 (Figure 13a). Compound 96 has EtOH instead of water and shows a 201 disposition of the solvent molecules (with the anilato ligands in 110, 011 and 011 positions (Figure 13b). This difference may be due to the larger size of the EtOH molecules compared to H₂O. As mentioned above, compound 98 is the only one in these series with a CSAPR-9. The water molecules are coordinated in 030 disposition and the anilato ligands in 110, 002 and 002 (Figure 13c). This surprising result might be due to the templating effect of the NMe₄⁺ or NBu₄⁺ cations used during the synthesis of compound 98, in contrast to that of the NEt₄⁺ cations, that produce anionic 3D lattices, as we will see below [54].

A second series of compounds showing the brick-wall structure is the series prepared with the asymmetric chlorocyananilato ligand (X = Cl and CN) with dmso as solvent formulated as [Ln₂(C₆O₄ClCN)₃(dmso)₆]·G with Ln = Pr (104) [46], Eu/Dy (105) [27], Ce (106) [47], Nd (107) [47] and Dy (108) [38]. In this series, the Ln(III) ions show a CSAPR-9 geometry with the three dmso molecules occupying three vertices of the capped square face (030) and the chlorocyananilato ligands in 110, 002 and 002 dispositions (Figure 14a). Interestingly, if we replace the dmso by dmf in the Nd(III) derivative, the obtained compound, formulated as [Nd₂(C₆O₄ClCN)₃(dmf)₆] (109) [47] also shows the brick-wall structure in the layers and a CSAPR-9 geometry, but the disposition of the solvent molecules (dmf) is different since now they occupy one position on the capped square face and two on the bottom one (012). The chlorocyananilato ligands show 110, 011 and 011 dispositions (Figure 14b).

There are three more compounds with a brick-wall lattice and different coligands such as 2,2′-bipyrimidine (bipym): [Eu₂(C₆O₄Cl₂)₃(bipym)₂]·4EtOH (110) [49], the dianion of 2,5-dihydroxybenzene-1,4-dicarboxylic acid (H₂dobdc): [Yb₄(C₆O₄(CN)Cl)₅(dobdc)(dmso)₁₀]·2dmso (111) [56] and the dianion of 2,3,5,6-tetrafluorobenzene-1,4-dicarboxylic acid (H₂F₄bdc): [Yb₂(C₆O₄(CN)Cl)₂(F₄bdc)(dmso)₆] (112) [56]. Compound 110 presents a TCTPR-9 geometry with 110 and 100 dispositions of the bidentate bipym and H₂O coligands, respectively. The three chloranilato ligands show 110, 011 and 002 dispositions (Figure 14c).

Compound 111 shows two independent Yb ions, both with TDD-8 geometry, although with different coordination environments: Yb1 is coordinated to three bidentate anilato ligand and two trans dmso molecules (Figure 15a), whereas Yb2 is coordinated to two bidentate anilato ligands, three dmso molecules and one dobdc²⁻ monodentate ligand (Figure 15b).

The layers in compound 111 are formed by distorted hexagons with six anilato ligands (with a maximum Ln-Ln-Ln angle of 144.4°) alternating with rectangles containing four anilato and two dobdc²⁻ ligands (with a maximum Ln-Ln-Ln angle of 165.1º). The directions of both largest Ln-Ln-Ln angles are parallel, resulting in a brick-wall structure of the distorted hexagons and the rectangles [56]. Finally compound 112 also has a TDD-8 geometry with two bidentante anilato ligands, three dmso molecules and one monodentate F₄bdc²⁻ ligand (Figure 15c), very similar to Yb2 in 111. The rectangles in the layers in compound 112 contain four anilato and two F₄bdc²⁻ ligands [56].

The other structural type found in the rectangular cavities is the so-called herringbone or spike-like structure (Figure 4d). In this structure, the rectangles are also arranged in parallel rows but the rectangles of consecutive rows are tilted ca. 90°. This structure has been found in a total of fifteen compounds with lanthanoids and anilato ligands (Table 5). In all cases, the coordination geometry around the Ln(III) ion is capped square antiprism (CSAPR-9) and the three solvent molecules are located in three vertices of the capped face (030 disposition) (Figure 15d). With chloranilato, this herringbone structure has only been found in three compounds: two with water, [Gd₂(C₆O₄Cl₂)₃(H₂O)₆]·2bipym·6H₂O (113) [49] and [Ce₂(C₆O₄Cl₂)₃(H₂O)₆]·2H₂O·3C₃H₆O (114) [54] and one with dmf: [Er₂(C₆O₄Cl₂)₃(dmf)₆] (115) [28]. In contrast, with bromanilato, the herringbone structure is more common and has been found in eight compounds with dmso: [Ln₂(C₆O₄Br₂)₃(dmso)₆]·2dmso [51], with Ln = La (116), Ce (117), Pr (118), Nd (119), Sm (120), Eu (121), Gd (122) and also in the Dy-doped Eu derivative: [Dy_0.04Eu_1.96(C₆O₄Br₂)₃(dmso)₆]·2dmso (123) [27]. As mentioned above, this series shows the key role that plays the size of the Ln(III) ion on the coordination number, coordination geometry and final structure. Thus, for the smaller Ln(III) ions (from Tb to Yb, 82–86), the coordination number is eight, the geometry is TDD-8 and the structure is a distorted hexagonal lattice (Table 3), whereas for the larger Ln(III) ions (from La to Gd, 116-122), the coordination number is nine, the geometry is CSAPR-9 and the structure is a rectangular herringbone lattice [27].

The herringbone structure has also been found in four compounds with dmf, two with bromanilato: [Ln₂(C₆O₄Br₂)₃(dmf)₆]; Ln = Er (124) [50] and Dy (125) [55] and two with the asymmetric chlorocyananilato ligand: [Ln₂(C₆O₄(CN)Cl)₃(dmf)₆]; Ln = Pr (126) [46] and Yb (127) [48].

Table 5. Reported Ln-anilato compounds with a rectangular 2D structure and a herringbone structure.

#	CCDC	Ln	X	Geometry a	L b	Disposition	α (°) c	Pk d	Reference
113	GEQBEL	Gd	Cl	CSAPR-9	H2O	030	159.9	EC	[49]
114	JOGHAR	Ce	Cl	CSAPR-9	H2O	030	164.5	AL	[54]
115	NIGPAX	Er	Cl	CSAPR-9	dmf	030	160.3	EC	[28]
116	NIDLIY	La	Br	CSAPR-9	dmso	030	165.5	EC	[51]
117	NIDLOE	Ce	Br	CSAPR-9	dmso	030	165.4	EC	[51]
118	NIDLUK	Pr	Br	CSAPR-9	dmso	030	165.5	EC	[51]
119	NIDMAR	Nd	Br	CSAPR-9	dmso	030	164.0	EC	[51]
120	NIDMEV	Sm	Br	CSAPR-9	dmso	030	164.0	EC	[51]
121	NIDFEO	Eu	Br	CSAPR-9	dmso	030	163.8	EC	[51]
122	NIDFIS	Gd	Br	CSAPR-9	dmso	030	163.7	EC	[51]
123	NOQBON	Eu/Dy e	Br	CSAPR-9	dmso	030	163.9	EC	[27]
124	XAXBEG	Er	Br	CSAPR-9	dmf	030	159.0	EC	[50]
125	LUTROK	Dy	Br	CSAPR-9	dmf	030	158.9	EC	[55]
126	DIFLIQ	Pr	Cl/CN	CSAPR-9	dmf	030	170.7	EC	[46]
127	XIKNUD	Yb	Cl/CN	CSAPR-9	dmf	030	167.0	EC	[48]

(^a) The geometry was determined with the program SHAPE [29,30,31,32,33,34,35,36]. CSAPR-9 = capped square antiprism; (^b) dmf = dimethylformamide, dmso = dimethyl sulfoxide, (^c) largest Ln-Ln-Ln angle in the hexagon; (^d) packing: EC = eclipsed, AL = alternated; (^e) Eu (98%)/Dy (2%).

Table 5. Reported Ln-anilato compounds with a rectangular 2D structure and a herringbone structure.

#	CCDC	Ln	X	Geometry a	L b	Disposition	α (°) c	Pk d	Reference
113	GEQBEL	Gd	Cl	CSAPR-9	H2O	030	159.9	EC	[49]
114	JOGHAR	Ce	Cl	CSAPR-9	H2O	030	164.5	AL	[54]
115	NIGPAX	Er	Cl	CSAPR-9	dmf	030	160.3	EC	[28]
116	NIDLIY	La	Br	CSAPR-9	dmso	030	165.5	EC	[51]
117	NIDLOE	Ce	Br	CSAPR-9	dmso	030	165.4	EC	[51]
118	NIDLUK	Pr	Br	CSAPR-9	dmso	030	165.5	EC	[51]
119	NIDMAR	Nd	Br	CSAPR-9	dmso	030	164.0	EC	[51]
120	NIDMEV	Sm	Br	CSAPR-9	dmso	030	164.0	EC	[51]
121	NIDFEO	Eu	Br	CSAPR-9	dmso	030	163.8	EC	[51]
122	NIDFIS	Gd	Br	CSAPR-9	dmso	030	163.7	EC	[51]
123	NOQBON	Eu/Dy e	Br	CSAPR-9	dmso	030	163.9	EC	[27]
124	XAXBEG	Er	Br	CSAPR-9	dmf	030	159.0	EC	[50]
125	LUTROK	Dy	Br	CSAPR-9	dmf	030	158.9	EC	[55]
126	DIFLIQ	Pr	Cl/CN	CSAPR-9	dmf	030	170.7	EC	[46]
127	XIKNUD	Yb	Cl/CN	CSAPR-9	dmf	030	167.0	EC	[48]

(^a) The geometry was determined with the program SHAPE [29,30,31,32,33,34,35,36]. CSAPR-9 = capped square antiprism; (^b) dmf = dimethylformamide, dmso = dimethyl sulfoxide, (^c) largest Ln-Ln-Ln angle in the hexagon; (^d) packing: EC = eclipsed, AL = alternated; (^e) Eu (98%)/Dy (2%).

2.3.4. Other 2D (Square) Lattices

As mentioned above, besides the 3,6-gon topology, although less common, there are also some 2D lattices with (3,4)-, (4,4)- and even mixed (3,4)+(3,8)-topologies (Table 6). The only reported example with the (3,4) topology is also the only known example with a coordination number of ten: [La₂(C₆O₄Cl₂)₃(H₂O)₆]·≈7H₂O (128) [16]. Although this compound has the general formula [Ln₂(anilato)₃(L)_n]·mG, in fact, the structure is very original since the La(III) ions are coordinated to three bidentate chloranilato ligands, two terminal water molecules and two bridging water molecules connecting two La(III) ions (Figure 16a). The coordination geometry of the La(III) ions is a sphenocorona (JSPC-10) [36] and the structure is formed by large squares containing four La(III) centers connected by bis-bidentate anilato ligands (as in other 4,4-lattices) and small rectangles with two anilato bridges and two double aquo-bridges (Figure 16d).

Although there are already twenty reported Ln-anilato compounds with the 4,4 topology (Table 6), the first compound with this topology, (H₃O)[Dy(C₆O₄(CN)Cl)₂(H₂O)]·4H₂O (129), was not reported until 2018 [46]. In this compound, the Dy(III) ions show a capped square antiprism (CSAPR-9) geometry with a water molecule in the capped position and four chlorocyananilato ligands occupying the closest positions of both square faces (Figure 16b). Accordingly, the four anilato ligands extend along four orthogonal directions, giving rise to a chessboard-like square lattice (Figure 4e) although it is not planar given the pushing effect of the water molecule (Figure 16e). The same structure has also been recently reported with the same ligand, but with NEt₂H₂⁺ instead of H₃O⁺ as cation, in (NEt₂H₂)[Dy(C₆O₄(CN)Cl)₂]·2dmf·2.5H₂O (130) [38]. In contrast with all the 3,6 lattices of the type [Ln₂(anilato)₃(L)_n], which are neutral, the 4,4 lattices are anionic since they are formed by two dianionic anilato ligands and one Ln(III) ion: [Ln(anilato)₂]⁻. The presence of cations in the structure represents an additional factor that may play a role in determining the final structure as we will see below. Although in compounds 129 and 130, the cations are H₃O⁺ and NEt₂H₂⁺, respectively, Robson et al. [57] have recently reported a large series with NEt₄⁺ cations and chloranilato formulated as: (NEt₄)[Ln(C₆O₄Cl₂)₂]·nG with Ln/n/G = Y/1.43/CS₂ (131), Y/0/- (132), Y/1.87/I₂ (133), Y/0.91/Br₂ (134), Dy/1.5/C₂H₆O (135), Gd/1/C₂H₆O (136), Yb/1/C₂H₆O (137), Er/1/C₂H₆O (138), Y/1/C₂H₆O (139), Tb/1.5/C₂H₆O (140), Lu/1.5/C₂H₆O (141) and Ho/1.5/C₂H₆O (142). This series was later enlarged by Harris et al. [58] with the Nd/0/- (143), Eu/0/- (144) and Sm/0/- (145) members and also with the Ce, La and Nd derivatives (see below) (Table 6). In this series, the coordination geometry is square antiprism (SAPR-8) with the Ln(III) ion coordinated by four bidentate anilato ligands that also occupy the closest positions of both square faces and extend along four orthogonal directions (Figure 16c) giving rise to a planar square lattice (Figure 16f) since now there is no additional water molecule. The role of the lanthanoid size is again evidenced in this series. Thus, for large lanthanoids such as La, Ce and Nd, there is room for an extra water molecule coordinated to the Ln(III) ions resulting in the series (NEt₄)[Ln(C₆O₄Cl₂)₂(H₂O)] with Ln = Ce (146), La (147) and Nd (148) [58]. In this series, the coordination geometry is capped square antiprism (CSAPR-9), as observed in compounds 129 and 130, with the water molecule located on the capped position (Figure 16b). An additional interesting aspect of this series is the single-crystal to single-crystal transformation observed in the Nd(III) derivative upon removal of the coordinated water molecule [58].

Table 6. Reported Ln-anilato complexes with 2D-(4,4), 2D-(3,4) and 2D-(3,4)+(3,8) structures.

#	CCDC	Structure	Ln	X	Geometry a	A+	L b	Disposition	α (°) c	Pk d	Reference
128	MIZYAV	3,4	La	Cl	JSPC-10	–	H2O	–	121.3	EC	[16]
129	DIFMAJ	4,4	Dy	Cl/CN	CSAPR-9	H3O+	H2O	100	89.2	EC	[46]
130	XOYVAL	4,4	Dy	Cl/CN	CSAPR-9	NEt2H2+	H2O	100	94.1	EC	[38]
131	QOFBAR	4,4	Y	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
132	QOFBOF	4,4	Y	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
133	QOFBUL	4,4	Y	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
134	QOFCAS	4,4	Y	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
135	QOFCEW	4,4	Dy	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
136	QOFNAD	4,4	Gd	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
137	QOFNEH	4,4	Yb	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
138	QOFNOR	4,4	Er	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
139	QOFNUX	4,4	Y	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
140	QOFPAF	4,4	Tb	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
141	QOFPEJ	4,4	Lu	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
142	QOFPIN	4,4	Ho	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
143	WOXTIP	4,4	Nd	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[58]
144	WOXTOV	4,4	Eu	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[58]
145	WOXTUB	4,4	Sm	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[58]
146	WOXVEN	4,4	Ce	Cl	CSAPR-9	NEt4+	H2O	100	90.0	EC	[58]
147	WOXVIR	4,4	La	Cl	CSAPR-9	NEt4+	H2O	100	90.0	EC	[58]
148	WOXVOX	4,4	Nd	Cl	CSAPR-9	NEt4+	H2O	100	90.0	EC	[58]
149	POMVIZ	(3,4) (3,8)	Er	Cl/CN	CSAPR-9		dmso	030	175.0 90.0	AL	[37]
150	XOYVEP	(3,4) (3,8)	Dy	Cl/CN	CSAPR-9		dmso	030	171.8 90.0	AL	[38]

(^a) The geometry was determined with the program SHAPE [29,30,31,32,33,34,35,36]. JSPC-10 = sphenocorona, CSAPR-9 = capped square antiprism, SAPR-8 = square antiprism; (^b) dmso = dimthylsulfoxide; (^c) largest Ln-Ln-Ln angle in the square; (^d) packing: EC = eclipsed, AL = alternated.

Table 6. Reported Ln-anilato complexes with 2D-(4,4), 2D-(3,4) and 2D-(3,4)+(3,8) structures.

#	CCDC	Structure	Ln	X	Geometry a	A+	L b	Disposition	α (°) c	Pk d	Reference
128	MIZYAV	3,4	La	Cl	JSPC-10	–	H2O	–	121.3	EC	[16]
129	DIFMAJ	4,4	Dy	Cl/CN	CSAPR-9	H3O+	H2O	100	89.2	EC	[46]
130	XOYVAL	4,4	Dy	Cl/CN	CSAPR-9	NEt2H2+	H2O	100	94.1	EC	[38]
131	QOFBAR	4,4	Y	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
132	QOFBOF	4,4	Y	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
133	QOFBUL	4,4	Y	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
134	QOFCAS	4,4	Y	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
135	QOFCEW	4,4	Dy	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
136	QOFNAD	4,4	Gd	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
137	QOFNEH	4,4	Yb	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
138	QOFNOR	4,4	Er	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
139	QOFNUX	4,4	Y	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
140	QOFPAF	4,4	Tb	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
141	QOFPEJ	4,4	Lu	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
142	QOFPIN	4,4	Ho	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[57]
143	WOXTIP	4,4	Nd	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[58]
144	WOXTOV	4,4	Eu	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[58]
145	WOXTUB	4,4	Sm	Cl	SAPR-8	NEt4+	–	–	90.0	EC	[58]
146	WOXVEN	4,4	Ce	Cl	CSAPR-9	NEt4+	H2O	100	90.0	EC	[58]
147	WOXVIR	4,4	La	Cl	CSAPR-9	NEt4+	H2O	100	90.0	EC	[58]
148	WOXVOX	4,4	Nd	Cl	CSAPR-9	NEt4+	H2O	100	90.0	EC	[58]
149	POMVIZ	(3,4) (3,8)	Er	Cl/CN	CSAPR-9		dmso	030	175.0 90.0	AL	[37]
150	XOYVEP	(3,4) (3,8)	Dy	Cl/CN	CSAPR-9		dmso	030	171.8 90.0	AL	[38]

(^a) The geometry was determined with the program SHAPE [29,30,31,32,33,34,35,36]. JSPC-10 = sphenocorona, CSAPR-9 = capped square antiprism, SAPR-8 = square antiprism; (^b) dmso = dimthylsulfoxide; (^c) largest Ln-Ln-Ln angle in the square; (^d) packing: EC = eclipsed, AL = alternated.

Finally, there are two original 2D structures with (3,4)-(3,8) lattices (Figure 4f and Figure 17a), formulated as [Ln₂(C₆O₄(CN)Cl)₃(dmso)₆]·nH₂O, with Ln/n = Er/0 (149) [37] and Dy/7 (150) [38]. In these (3,4)+(3,8) lattices, each Ln is connected to three other Ln through anilato bridges that extend in three orthogonal directions with a T-shape, generating eight-membered rings with four face-on (FO) and four edge-on (EO) anilato ligands together with four-membered rings with four EO anilato ligands (Figure 17a) [37,38]. The coordination geometry around the Ln(III) ions is also a CSAPR-9 with the solvent molecules occupying three vertices of the capped square face (030) and the anilato ligands with 110, 002 and 002 dispositions (Table 6 and Figure 17b).

2.4. Three Dimensional (3D) Lattices

As can be seen in Table 7, there are only seven reported 3D Ln-anilato compounds, all with chloranilato and six of them reported in 2019. Except compounds 156 and 157, they all show the well-known adamantane lattice (Figure 18a), although with large distortions. Most of the reported 3D lattices have been reported in a recent interesting study by Hua and Bondaruk [54] regarding the role of the geometry and size of the counter-cations on these anionic 3D lattices. Interestingly, the 3D-diamond lattice has the same basic formula as the 2D 4,4-lattices: [Ln(anilato)₂]⁻ and, therefore, it also needs a charge-balancing cation. The study of Hua and Bondaruk shows that the cation plays a key role in determining the dimensionality and the final topology since the cations establish, besides the electrostatic interactions with the anionic lattice, many different interactions such as H-bonds, π-π, Cl-π, halogen-H and CH-π interactions [54].

The first known 3D structure in the Ln-anilato family: (H₃O)[Y(C₆O₄Cl₂)₂]·8MeOH (151), was also reported by Robson, Abrahams et al. in their seminal work in 2002 [16], although a preliminary report had been published in 2000 [59]. This compound shows the typical adamantane structure although with distortions in the tetrahedral environment, that appears elongated along its C₂ axis. The coordination geometry around the Y atom is distorted TDD-8 (Figure 18b). In this compound, the presence of H₃O⁺ as counterion is proposed based on the lack of other cations and on charge-balance arguments [16].

Compound (NMe₂H2)[Tb2(C₆O₄Cl₂)3(dmf)2(H2O)2(HCOO)] (152) presents three long chloranilato bridges and a short formate one, resulting in a very distorted adamantane structure (Figure 18c) [60]. The Tb(III) ions in compound 152 are coordinated by three chloranilato ligands, one formate, one dmf and one water molecule in a CSAPR-9 coordination geometry (Figure 18d). The formate ion and the dmf molecule occupy two cis positions in the capped square face (010) and the water molecule occupies one vertex of the other square face (001), whereas the chloranilato ligands show 110, 011 and 002 dispositions (Figure 18d).

Table 7. Reported Ln-anilato complexes with 3D lattices.

#	CCDC	Structure	Ln	X	Geometry a	A+	L b	Disposition	Reference
151	MOBBIO	3D-diam	Y	Cl	TDD-8	H3O+	–	–	[16]
152	EFOXUV	3D-diam	Tb	Cl	CSAPR-9	NMe2H2+	H2O/dmf/HCOO-	001/010/010	[60]
153	JOGHEV	3D-diam	Er	Cl	SAPR-8	DPMP+	–	–	[54]
154	JOGHIZ	3D-diam	Ce	Cl	CSAPR-9	DPMP+	H2O	010	[54]
155	JOGHOF	3D-diam	Ce	Cl	TCTPR-9	PPh4+	H2O	010	[54]
156	JOGHUL	3D-noq	Ce1 Ce2 Ce3	Cl	CSAPR-9 CSAPR-9 TCTPR-9/MUFF	PPh3Me+	H2O H2O H2O	010 001 100	[54]
157	JOGJEX	3D-4,4-c	Er1/Er2	Cl	CSAPR-9/TDD-8	PPh3Me+	H2O/-	010/-	[54]

(^a) The geometry was determined with the program SHAPE [29,30,31,32,33,34,35,36]. TDD-8 = triangular dodecahedron, CSAPR-9 = capped square antiprism, SAPR-8 = square antiprism, TCTPR-9 = tri-capped trigonal prism; MUFF = muffin (^b) dmf = dimethylformamide.

Table 7. Reported Ln-anilato complexes with 3D lattices.

#	CCDC	Structure	Ln	X	Geometry a	A+	L b	Disposition	Reference
151	MOBBIO	3D-diam	Y	Cl	TDD-8	H3O+	–	–	[16]
152	EFOXUV	3D-diam	Tb	Cl	CSAPR-9	NMe2H2+	H2O/dmf/HCOO-	001/010/010	[60]
153	JOGHEV	3D-diam	Er	Cl	SAPR-8	DPMP+	–	–	[54]
154	JOGHIZ	3D-diam	Ce	Cl	CSAPR-9	DPMP+	H2O	010	[54]
155	JOGHOF	3D-diam	Ce	Cl	TCTPR-9	PPh4+	H2O	010	[54]
156	JOGHUL	3D-noq	Ce1 Ce2 Ce3	Cl	CSAPR-9 CSAPR-9 TCTPR-9/MUFF	PPh3Me+	H2O H2O H2O	010 001 100	[54]
157	JOGJEX	3D-4,4-c	Er1/Er2	Cl	CSAPR-9/TDD-8	PPh3Me+	H2O/-	010/-	[54]

(^a) The geometry was determined with the program SHAPE [29,30,31,32,33,34,35,36]. TDD-8 = triangular dodecahedron, CSAPR-9 = capped square antiprism, SAPR-8 = square antiprism, TCTPR-9 = tri-capped trigonal prism; MUFF = muffin (^b) dmf = dimethylformamide.

The diamond net is also observed in the closely related compounds: (DPMP)[Er(C₆O₄Cl₂)₂] (153), (DPMP)[Ce(C₆O₄Cl₂)₂(H₂O)]·H₂O·C₃H₆O (154) and (PPh₄)[Ce(C₆O₄Cl₂)₂(H₂O)] (155) (DPMP = 1-(diphenylmethyl)-pyridinium) [54]. These three compounds show the effect of the cation and of the size of the Ln(III) ion in the coordination geometry. Thus, the small Er(III) ion in compound 153 can only accommodate four chloranilato ligands in a square antiprism geometry (Figure 19a), giving rise to a quite regular diamond net (Figure 19b). In contrast, the larger Ce(III) ion in compounds 154 and 155 allows the coordination of an additional water molecule, resulting in a distorted CSAPR-9 in 154 (with a 010 disposition for the water molecule, Figure 19c) and in a distorted TCTPR-9 in 155 (with a 100 disposition for the water molecule, Figure 19d). Interestingly, the coordination of the additional water molecule does not change the diamond net topology but increases the distortions of the lattice. Another interesting point of this series is the change in the coordination geometry (CSAPR-9 in 154 vs. TCTPR-9 in 155). This change can be attributed to the different symmetry and shape of the cations used to prepare both compounds: DPMP⁺ in 154 and PPh₄⁺ in 155. A similar effect of the symmetry and shape of closely related cations of the type NR₄⁺ and PR₄⁺ was observed in a series of tris-anilato-metalate complexes with transition metals [9].

A remarkable fact is that compounds (NEt₄)[Y(C₆O₄Cl₂)₃] (132) and (H₃O)[Y(C₆O₄Cl₂)₂]·8MeOH (151) show the same coordination environment around the Y(III) ions (four bidentante chloranilato ligands) but the geometries are different: SAPR-8 in 132 (Figure 16c) vs. TDD-8 in 151 (Figure 18b). This simple difference in the coordination geometry gives rise to different spatial orientations of the anilato ligands (square in 132 and tetrahedral in 151) that originate two very different structures (a 2D 4,4-square lattice in 132 vs. a 3D diamond net in 151). Since the ligand and the Ln(III) ion are the same in both compounds, these differences might be only attributed to the different counter-cation in each lattice: NEt₄⁺ in 131 vs. H₃O⁺ in 151.

Besides the five mentioned examples of diamond 3D lattices, there are two more examples of Ln-anilato 3D lattices: compound (PPh₃Me)[Ce(C₆O₄Cl₂)₂(H₂O)] (156) shows a very original 3D structure with three unique Ce(III) ions nonacoordinated by four bidentate chloranilato ligands and a water molecule [54]. Ce1 and Ce2 show both a CSAPR-9 geometry although the water molecule is located on the capped square face in Ce1 (010, Figure 20a) or in the basal square face in Ce2 (001, Figure 20b). In contrast, Ce3 presents a geometry in between TCTPR-9 and MFF (Muffin) [35] with the water molecule coordinated on one of the triangular faces (100, Figure 20c). The structure can be described as a 3D-noq anionic lattice formed by three-, four- and five-membered rings with PPh₃Me⁺ cations inserted in the larger cavities (Figure 20d).

Finally, compound (PPh₃Me)[Er(C₆O₄Cl₂)₂]·1/2H₂O (157) shows a unique 3D 4,4′-c structure with four- and five-membered rings (Figure 21a) and net point symbol {4.5².7³}{4.5³.7²} with PPh₃Me⁺ cations located in the five-membered rings [54]. In this compound, there are two unique Er(III) ions with different coordination geometries. Er1 ion is surrounded by four chloranilato ligands and a water molecule in a CSAPR-9 geometry with the water molecule located on the capped square face (010, Figure 21b), whereas Er2 is surrounded by four chloranilato ligands in a TDD-8 geometry without any additional coligand (Figure 21c).

2.5. Anilato-Type Ligands

A second way to classify the above Ln-anilato compounds is based on the anilato-type ligand. With this criterion, we can see that there are nineteen compounds with lanthanoids and the ligand dhbq²⁻ (

Table 8. Structurally characterized Ln compounds with dhbq²⁻.

#	CCDC	Structure	Ln	X	L a	Reference
2	DEHQUF	Dimer	Dy	H	thf/Cl-	[21]
3	DEHRAM	Dimer	Y	H	thf/Cl-	[21]
10	DEKVEX	Dimer	Y	H	Tp-	[20]
35	KUYKIZ	2D-hex	Ho	H	H2O	[43]
36	MIZXAU	2D-hex	La	H	H2O	[16]
37	MIZXEY	2D-hex	Gd	H	H2O	[16]
38	MIZXIC	2D-hex	Yb	H	H2O	[16]
39	MIZXOI	2D-hex	Lu	H	H2O	[16]
40	MIZXUO	2D-hex	Y	H	H2O	[16]
41	PIVKAJ	2D-hex	Er	H	H2O	[44]
42	ZOTTAD	2D-hex	Ce	H	H2O	[15]
43	1944109	2D-hex	Pr	H	H2O	[45]
44	1944110	2D-hex	Nd	H	H2O	[45]
45	1944111	2D-hex	Sm	H	H2O	[45]
46	1944112	2D-hex	Eu	H	H2O	[45]
47	1944113	2D-hex	Tb	H	H2O	[45]
48	1944114	2D-hex	Dy	H	H2O	[45]
49	1944117	2D-hex	Tm	H	H2O	[45]
95	LEBGEG	2D-dist.hex	Gd	H	thf/Cl-	[53]

(^a) thf = tetrahydrofurane, Tp^- = HB(pz)₃^- = hydrotris(pyrazolyl)borate.

). Among these nineteen compounds, three are dimers, one shows a distorted hexagonal 2D lattice and the remaining fifteen compounds present a regular hexagonal 2D lattice.

By far, the most used anilato ligand with lanthanoids is chloranilato (X = Cl), with a total of 63 structurally characterized compounds (

Table 9. Structurally characterized Ln compounds with chloranilato.

#	CCDC	Structure	Ln	X	L a	A+b	Reference
1	PIQFUT	Monomer	Dy	Cl	Tp-	–	[19]
4	DEKTOF	Dimer	Dy	Cl	Tp-	–	[20]
5	DEKTOF01	Dimer	Dy	Cl	Tp-	–	[22]
6	DEKTOF02	Dimer	Dy	Cl	Tp-	–	[19]
7	DEKTUL	Dimer	Y	Cl	Tp-	–	[20]
8	DEKTUL01	Dimer	Y	Cl	Tp-	–	[22]
9	DEKVAT	Dimer	Y	Cl	Tp-	–	[20]
22	KOZBEJ	Dimer	Er	Cl	Tp-	–	[24]
23	KOZBIN	Dimer	Ho	Cl	Tp-	–	[24]
24	LEPNIG	Dimer	Tb	Cl	Tp-	–	[22]
25	LEPNIG01	Dimer	Tb	Cl	Tp-	–	[24]
26	LEPNOM	Dimer	Gd	Cl	Tp-	–	[22]
27	LEPNOM01	Dimer	Gd	Cl	Tp-	–	[19]
28	OBIBEH	Dimer	Yb	Cl	Tp-	–	[25]
29	OBIBEH01	Dimer	Yb	Cl	Tp-	–	[24]
33	MIZZUQ	1D + mon	Lu	Cl	H2O	–	[16]
34	NIGNID	1D-ladder	Er	Cl	hmpa	–	[28]
56	NIGNUP	2D-hex	Er	Cl	fma	–	[28]
57	GEQBAH	2D-dist.hex	Gd	Cl	H2O	–	[49]
58	MIZYID	2D-dist.hex	Pr	Cl	H2O	–	[16]
59	MIZYOJ	2D-dist.hex	Nd	Cl	H2O	–	[16]
60	MIZYUP	2D-dist.hex	Tb	Cl	H2O	–	[16]
61	MIZZAW	2D-dist.hex	Ce	Cl	H2O	–	[16]
62	MIZZAW01	2D-dist.hex	Ce	Cl	H2O	–	[16]
63	MIZZEA	2D-dist.hex	Y	Cl	H2O	–	[16]
64	MIZZIE	2D-dist.hex	Gd	Cl	H2O	–	[16]
65	MIZZOK	2D-dist.hex	Eu	Cl	H2O	–	[16]
66	NIGNEZ	2D-dist.hex	Er	Cl	H2O	–	[28]
67	1944118	2D-dist.hex	La	Cl	H2O	–	[45]
68	1944120	2D-dist.hex	Sm	Cl	H2O	–	[45]
69	1944123	2D-dist.hex	Dy	Cl	H2O	–	[45]
70	1944124	2D-dist.hex	Ho	Cl	H2O	–	[45]
90	NIGQIG	2D-dist.hex	Er	Cl	dmso	–	[28]
91	NIGNOJ	2D-dist.hex	Er	Cl	dma	–	[28]
96	CAZZAE	2D-brickwall	Pr	Cl	EtOH	–	[13]
97	GASMUI	2D-brickwall	Y	Cl	H2O	–	[14]
98	JOGJAT	2D-brickwall	Er	Cl	H2O	–	[54]
99	1944126	2D-brickwall	Tm	Cl	H2O	–	[45]
100	1944127	2D-brickwall	Yb	Cl	H2O	–	[45]
110	GEPZUY	2D-brickwall	Eu	Cl	bipym/H2O	–	[49]
113	GEQBEL	2D-herringbone	Gd	Cl	H2O	–	[49]
114	JOGHAR	2D-herringbone	Ce	Cl	H2O	–	[54]
115	NIGPAX	2D-herringbone	Er	Cl	dmf	–	[28]
128	MIZYAV	2D-3,4	La	Cl	H2O	–	[16]
131	QOFBAR	2D-4,4	Y	Cl	–	NEt4+	[57]
132	QOFBOF	2D-4,4	Y	Cl	–	NEt4+	[57]
133	QOFBUL	2D-4,4	Y	Cl	–	NEt4+	[57]
134	QOFCAS	2D-4,4	Y	Cl	–	NEt4+	[57]
135	QOFCEW	2D-4,4	Dy	Cl	–	NEt4+	[57]
136	QOFNAD	2D-4,4	Gd	Cl	–	NEt4+	[57]
137	QOFNEH	2D-4,4	Yb	Cl	–	NEt4+	[57]
138	QOFNOR	2D-4,4	Er	Cl	–	NEt4+	[57]
139	QOFNUX	2D-4,4	Y	Cl	–	NEt4+	[57]
140	QOFPAF	2D-4,4	Tb	Cl	–	NEt4+	[57]
141	QOFPEJ	2D-4,4	Lu	Cl	–	NEt4+	[57]
142	QOFPIN	2D-4,4	Ho	Cl	–	NEt4+	[57]
143	WOXTIP	2D-4,4	Nd	Cl	–	NEt4+	[58]
144	WOXTOV	2D-4,4	Eu	Cl	–	NEt4+	[58]
145	WOXTUB	2D-4,4	Sm	Cl	–	NEt4+	[58]
146	WOXVEN	2D-4,4	Ce	Cl	H2O	NEt4+	[58]
147	WOXVIR	2D-4,4	La	Cl	H2O	NEt4+	[58]
148	WOXVOX	2D-4,4	Nd	Cl	H2O	NEt4+	[58]
151	MOBBIO	3D-diam	Y	Cl	–	H3O+	[16]
152	EFOXUV	3D-diam	Tb	Cl	H2O/dmf/HCOO-	NMe2H2+	[60]
153	JOGHEV	3D-diam	Er	Cl	–	DPMP+	[54]
154	JOGHIZ	3D-diam	Ce	Cl	H2O	DPMP+	[54]
155	JOGHOF	3D-diam	Ce	Cl	H2O	PPh4+	[54]
156	JOGHUL	3D-noq	Ce	Cl	H2O	PPh3Me+	[54]
157	JOGJEX	3D-4,4-c	Er1	Cl	H2O	PPh3Me+	[54]

(^a) Tp^- = HB(pz)₃^- = hydrotris(pyrazolyl)borate, hmpa = hexamethylphosphoramide, fma = formamide, dmso = dimthylsulfoxide, dma = dimethylacetamide, bipym = 2,2′-bipyrimidine, dmf = dimethylformamide; (^b) DPMP⁺ = 1-(diphenylmethyl)-pyridinium.

) with all the dimensionalities (0D, 1D, 2D and 3D). Among these 63 compounds, there is one monomer, one compound formed by a monomer and a chain, eight dimers, one ladder chain, one regular hexagonal 2D lattice, sixteen distorted hexagonal layers, six rectangular brick-wall 2D lattices, three rectangular herringbone layers, one 2D-3,4 lattice, eighteen 2D-4,4 square layers, five adamantane 3D structures, one 3D-noq and one 3D-4,4-c lattice.

With the ligand bromanilato (X = Br), there are 31 compounds (

Table 10. Structurally characterized Ln compounds with bromanilato.

#	CCDC	Structure	Ln	X	L a	Reference
18	JOQSEQ	Dimer	Dy	Br	Tp-	[23]
21	JOQSUG	Dimer	Y	Br	Tp-	[23]
71	XAWZUT	2D-dist.hex	Er	Br	H2O	[50]
72	1565271	2D-dist.hex	La	Br	H2O	[45]
73	1565272	2D-dist.hex	Ce	Br	H2O	[45]
74	1565273	2D-dist.hex	Pr	Br	H2O	[45]
75	1565274	2D-dist.hex	Nd	Br	H2O	[45]
76	1565275	2D-dist.hex	Sm	Br	H2O	[45]
77	1565276	2D-dist.hex	Eu	Br	H2O	[45]
78	1565277	2D-dist.hex	Gd	Br	H2O	[45]
79	1565278	2D-dist.hex	Tb	Br	H2O	[45]
80	1565279	2D-dist.hex	Dy	Br	H2O	[45]
81	1565280	2D-dist.hex	Ho	Br	H2O	[45]
82	NIDFOY	2D-dist.hex	Tb	Br	dmso	[51]
83	NIDFUE	2D-dist.hex	Dy	Br	dmso	[51]
84	NIDGAL	2D-dist.hex	Ho	Br	dmso	[51]
85	XAXBAC	2D-dist.hex	Er	Br	dmso	[50]
86	NIDGEP	2D-dist.hex	Yb	Br	dmso	[51]
101	GASMOC	2D-brickwall	Y	Br	H2O	[14]
102	1565282	2D-brickwall	Tm	Br	H2O	[45]
103	LUTRIE	2D-brickwall	Yb	Br	H2O	[55]
116	NIDLIY	2D-herringbone	La	Br	dmso	[51]
117	NIDLOE	2D-herringbone	Ce	Br	dmso	[51]
118	NIDLUK	2D-herringbone	Pr	Br	dmso	[51]
119	NIDMAR	2D-herringbone	Nd	Br	dmso	[51]
120	NIDMEV	2D-herringbone	Sm	Br	dmso	[51]
121	NIDFEO	2D-herringbone	Eu	Br	dmso	[51]
122	NIDFIS	2D-herringbone	Gd	Br	dmso	[51]
123	NOQBON	2D-herringbone	Eu/Dy	Br	dmso	[27]
124	XAXBEG	2D-herringbone	Er	Br	dmf	[50]
125	LUTROK	2D-herringbone	Dy	Br	dmf	[55]

(^a) dmso = dimthylsulfoxide, dmf = dimethylformamide.

): two dimers, sixteen distorted hexagonal layers, three rectangular brick-wall layers and ten rectangular herringbone ones.

With the asymmetric ligand chlorocyananilato (X = Cl/CN), there is a total of 25 reported compounds (

Table 11. Structurally characterized Ln compounds with chlorocyananilato.

#	CCDC	Structure	Ln	X	L a	A+	Reference
30	NOQBUT	Dimer-zz	Eu	Cl/CN	H2O	–	[27]
31	NOQGEI	Dimer-zz	Eu/Dy b	Cl/CN	H2O	–	[27]
50	DIFLEM	2D-hex	Ce	Cl/CN	dmf	–	[46]
51	WOTWIO	2D-hex	Dy	Cl/CN	dmf	–	[47]
52	WOTWOU	2D-hex	Ho	Cl/CN	dmf	–	[47]
53	XIKNOX	2D-hex	Nd	Cl/CN	dmf	–	[48]
54	XIKPAL	2D-hex	Er	Cl/CN	dmf	–	[48]
55	XOYTEN	2D-hex	Dy	Cl/CN	dmf	–	[38]
87	DIFLUC	2D-dist.hex	Yb	Cl/CN	dmso	–	[46]
88	POMTUJ	2D-dist.hex	Yb	Cl/CN	dmso	–	[37]
89	POMVAR	2D-dist.hex	Yb/Er	Cl/CN	dmso	–	[37]
104	DIFLOW	2D-brickwall	Pr	Cl/CN	dmso	–	[46]
105	NOQGAE	2D-brickwall	Eu/Dy	Cl/CN	dmso	–	[27]
106	WOTWUA	2D-brickwall	Ce	Cl/CN	dmso	–	[47]
107	WOTXAH	2D-brickwall	Nd	Cl/CN	dmso	–	[47]
108	XOYTUD	2D-brickwall	Dy	Cl/CN	dmso	–	[38]
109	WOTWEK	2D-brickwall	Nd	Cl/CN	dmf	–	[47]
111	QOVJUJ	2D-brickwall	Yb1	Cl/CN	dmso/dobdc2-	–	[56]
112	QOVJOD	2D-brickwall	Yb	Cl/CN	dmso/F4bdc2-	–	[56]
126	DIFLIQ	2D-herringbone	Pr	Cl/CN	dmf	–	[46]
127	XIKNUD	2D-herringbone	Yb	Cl/CN	dmf	–	[48]
129	DIFMAJ	2D-4,4	Dy	Cl/CN	H2O	H3O+	[46]
130	XOYVAL	2D-4,4	Dy	Cl/CN	H2O	NEt2H2+	[38]
149	POMVIZ	2D-(3,4)+(3,8)	Er	Cl/CN	dmso	–	[37]
150	XOYVEP	2D-(3,4)+(3,8)	Dy	Cl/CN	dmso	–	[38]

(^a) dmf = dimethylformamide, dmso = dimthylsulfoxide, H₂dobdc = 2,5-dihydroxybenzene-1,4-dicarboxylic acid, H₂F₄bdc = 2,3,5,6-tetrafluorobenzene-1,4-dicarboxylic acid; (^b) Eu (98%)/Dy (2%).

). Among these 25 compounds, two are zigzag dimers, six are 2D regular hexagonal layers, three are distorted hexagonal lattices, eight are rectangular brick-wall lattices, two are rectangular herringbone lattices, two are square 4,4 layers and the remaining two are (3,4)+(3,8) layers.

Finally, there are a few reported compounds with lanthanoids and other anilato ligands (

Table 12. Structurally characterized Ln compounds with other anilato-type ligands.

#	CCDC	Structure	Ln	X	L a	Reference
11	DEKVIB	Dimer	Y	CH3	Tp-	[20]
12	DEKVOH	Dimer	Y	CH3	Tp-	[20]
32	DEKVUN	Tetramer	Y	CH3	Tp-/(MeO)4B/MeOH	[20]
13	EDEZAR	Dimer	Gd	NO2	H2O	[26]
14	EDEZEV	Dimer	Tb	NO2	H2O	[26]
15	EDEZIZ	Dimer	Dy	NO2	H2O	[26]
16	EDEZOF	Dimer	Ho	NO2	H2O	[26]
17	EDEZUL	Dimer	Sm	NO2	H2O	[26]
19	JOQSIU	Dimer	Dy	F	Tp-	[23]
20	JOQSOA	Dimer	Y	F	Tp-	[23]
92	KUVBIP	2D-dist.hex	La	t-Bu	dma	[52]
93	KUVBOV	2D-dist.hex	Pr	t-Bu	dma	[52]
94	KUVBUB	2D-dist.hex	Nd	t-Bu	dma	[52]

(^a) Tp^- = HB(pz)₃^- = hydrotris(pyrazolyl)borate, dma = dimethylacetamide.

) such as: methylanilato (X = CH₃), with three reported examples [20], nitranilato (X = NO₂), with five reported compounds [26], fluoranilato (X = F), with two reported compounds [23] and tert-butylanilato (X = t-Bu), with three very recently reported examples [52].

2.6. Lanthanoid Metal Ions

If we classify all the Ln-anilato compounds based on the lanthanoid metal ion, we can see that there are eighteen compounds with Y(III) (

Table 13. Structurally characterized Y(III) compounds with anilato ligands.

#	CCDC	Structure	Ln	X	L	A+	Reference
3	DEHRAM	Dimer	Y	H	thf/Cl-	–	[21]
7	DEKTUL	Dimer	Y	Cl	Tp-	–	[20]
8	DEKTUL01	Dimer	Y	Cl	Tp-	–	[22]
9	DEKVAT	Dimer	Y	Cl	Tp-	–	[20]
10	DEKVEX	Dimer	Y	H	Tp-	–	[20]
11	DEKVIB	Dimer	Y	CH3	Tp-	–	[20]
12	DEKVOH	Dimer	Y	CH3	Tp-	–	[20]
20	JOQSOA	Dimer	Y	F	Tp-	–	[23]
21	JOQSUG	Dimer	Y	Br	Tp-	–	[23]
32	DEKVUN	Tetramer	Y	CH3	Tp-/(MeO)4B/MeOH	–	[20]
40	MIZXUO	2D-hex	Y	H	H2O	–	[16]
63	MIZZEA	2D-dist.hex	Y	Cl	H2O	–	[16]
97	GASMUI	2D-brickwall	Y	Cl	H2O	–	[14]
101	GASMOC	2D-brickwall	Y	Br	H2O	–	[14]
132	QOFBOF	2D-4,4	Y	Cl	–	NEt4+	[57]
133	QOFBUL	2D-4,4	Y	Cl	–	NEt4+	[57]
134	QOFCAS	2D-4,4	Y	Cl	–	NEt4+	[57]
139	QOFNUX	2D-4,4	Y	Cl	–	NEt4+	[57]
151	MOBBIO	3D-diam	Y	Cl	–	H3O+	[16]

), seven with La(III) (

Table 14. Structurally characterized La(III) compounds with anilato ligands.

#	CCDC	Structure	Ln	X	L	A+	Reference
36	MIZXAU	2D-hex	La	H	H2O	–	[16]
67	1944118	2D-dist.hex	La	Cl	H2O	–	[45]
72	1565271	2D-dist.hex	La	Br	H2O	–	[45]
92	KUVBIP	2D-dist.hex	La	t-Bu	dma	–	[52]
116	NIDLIY	2D-herringbone	La	Br	dmso	–	[51]
128	MIZYAV	2D-3,4	La	Cl	H2O	–	[16]
147	WOXVIR	2D-4,4	La	Cl	H2O	NEt4+	[58]

), twelve with Ce(III) (

Table 15. Structurally characterized Ce(III) compounds with anilato ligands.

#	CCDC	Structure	Ln	X	L	A+	Reference
42	ZOTTAD	2D-hex	Ce	H	H2O	–	[15]
50	DIFLEM	2D-hex	Ce	Cl/CN	dmf	–	[46]
61	MIZZAW	2D-dist.hex	Ce	Cl	H2O	–	[16]
62	MIZZAW01	2D-dist.hex	Ce	Cl	H2O	–	[16]
73	1565272	2D-dist.hex	Ce	Br	H2O	–	[45]
106	WOTWUA	2D-brickwall	Ce	Cl/CN	dmso	–	[47]
114	JOGHAR	2D-herringbone	Ce	Cl	H2O	–	[54]
117	NIDLOE	2D-herringbone	Ce	Br	dmso	–	[51]
146	WOXVEN	2D-4,4	Ce	Cl	H2O	NEt4+	[58]
154	JOGHIZ	3D-diam	Ce	Cl	H2O	DPMP+	[54]
155	JOGHOF	3D-diam	Ce	Cl	H2O	PPh4+	[54]
156	JOGHUL	3D-noq	Ce	Cl	H2O	PPh3Me+	[54]

), eight with Pr(III) (

Table 16. Structurally characterized Pr(III) compounds with anilato ligands.

#	CCDC	Structure	Ln	X	L	Reference
43	1944109	2D-hex	Pr	H	H2O	[45]
58	MIZYID	2D-dist.hex	Pr	Cl	H2O	[16]
74	1565273	2D-dist.hex	Pr	Br	H2O	[45]
93	KUVBOV	2D-dist.hex	Pr	t-Bu	Dma	[52]
96	CAZZAE	2D-brickwall	Pr	Cl	EtOH	[13]
104	DIFLOW	2D-brickwall	Pr	Cl/CN	dmso	[46]
118	NIDLUK	2D-herringbone	Pr	Br	dmso	[51]
126	DIFLIQ	2D-herringbone	Pr	Cl/CN	Dmf	[46]

), ten with Nd(III) (

Table 17. Structurally characterized Nd(III) compounds with anilato ligands.

#	CCDC	Structure	Ln	X	L	A+	Reference
44	1944110	2D-hex	Nd	H	H2O	–	[45]
53	XIKNOX	2D-hex	Nd	Cl/CN	dmf	–	[48]
59	MIZYOJ	2D-dist.hex	Nd	Cl	H2O	–	[16]
75	1565274	2D-dist.hex	Nd	Br	H2O	–	[45]
94	KUVBUB	2D-dist.hex	Nd	t-Bu	dma	–	[52]
107	WOTXAH	2D-brickwall	Nd	Cl/CN	dmso	–	[47]
109	WOTWEK	2D-brickwall	Nd	Cl/CN	dmf	–	[47]
119	NIDMAR	2D-herringbone	Nd	Br	dmso	–	[51]
143	WOXTIP	2D-4,4	Nd	Cl	–	NEt4+	[58]
148	WOXVOX	2D-4,4	Nd	Cl	H2O	NEt4+	[58]

), six with Sm(III) (

Table 18. Structurally characterized Sm(III) compounds with anilato ligands.

#	CCDC	Structure	Ln	X	L	A+	Reference
17	EDEZUL	Dimer	Sm	NO2	H2O	–	[26]
45	1944111	2D-hex	Sm	H	H2O	–	[45]
68	1944120	2D-dist.hex	Sm	Cl	H2O	–	[45]
76	1565275	2D-dist.hex	Sm	Br	H2O	–	[45]
120	NIDMEV	2D-herringbone	Sm	Br	dmso	–	[51]
145	WOXTUB	2D-4,4	Sm	Cl	–	NEt4+	[58]

), ten with Eu(III) (including three Dy-doped compounds,

Table 19. Structurally characterized Eu(III) compounds with anilato ligands.

#	CCDC	Structure	Ln	X	L	A+	Reference
30	NOQBUT	Dimer-zz	Eu	Cl/CN	H2O	–	[27]
31	NOQGEI	Dimer-zz	Eu/Dy	Cl/CN	H2O	–	[27]
46	1944112	2D-hex	Eu	H	H2O	–	[45]
65	MIZZOK	2D-dist.hex	Eu	Cl	H2O	–	[16]
77	1565276	2D-dist.hex	Eu	Br	H2O	–	[45]
105	NOQGAE	2D-brickwall	Eu/Dy	Cl/CN	dmso	–	[27]
110	GEPZUY	2D-brickwall	Eu	Cl	bipym/H2O	–	[49]
121	NIDFEO	2D-herringbone	Eu	Br	dmso	–	[51]
123	NOQBON	2D-herringbone	Eu/Dy	Br	dmso	–	[27]
144	WOXTOV	2D-4,4	Eu	Cl	–	NEt4+	[58]

), ten with Gd(III) (

Table 20. Structurally characterized Gd(III) compounds with anilato ligands.

#	CCDC	Structure	Ln	X	L	A+	Reference
13	EDEZAR	Dimer	Gd	NO2	H2O	–	[26]
26	LEPNOM	Dimer	Gd	Cl	Tp-	–	[22]
27	LEPNOM01	Dimer	Gd	Cl	Tp-	–	[19]
37	MIZXEY	2D-hex	Gd	H	H2O	–	[16]
57	GEQBAH	2D-dist.hex	Gd	Cl	H2O	–	[49]
64	MIZZIE	2D-dist.hex	Gd	Cl	H2O	–	[16]
78	1565277	2D-dist.hex	Gd	Br	H2O	–	[45]
95	LEBGEG	2D-dist.hex	Gd	H	thf/Cl-	–	[53]
113	GEQBEL	2D-herringbone	Gd	Cl	H2O	–	[49]
122	NIDFIS	2D-herringbone	Gd	Br	dmso	–	[51]
136	QOFNAD	2D-4,4	Gd	Cl	–	NEt4+	[57]

), eight with Tb(III) (

Table 21. Structurally characterized Tb(III) compounds with anilato ligands.

#	CCDC	Structure	Ln	X	L	A+	Reference
14	EDEZEV	Dimer	Tb	NO2	H2O	–	[26]
24	LEPNIG	Dimer	Tb	Cl	Tp-	–	[22]
25	LEPNIG01	Dimer	Tb	Cl	Tp-	–	[24]
47	1944113	2D-hex	Tb	H	H2O	–	[45]
60	MIZYUP	2D-dist.hex	Tb	Cl	H2O	–	[16]
79	1565278	2D-dist.hex	Tb	Br	H2O	–	[45]
82	NIDFOY	2D-dist.hex	Tb	Br	dmso	–	[51]
140	QOFPAF	2D-4,4	Tb	Cl	–	NEt4+	[57]
152	EFOXUV	3D-diam	Tb	Cl	H2O/dmf/HCOO-	NMe2H2+	[60]

), eighteen with Dy(III) (

Table 22. Structurally characterized Dy(III) compounds with anilato ligands.

#	CCDC	Structure	Ln	X	L	A+	Reference
1	PIQFUT	Monomer	Dy	Cl	Tp-	–	[19]
2	DEHQUF	Dimer	Dy	H	thf/Cl-	–	[21]
4	DEKTOF	Dimer	Dy	Cl	Tp-	–	[20]
5	DEKTOF01	Dimer	Dy	Cl	Tp-	–	[22]
6	DEKTOF02	Dimer	Dy	Cl	Tp-	–	[19]
15	EDEZIZ	Dimer	Dy	NO2	H2O	–	[26]
18	JOQSEQ	Dimer	Dy	Br	Tp-	–	[23]
19	JOQSIU	Dimer	Dy	F	Tp-	–	[23]
48	1944114	2D-hex	Dy	H	H2O	–	[45]
51	WOTWIO	2D-hex	Dy	Cl/CN	dmf	–	[47]
55	XOYTEN	2D-hex	Dy	Cl/CN	dmf	–	[38]
69	1944123	2D-dist.hex	Dy	Cl	H2O	–	[45]
80	1565279	2D-dist.hex	Dy	Br	H2O	–	[45]
83	NIDFUE	2D-dist.hex	Dy	Br	dmso	–	[51]
108	XOYTUD	2D-brickwall	Dy	Cl/CN	dmso	–	[38]
125	LUTROK	2D-herringbone	Dy	Br	dmf	–	[55]
129	DIFMAJ	2D-4,4	Dy	Cl/CN	H2O	H3O+	[46]
130	XOYVAL	2D-4,4	Dy	Cl/CN	H2O	NEt2H2+	[38]
135	QOFCEW	2D-4,4	Dy	Cl	–	NEt4+	[57]
150	XOYVEP	2D-(3,4)+(3,8)	Dy	Cl/CN	dmso	–	[38]

), eight with Ho(III) (

Table 23. Structurally characterized Ho(III) compounds with anilato ligands.

#	CCDC	Structure	Ln	X	L	A+	Reference
16	EDEZOF	Dimer	Ho	NO2	H2O	–	[26]
23	KOZBIN	Dimer	Ho	Cl	Tp-	–	[24]
35	KUYKIZ	2D-hex	Ho	H	H2O	–	[43]
52	WOTWOU	2D-hex	Ho	Cl/CN	dmf	–	[47]
70	1944124	2D-dist.hex	Ho	Cl	H2O	–	[45]
81	1565280	2D-dist.hex	Ho	Br	H2O	–	[45]
84	NIDGAL	2D-dist.hex	Ho	Br	dmso	–	[51]
142	QOFPIN	2D-4,4	Ho	Cl	–	NEt4+	[57]

), eighteen with Er(III) (including one Er/Yb (1:1) compound,

Table 24. Structurally characterized Er(III) compounds with anilato ligands.

#	CCDC	Structure	Ln	X	L	A+	Reference
22	KOZBEJ	Dimer	Er	Cl	Tp-	–	[24]
34	NIGNID	1D-ladder	Er	Cl	hmpa	–	[28]
41	PIVKAJ	2D-hex	Er	H	H2O	–	[44]
54	XIKPAL	2D-hex	Er	Cl/CN	dmf	–	[48]
56	NIGNUP	2D-hex	Er	Cl	fma	–	[28]
66	NIGNEZ	2D-dist.hex	Er	Cl	H2O	–	[28]
71	XAWZUT	2D-dist.hex	Er	Br	H2O	–	[50]
85	XAXBAC	2D-dist.hex	Er	Br	dmso	–	[50]
89	POMVAR	2D-dist.hex	Yb/Er	Cl/CN	dmso	–	[37]
90	NIGQIG	2D-dist.hex	Er	Cl	dmso	–	[28]
91	NIGNOJ	2D-dist.hex	Er	Cl	dma	–	[28]
98	JOGJAT	2D-brickwall	Er	Cl	H2O	–	[53]
115	NIGPAX	2D-herringbone	Er	Cl	dmf	–	[28]
124	XAXBEG	2D-herringbone	Er	Br	dmf	–	[50]
138	QOFNOR	2D-4,4	Er	Cl	–	NEt4+	[57]
149	POMVIZ	2D-(3,4)+(3,8)	Er	Cl/CN	dmso	–	[37]
153	JOGHEV	3D-diam	Er	Cl	–	DPMP+	[54]
157	JOGJEX	3D-4,4-c	Er	Cl	H2O	PPh3Me+	[54]

), three with Tm(III) (

Table 25. Structurally characterized Tm(III) compounds with anilato ligands.

#	CCDC	Structure	Ln	X	L	Reference
49	1944117	2D-hex	Tm	H	H2O	[45]
99	1944126	2D-brickwall	Tm	Cl	H2O	[45]
102	1565282	2D-brickwall	Tm	Br	H2O	[45]

), twelve with Yb(III) (including one Er/Yb (1:1) compound,

Table 26. Structurally characterized Yb(III) compounds with anilato ligands.

#	CCDC	Structure	Ln	X	L	A+	Reference
28	OBIBEH	Dimer	Yb	Cl	Tp-	–	[25]
29	OBIBEH01	Dimer	Yb	Cl	Tp-	–	[24]
38	MIZXIC	2D-hex	Yb	H	H2O	–	[16]
86	NIDGEP	2D-dist.hex	Yb	Br	dmso	–	[51]
87	DIFLUC	2D-dist.hex	Yb	Cl/CN	dmso	–	[46]
88	POMTUJ	2D-dist.hex	Yb	Cl/CN	dmso	–	[37]
89	POMVAR	2D-dist.hex	Yb/Er	Cl/CN	dmso	–	[37]
100	1944127	2D-brickwall	Yb	Cl	H2O	–	[45]
103	LUTRIE	2D-brickwall	Yb	Br	H2O	–	[55]
111	QOVJUJ	2D-brickwall	Yb	Cl/CN	dmso/dobdc2−	–	[56]
112	QOVJOD	2D-brickwall	Yb	Cl/CN	dmso/F4bdc2−	–	[56]
127	XIKNUD	2D-herringbone	Yb	Cl/CN	dmf	–	[48]
137	QOFNEH	2D-4,4	Yb	Cl	–	NEt4+	[57]

) and three with Lu(III) (

Table 27. Structurally characterized Lu(III) compounds with anilato ligands.

#	CCDC	Structure	Ln	X	L	A+	Reference
33	MIZZUQ	1D + mon	Lu	Cl	H2O	–	[16]
39	MIZXOI	2D-hex	Lu	H	H2O	–	[16]
141	QOFPEJ	2D-4,4	Lu	Cl	–	NEt4+	[57]

).

3. Magnetic Properties

Single-Molecule and Single-Ion Magnets

Most of the magnetically characterized Ln-anilato compounds show the expected magnetic properties of isolated Ln(III) ions with the corresponding decrease in the χ_mT product when the temperature is decreased as a result of the depopulation of the excited levels that appear due to the ligand field. This behaviour confirms the absence of noticeable magnetic interactions through the anilato bridges when connecting Ln(III) ions. In fact, only when connecting transition metals, anilato bridges show weak antiferromagnetic interactions (that can be modulated by the X group) [6,61]. Although this lack of magnetic interactions may appear as a disadvantage from the magnetic point of view, the good magnetic isolation provided by the anilato ligands precludes the fast relaxation of the magnetization and allows the synthesis of Ln-anilato complexes and coordination polymers behaving as single-molecule magnets (SMMs) and single-ion magnets (SIMs) with slow relaxation of the magnetization. SMMs and SIMs are attracting many interest recently since they present memory effects and quantum phenomena that may find applications in data storage, quantum computing and spintronics [62,63,64]. SMMs and SIMs retain their spin orientation and show a slow relaxation of the magnetization at low temperatures that may follow different mechanisms such as: (i) Orbach (O), (ii) Raman (R), (iii) direct (D) and (iv) quantum tunnelling (QT). The O, R and D mechanisms are temperature dependent and the D and QT mechanisms are field dependent [62,63,64]. Usually, when several mechanisms are operative, the relaxation time is determined by the faster process and, thus, QT is operative at low temperatures (when no DC field is applied), whereas Orbach mechanism is the dominant one at high temperatures. In some cases, the application of a DC field (usually below 3000 Oe) suppress the fast relaxation through the QT mechanism. In these compounds, called field-induced-SMM of field induced-SIM (FI-SMM or FI-SIM), the application of a DC field is required to observe the slow relaxation of the magnetization and the direct mechanism may contribute to the relaxation of the magnetization. The equation used to reproduce the relaxation rate (the inverse of the relaxation times, τ) as a function of the temperature and/or DC field includes the O, R, D and QT mechanisms as follow [62,63,64]:

$${\tau }^{-1}={\tau }_0^{-1}exp\left(\frac{-U_{eff}}{k_{B}T}\right)+C{T}^n+A{H}^{2}T+{\tau }_{QTM}^{-1}.$$

(1)

Surprisingly, the possibility to prepare Ln-anilato-based SMMs and SIMs has not been exploited until very recently (Table 28). Thus, the first Ln-anilato complexes showing SMM behaviour were reported in 2017 by Boskovic et al. in two closely related Dy(III) dimers [(Tp)₂Dy₂(C₆O₄Cl₂)]·2CH₂Cl₂ (4) and [(Tp)₂Dy₂(C₆O₄(CH₃)₂)]·1.1CH₂Cl₂ (4′) (Tp^- = hydrotris(pyrazolyl)borate = HB(pz)₃) [20]. Although only the structure of compound 4 was reported, compound 4′ is isostructural to the Y analogue [(Tp)₂Y₂(C₆O₄(CH₃)₂)]·1.2CH₂Cl₂ (11) [20]. Compound 4′ shows an almost temperature independent slow relaxation of the magnetization that follows a quantum tunnelling mechanism when no DC field is applied at low temperatures and when a DC field of 1600 Oe is applied, both compounds (4 and 4′) show slow relaxation of the magnetizations with an Orbach relaxation mechanism for 4′ with U_eff = 47 K and Orbach and Raman mechanisms for 4 with U_eff = 24 K [20].

Compound [(Tp)₂Dy₂(C₆O₄Cl₂)]·2CH₂Cl₂ (4) was almost simultaneously reported twice more (compounds 5 and 6 in Table 28) by Slageren et al. [22] and by Ishikawa et al. [19]. Both reports confirm the FI-SMM behaviour of compound 4 and complete the magnetic studies with different applied DC fields and temperature ranges. Furthermore, Slageren et al. [22] showed that when the chloranilato bridge is chemically reduced using cobaltocene, the Dy and Tb dimers (4 and 24, respectively) behave as SMM even with no applied DC field. Slageren also showed that when a DC field of 1000 Oe is applied, the reduced Dy derivative shows two different relaxation processes [22]. The energy barriers obtained by Slageren et al., even when the choranilato bridge was reduced, are similar to those obtained by Boskovic et al. [20] (Table 28). The third study, made by Ishikawa et al. [19], was performed with a DC field of 950 Oe and also showed a similar energy barrier for the high temperature data although now the relaxation times was fit to a model including only Raman and Direct mechanisms [19]. In this study, Ishikawa et al. also reported the monomer [Co(Cp)₂][Dy(Tp)₂(C₆O₄Cl₂)] (1), that also behaves as a FI-SMM with an energy barrier of 49.4 K when a DC field of 1500 Oe is applied. Under this DC field, the relaxation of the magnetization of compound 1 follows Raman and Direct mechanisms [19].

Boskovic et al. [23] reported in 2019 a similar dimer to compound 4 but prepared with bromanilato instead of chloranilato: [(Tp)₂Dy₂(C₆O₄Br₂)] (18). Compound 18 is also a FI-SMM and presents a low energy barrier of 7 K when a DC field of 390 Oe is applied. As observed in dimer 4, when the bromanilato bridge in dimer 18 is reduced, the compound behaves as a SMM with zero applied DC field. The reduced dimer 18 also shows low energy barriers of 10.4 and 10.6 K for DC fields of 0 and 380 Oe, respectively. In all cases, the relaxation of the magnetization follows Orbach, Raman and direct mechanisms [23].

In addition, in 2019, Ishikawa et al. [24] reported the Er and Yb derivatives with chloranilato (compounds 22 and 29, respectively, Table 28). Both compounds behave as FI-SMM and show energy barriers of 25.9 and 22.3 K, respectively, when a DC field of 1000 Oe is applied. In both cases, the relaxation times can be very well reproduced using Orbach and Raman mechanisms [24].

As can be seen in Table 28, all the above-mentioned SMM and FI-SMM complexes contain the coligand (Tp^- = hydrotris(pyrazolyl)borate = HB(pz)₃). The only reported dimer with SMM behaviour without the Tp^- coligand is compound [Eu_1.96Dy_0.04(C₆O₄(CN)Cl)₃(H₂O)₁₀]·6H₂O (31) [27]. This dimer shows a zigzag structure (Figure 2d) and contains a bridging chlorocyananilato ligand. Compound 31 is also the only doped dimer with SMM behaviour (contains Eu doped with 2% of Dy) and is also the only Ln-anilato dimer showing SMM without applying a DC field or reducing the bridging anilato ligand. This compound presents an energy barrier of 25.3 K and the relaxation of the magnetization could be fit to an Orbach and Direct mechanisms, although in this case, the frequency maxima appear at high frequencies and could not be observed [27].

Besides these discrete complexes (nine dimers and one monomer, Table 28), there are also six Ln-anilato 2D lattices showing FI-SMM or even SMM (in one case). Two of these six 2D lattices are isostructural 4,4-nets showing FI-SMM behaviour: (NEt₄)[Dy(C₆O₄Cl₂)₂] (135) and (NEt₄)[Gd(C₆O₄Cl₂)₂] (136) [57]. In both cases, the measurements were performed with a DC field of 1000 Oe, although no analysis of the relaxation mechanisms nor the energy barrier was reported [57]. The observation of slow relaxation in compound 136 is very surprising since Gd(III) is an isotropic ion and is very unusual to observe SMM or FI-SMM behaviour in Gd(III) complexes [65]. The exact mechanism to explain this unusual behaviour is not clear yet.

The four remaining 2D lattices showing slow relaxation of the magnetization are 3,6-networks (Table 28). Three of them contain Dy(III) and bromanilato: [Dy₂(C₆O₄Br₂)₃(H₂O)₆]·8H₂O (80) [45,55], [Dy₂(C₆O₄Br₂)₃(dmso)₄]·2dmso·2H₂O (83) [51,55] and [Dy₂(C₆O₄Br₂)₃(dmf)₆] (125) [55], whereas the fourth one contains Eu doped with Dy: [Dy_0.04Eu_1.96(C₆O₄Br₂)₃(dmso)₆]·2dmso (123) [27]. Compounds 80, 83 and 125 are three closely related compounds that, in fact, show reversible interconversion upon solvent exchange (see below) [55]. Compounds 80 and 83 show distorted hexagonal 2D lattices whereas compound 125 shows a rectangular herringbone 2D structure. Compounds 80 and 83 show slow relaxation of the magnetization under a DC field of 1000 Oe (Figure 22a), with energy barriers of 9.6 and 22.8 K, respectively (Figure 22b).

The relaxation of the magnetization follows an Orbach mechanism in compound 80, whereas in compound 83 it follows Orbach, direct and quantum tunnelling mechanisms. Since both compounds show the same structure, Ln(III) ion and ligand, we can attribute these differences to the changes in the coordination geometry of the Dy(III) ions (TCTPR-9 in 80 vs. TDD-8 in 83). These changes in the coordination number and geometry are due to the different sizes of the coligands (H₂O in 80 vs. dmso in 83). Despite showing a different structure, compound 125 is closely related to compounds 80 and 83 (the only difference is that it contains dmf as coligand, instead of H₂O or dmso). Compound 125 also shows slow relaxation of the magnetization when a DC field of 1000 Oe is applied (Figure 22a), although now there are two different relaxation processes: (i) a slow relaxation process (SR) with an energy barrier of 36 K and a relaxation following Orbach and direct mechanisms and (ii) a fast relaxation (FR) process with an energy barrier of 11.4 K that relaxes following an Orbach mechanism (Figure 22b) [55]. Finally, compound 123 is the only 2D lattice showing slow relaxation of the magnetization with zero applied DC field. This compound shows an energy barrier of 40.9 K [27].

Table 28. Ln-anilato compounds with slow relaxation of the magnetization.

#	CCDC	Structure	Ln	X	Geometrya	A+	L b	H (Oe)	Ueff (K)	Rel. Mec. c	Reference
1	PIQFUT	Mon.	Dy	Cl	SAPR-8	–	Tp-	1500	49.4	R/D	[19]
4	DEKTOF	Dimer	Dy	Cl	TDD-8	–	Tp-	1600	24	O/R	[20]
4′	-	Dimer	Dy	CH3	TDD-8	–	Tp-	1600	47	O	[20]
5	DEKTOF01	Dimer	Dy	Cl	TDD-8	–	Tp-	1000 1000 0	39 31 e SMM e	O O O	[22]
6	DEKTOF02	Dimer	Dy	Cl	TDD-8	–	Tp-	950	44.7	R/D	[19]
18	JOQSEQ	Dimer	Dy	Br	TDD-8	–	Tp-	390 0 380	7 10.4 e 10.6 e	O/R/D O/R/D O/R/D	[23]
22	KOZBEJ	Dimer	Er	Cl	TDD-8	–	Tp-	1000	25.9	O/R	[24]
24	LEPNIG	Dimer	Tb	Cl	TDD-8	–	Tp-	0	SMM e	–	[22]
29	OBIBEH01	Dimer	Yb	Cl	TDD-8	–	Tp-	1000	22.3	O/R	[24]
31	NOQGEI	Dimer-zz	Eu/Dy d	Cl/CN	CSAPR-9	–	H2O	0	25.3	O/D	[27]
80	1565279	2D-hex	Dy	Br	TCTPR-9	–	H2O	1000	9.6	O	[45,55]
83	NIDFUE	2D-hex	Dy	Br	TDD-8	–	dmso	1000	22.8	O/D/QT	[51,55]
123	NOQBON	2D-herr	Eu/Dy d	Br	CSAPR-9	–	dmso	0	40.9	O/D	[27]
125	LUTROK	2D-herr	Dy	Br	CSAPR-9	–	dmf	1000	11.4 (FR) 36 (SR)	O O/D	[55]
135	QOFCEW	2D-4,4	Dy	Cl	SAPR-8	NEt4+	–	SMM	–	–	[57]
136	QOFNAD	2D-4,4	Gd	Cl	SAPR-8	NEt4+	–	SMM	–	–	[57]

(^a) The geometry was determined with the program SHAPE [29,30,31,32,33,34,35,36]. SAPR-8 = square antiprism, TDD-8 = triangular dodecahedron, CSAPR-9 = capped square antiprism; (^b) Tp^- = HB(pz)₃⁻ = hydrotris(pyrazolyl)borate, dmso = dimthylsulfoxide, dmf = dimethylformamide; (^c) relaxation mechanism of the magnetization: O = Orbach, R = Raman, QT = quantum tunnelling, D = direct (^d) Eu (98%)/Dy (2%); (^e) data with the anilato bridge reduced.

Table 28. Ln-anilato compounds with slow relaxation of the magnetization.

#	CCDC	Structure	Ln	X	Geometrya	A+	L b	H (Oe)	Ueff (K)	Rel. Mec. c	Reference
1	PIQFUT	Mon.	Dy	Cl	SAPR-8	–	Tp-	1500	49.4	R/D	[19]
4	DEKTOF	Dimer	Dy	Cl	TDD-8	–	Tp-	1600	24	O/R	[20]
4′	-	Dimer	Dy	CH3	TDD-8	–	Tp-	1600	47	O	[20]
5	DEKTOF01	Dimer	Dy	Cl	TDD-8	–	Tp-	1000 1000 0	39 31 e SMM e	O O O	[22]
6	DEKTOF02	Dimer	Dy	Cl	TDD-8	–	Tp-	950	44.7	R/D	[19]
18	JOQSEQ	Dimer	Dy	Br	TDD-8	–	Tp-	390 0 380	7 10.4 e 10.6 e	O/R/D O/R/D O/R/D	[23]
22	KOZBEJ	Dimer	Er	Cl	TDD-8	–	Tp-	1000	25.9	O/R	[24]
24	LEPNIG	Dimer	Tb	Cl	TDD-8	–	Tp-	0	SMM e	–	[22]
29	OBIBEH01	Dimer	Yb	Cl	TDD-8	–	Tp-	1000	22.3	O/R	[24]
31	NOQGEI	Dimer-zz	Eu/Dy d	Cl/CN	CSAPR-9	–	H2O	0	25.3	O/D	[27]
80	1565279	2D-hex	Dy	Br	TCTPR-9	–	H2O	1000	9.6	O	[45,55]
83	NIDFUE	2D-hex	Dy	Br	TDD-8	–	dmso	1000	22.8	O/D/QT	[51,55]
123	NOQBON	2D-herr	Eu/Dy d	Br	CSAPR-9	–	dmso	0	40.9	O/D	[27]
125	LUTROK	2D-herr	Dy	Br	CSAPR-9	–	dmf	1000	11.4 (FR) 36 (SR)	O O/D	[55]
135	QOFCEW	2D-4,4	Dy	Cl	SAPR-8	NEt4+	–	SMM	–	–	[57]
136	QOFNAD	2D-4,4	Gd	Cl	SAPR-8	NEt4+	–	SMM	–	–	[57]

(^a) The geometry was determined with the program SHAPE [29,30,31,32,33,34,35,36]. SAPR-8 = square antiprism, TDD-8 = triangular dodecahedron, CSAPR-9 = capped square antiprism; (^b) Tp^- = HB(pz)₃⁻ = hydrotris(pyrazolyl)borate, dmso = dimthylsulfoxide, dmf = dimethylformamide; (^c) relaxation mechanism of the magnetization: O = Orbach, R = Raman, QT = quantum tunnelling, D = direct (^d) Eu (98%)/Dy (2%); (^e) data with the anilato bridge reduced.

4. Optical Properties

Besides magnetic properties, all these Ln-anilato compounds may also show interesting optical properties, such as luminescence, very common in many Ln-containing compounds [66]. Furthermore, some anilato ligands such as chlorocyananilato and nitranilato, may also show luminescence in solid state [26,67] and in solution [68,69], even when they are not coordinated. Table 29 shows all the structurally characterized Ln-anilato compounds showing luminescence with the corresponding ligand- and lanthanoid-based emission bands.

The first luminescence study on a Ln-anilato compound (and the only one with chloranilato) dates back to 2004 when Kaizaki et al. [25] performed a study of the Yb(III) dimer: [(YbTp)₂(C₆O₄Cl₂)]·2CH₂Cl₂ (28). This compound shows a strong 4f-4f emission at ca. 1000 nm attributed to ligand-to-metal energy transfer from the triplet state of the chloranilato ligand to the excited 4f state of the Yb(III) ion [25]. The strong absorption band at 560 nm observed in this compound was attributed to the chloranilato ligand. In contrast, the analogue dimers with Tb(III) or Eu(III) did not show any emission, suggesting the presence of a back-transfer from the Ln(III) ions to the chloranilato ligand [25].

The other dimers showing luminescence, [Ln₂(C₆O₄(NO₂))₃(H₂O)₁₀]·6H₂O with Ln = Gd (13), Tb (14), Dy (15), Ho (16) and Sm (17) were reported in 2016 [26]. These dimers show the emission of the nitranilato ligand, centered at ca. 590 nm. In contrast to compounds 13-15 and 17, where the anilato ligand does not sensitize the emission of the Ln(III) ions, in compound 16 there are two emission bands from the Ho(III) ions at 531 and 643 nm, attributed to the ⁵F₄ → ⁵I₈ and ⁵F₅ → ⁵I₈ transitions, respectively [26]. Besides dimers, luminescence has also been very recently observed in some 2D Ln-anilato lattices. The first observation of luminescence in 2D lattices was reported in a chlorocyananilato lattice with Yb(III): [Yb₂(C₆O₄(CN)Cl)₃(dmso)₄]·2H₂O (87) [46]. This compound shows the emission of the chlorocyananilato ligand at around 700 nm (Figure 23a), with a red shift of ca. 25 nm when compared with the free ligand in the solid K₂(C₆O₄(CN)Cl) salt. Besides the ligand emission, compound 87 shows the typical emission in the NIR, at ca. 980 nm, corresponding to the ²F_5/2 → ²F_7/2 transition of the Yb(III) ion (Figure 23b) [46]. The related 2D lattices [Pr₂(C₆O₄(CN)Cl)₃(dmso)₆] (104) and [Pr₂(C₆O₄(CN)Cl)₃(dmf)₆] (126) also show the ligand emission at ca. 700 and 680 nm, respectively (although much weaker in 104), but no emission from the Ln(III) ions could be observed [46].

Table 29. Ln-anilato complexes and lattices with anilato-based and/or Ln-based luminescence.

#	CCDC	Structure	Ln	X	Anilato (nm)	Ln(III) (nm)	Reference
13	EDEZAR	Dimer	Gd	NO2	≈590	–	[26]
14	EDEZEV	Dimer	Tb	NO2	≈590	–	[26]
15	EDEZIZ	Dimer	Dy	NO2	≈590	–	[26]
16	EDEZOF	Dimer	Ho	NO2	596	531, 643	[26]
17	EDEZUL	Dimer	Sm	NO2	≈590	–	[26]
28	OBIBEH	Dimer	Yb	Cl	560	≈1000	[25]
53	XIKNOX	2D-hex	Nd	Cl/CN	≈650 ≈460 a 680–720 b	900, 1070, 1350	[48]
54	XIKPAL	2D-hex	Er	Cl/CN	≈650 ≈460 a 680–720 b	≈1550	[48]
80	1565279	2D-hex	Dy	Br	–	≈500	[55]
83	NIDFUE	2D-hex	Dy	Br	–	≈500	[55]
87	DIFLUC	Distorted 2D-hex	Yb	Cl/CN	≈700	980	[46]
88	POMTUJ	Distorted 2D-hex	Yb	Cl/CN	–	980	[37]
89	POMVAR	Distorted 2D-hex	Yb/Er	Cl/CN	–	980 1530	[37]
104	DIFLOW	2D-brick wall	Pr	Cl/CN	≈680	–	[46]
111	QOVJUJ	2D-brick wall	Yb	Cl/CN	650–900	≈1000	[56]
112	QOVJOD	2D-brick wall	Yb	Cl/CN	650–900	≈1000	[56]
125	LUTROK	2D-herr	Dy	Br	–	≈500	[55]
126	DIFLIQ	2D-herringbone	Pr	Cl/CN	≈680	–	[46]
127	XIKNUD	2D-herringbone	Yb	Cl/CN	≈650 ≈460 a 680–720 b	≈980	[48]
149	POMVIZ	2D-(3,4)+(3,8)	Er	Cl/CN	710	1530	[37]

(^a) Nanosheets suspension; (^b) drop-casted nanosheets.

Table 29. Ln-anilato complexes and lattices with anilato-based and/or Ln-based luminescence.

#	CCDC	Structure	Ln	X	Anilato (nm)	Ln(III) (nm)	Reference
13	EDEZAR	Dimer	Gd	NO2	≈590	–	[26]
14	EDEZEV	Dimer	Tb	NO2	≈590	–	[26]
15	EDEZIZ	Dimer	Dy	NO2	≈590	–	[26]
16	EDEZOF	Dimer	Ho	NO2	596	531, 643	[26]
17	EDEZUL	Dimer	Sm	NO2	≈590	–	[26]
28	OBIBEH	Dimer	Yb	Cl	560	≈1000	[25]
53	XIKNOX	2D-hex	Nd	Cl/CN	≈650 ≈460 a 680–720 b	900, 1070, 1350	[48]
54	XIKPAL	2D-hex	Er	Cl/CN	≈650 ≈460 a 680–720 b	≈1550	[48]
80	1565279	2D-hex	Dy	Br	–	≈500	[55]
83	NIDFUE	2D-hex	Dy	Br	–	≈500	[55]
87	DIFLUC	Distorted 2D-hex	Yb	Cl/CN	≈700	980	[46]
88	POMTUJ	Distorted 2D-hex	Yb	Cl/CN	–	980	[37]
89	POMVAR	Distorted 2D-hex	Yb/Er	Cl/CN	–	980 1530	[37]
104	DIFLOW	2D-brick wall	Pr	Cl/CN	≈680	–	[46]
111	QOVJUJ	2D-brick wall	Yb	Cl/CN	650–900	≈1000	[56]
112	QOVJOD	2D-brick wall	Yb	Cl/CN	650–900	≈1000	[56]
125	LUTROK	2D-herr	Dy	Br	–	≈500	[55]
126	DIFLIQ	2D-herringbone	Pr	Cl/CN	≈680	–	[46]
127	XIKNUD	2D-herringbone	Yb	Cl/CN	≈650 ≈460 a 680–720 b	≈980	[48]
149	POMVIZ	2D-(3,4)+(3,8)	Er	Cl/CN	710	1530	[37]

(^a) Nanosheets suspension; (^b) drop-casted nanosheets.

A recent study by Mercuri et al. [37] of two related series, also with the ligand chlorocyananilato and dmso as solvent, formulated as [Ln₂(C₆O₄(CN)Cl)₃(dmso)₄]·dmso, with Ln = Yb (88), Yb/Er (89) and [Er₂(C₆O₄(CN)Cl)₃(dmso)₆] (149) [37], showed similar results, further confirming the antenna effect of the chlorocyananilato ligand and the Ln-based emission in the NIR region. Thus, compounds 88 and 89 show an emission band at 980 nm, corresponding to the ²F_5/2 → ²F_7/2 transition in the Yb(III) ions and compounds 89 and 149 show an emission band at 1530 nm, corresponding to the ⁴I_13/2 → ⁴I_15/2 transition in the Er(III) ions [37]. These compounds show high quantum yields of 15.6% for the Yb(III) compound and 0.16% for the Er(III) one, the highest reported for coordination compounds to date. Remarkably, these properties are retained in dmso solutions and in drop-casted films [37].

A very interesting report also by Mercuri et al. [48] showed NIR emission in a family of three 2D lattices formulated as [Ln₂(C₆O₄(CN)Cl)₃(dmf)₆]·G with Ln/G = Nd/2CH₂Cl₂ (53), Er/2CH₂Cl₂ (54) and Yb/- (127). These layered compounds show the emission of the chlorocyananilato ligand at around 650 nm (with a red shift of ca. 50 nm when compared with the free ligand in the solid KH(C₆O₄(CN)Cl) salt). Besides the ligand emission, the three compounds show the Ln(III) emission at ca. 900, 1070 and 1350 nm in 53, ca. 1550 nm in 54 and ca. 980 nm in 127, showing the antenna effect of the chlorocyananilato ligand [48]. The measurements performed on suspensions of nanosheets of these compounds show that the emission of the Ln(III) ions are similar to those of the crystals but the ligand emission appears blue-shifted at ca. 460 nm, close to the value observed for the free ligand in dilute solution. When these nanosheets are drop-casted, the Ln(III) emission remains unchanged but the ligand emission appears at ca. 680-720 nm, close to the value observed in the crystals [48].

A similar study has very recently been performed by the same team on two original Ln-anilato 2D lattices including additional coligands such as the dianion of 2,5-dihydroxybenzene-1,4-dicarboxylic acid (H₂dobdc): [Yb₄(C₆O₄(CN)Cl)₅(dobdc)(dmso)₁₀]·2dmso (111) and the dianion of 2,3,5,6-tetrafluorobenzene-1,4-dicarboxylic acid (H₂F₄bdc): [Yb₂(C₆O₄(CN)Cl)₂(F₄bdc)(dmso)₆] (112) [56]. These two compounds show a very broad emission from ca. 650 nm to more than 900 nm attributed to the chlorocyananilato ligand together with a much stronger emission at ca. 1000 nm from the Yb(III) ions, showing once more the antenna effect of the ligand. Studies performed on nanosheets of compounds 111 and 112 show similar photoluminescence spectra although with much weaker signals [56].

Finally, luminescence has also been reported [55] in three related 2D latices formulated as [Dy₂(C₆O₄Br₂)₃(H₂O)₆]·8H₂O (80), [Dy₂(C₆O₄Br₂)₃(dmso)₄]·2dmso·2H₂O (83) and [Dy₂(C₆O₄Br₂)₃(dmf)₆] (125) that can be easily interconverted by solvent exchange and that also show FI-SMM behaviour (see above). These three compounds show an increase in the emission of the Dy(III) ion when changing the solvent from dmf (where the emission is almost completely quenched) to H₂O and dmso [55].

5. Gas/Solvent Adsorption/Absorption and Solvent Exchange

Very recently, gas and solvent adsorption and even solvent exchange have been reported in some Ln-anilato compounds (

Table 30. Ln-anilato compounds with gas/solvent adsorption or solvent exchange capacity.

#	Formula	Ln	Structure	Properties	Reference
35–38 41–49	[Ln2(dhbq)3(H2O)6]·18H2O	La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb	2D-hexagonal	−H2O/+H2O −H2O/+Guess CO2 adsorption	[45]
58–60 62, 64–70	[Ln2(C6O4Cl2)3(H2O)6]·nH2O	La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er	Distorted 2D-hex.	−H2O/+H2O −H2O/+Guess CO2 adsorption	[45]
71–81	[Ln2(C6O4Br2)3(H2O)6]·nH2O	La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er	Distorted 2D-hex.	−H2O/+H2O −H2O/+Guess CO2 adsorption	[45]
80	[Dy2(C6O4Br2)3(H2O)6]·8H2O	Dy	2D-brickwall	Solv Exch.	[55]
83	[Dy2(C6O4Br2)3(dmso)6]·2dmso	Dy	Distorted 2D-hex.	Solv Exch.	[55]
125	[Dy2(C6O4Br2)3(dmf)6]	Dy	2D-herringbone	Solv Exch.	[55]
92	[La2(C6O4(t-Bu)2)3(dma)4]	La	Distorted 2D-hex.	CO2 abs	[52]
93	[Pr2(C6O4(t-Bu)2)3(dma)4]	Pr	Distorted 2D-hex.	CO2 abs	[52]
94	[Nd2(C6O4(t-Bu)2)3(dma)4]	Nd	Distorted 2D-hex.	CO2 abs	[52]
99–100	[Ln2(C6O4Cl2)3(H2O)6]·nH2O	Tm, Yb	2D-brickwall	−H2O/+H2O −H2O/+Guess	[45]
102–103	[Ln2(C6O4Br2)3(H2O)6]·nH2O	Tm, Yb	2D-brickwall	−H2O/+H2O −H2O/+Guess	[45]
131	(NEt4)[Y(C6O4Cl2)2]·1.4CS2	Y	2D-4,4	1.4 CS2 abs	[57]
132	(NEt4)[Y(C6O4Cl2)2]	Y	2D-4,4	N2/H2/CO2/CH4	[57]
133	(NEt4)[Y(C6O4Cl2)2]·1.9I2	Y	2D-4,4	1.9 I2 abs	[57]
134	(NEt4)[Y(C6O4Cl2)2]·0.9Br2	Y	2D-4,4	0.9 Br2 abs	[57]

). The first observation of gas adsorption in a Ln-anilato compound was reported in the series [Ln₂(dhbq)₃(H₂O)₆]·18H₂O with Ln(III) = Ho (35), La (36), Gd (37), Yb (38), Lu (39), Y (40), Er (41), Ce (42), Pr (43), Nd (44), Sm (45), Eu (46), Tb (47), Dy (48) and Tm (49) [45]. As described above (Figure 6d), this series contains a cluster of 18 water molecules, plus six crystallization extra water molecules, that can be easily removed when the samples are heated to 80 °C or simply under vacuum at room temperature (the total number of removed water molecules oscillates between 18 and 22) [45]. The removal of the water molecules leads to a colour change of the samples and to an almost complete collapse of the structure, as shown by the X-ray powder diffraction of the evacuated samples (Figure 24a). Studies of the reversibility of this process showed that it is fully reversible and when the dehydrated samples are immersed in water, they recover the original structure (Figure 24a). Moreover, when the dehydrated samples are immersed in different solvents, these solvents enter in the interlayer space and, in some cases, the samples recover the crystallinity, although the new structure is not the same as the hydrated pristine sample (Figure 24b).

The evacuation of the water molecules in compounds 35-38 and 41-49 leaves empty hexagonal cavities where, besides other solvents, it is also possible to insert gases (Figure 25a). Thus, the dehydrated compounds show CO₂ uptake with a maximum of ca. one CO₂ molecule per hexagonal cavity at 0 °C and 100 kPa (Figure 25b) [45].

Similar results have also been observed in the corresponding series with chloranilato, formulated as [Ln₂(C₆O₄Cl₂)₃(H₂O)₆]·nH₂O, with Ln(III) = Pr (58), Nd (59), Tb (60), Ce (61 and 62), Y (63), Gd (64), Eu (65), Er (66), La (67), Sm (68), Dy (69), Ho (70), Tm (99) and Yb (100) [45] and with bromanilato, formulated as [Ln₂(C₆O₄Br₂)₃(H₂O)₆]·nH₂O with Ln/n = La/9 (72), Ce/8 (73), Pr/11 (74), Nd/7 (75), Sm/10 (76), Eu/6 (77), Gd/8 (78), Tb/10 (79), Dy/8 (80), Ho/10 (81), Er/7 (71), Tm/5.5 (102) and Yb/3.5 (103) [45]. The main difference is that in these two series, the structure does not collapse upon dehydration (only some reflections are lost), probably because now, in contrast with the dhbq²⁻ series, the water molecules do not play any structural role since they are located in the distorted hexagonal or rectangular cavities and in the interlayer space.

There are two other very recently published studies showing gas/solvent uptake in Ln-anilato compounds [52,57]. The first one is a very interesting study performed on compound (NEt₄)[Y(C₆O₄Cl₂)₂] (132), a square 2D-4,4 anionic lattice (Figure 16f) that shows reversible CS₂, I₂ and Br₂ uptake, while keeping the crystallinity [57]. This uptake capacity has allowed the synthesis of compounds (NEt₄)[Y(C₆O₄Cl₂)₂]·nG with nG = 1.43 CS₂ (131), 1.87 I₂ (133) and 0.91 Br₂ (134) [57]. Additionally, compound 132 can also uptake N₂, H₂, CO₂ and CH₄ in its square channels, with high binding enthalpies, among the highest reported for porous coordination polymers, as clearly evidenced by the corresponding adsorption isotherms and by a neutron diffraction study that allowed to determine the location of the adsorbed molecules and their interactions with the lattice [57].

The second study has been published very recently for compounds [Ln₂(C₆O₄(t-Bu)₂)₃(dma)₄] with Ln = La (92), Pr (93) and Nd (94) (Figure 11c). As expected, given the bulky t-Bu groups in the anilato ligands, this study has shown a low porosity with CO₂ adsorption isotherms typical of microporous materials [52].

Finally, we have very recently reported three examples of direct solvent exchange without the need to evacuate the pristine compounds [55]. This study shows that it is possible to exchange the solvent molecules, even the coordinated ones, by immersing compounds [Dy₂(C₆O₄Br₂)₃(H₂O)₆]·8H₂O (80), [Dy₂(C₆O₄Br₂)₃(dmf)₆] (83), or [Dy₂(C₆O₄Br₂)₃(dmso)₄]·2dmso·2H₂O (125) in any of the two other solvents (Figure 26). Interestingly, the three compounds present slow relaxation of the magnetization with different relaxation mechanisms and relaxation times (Table 28) that can be easily modified by simple immersion in the desired solvent [55].

6. Redox Studies

An additional interesting aspect of the anilato ligands is the possibility to be chemically or electrochemically reduced by one or two electrons to form the semiquinoid and cathecolato forms, respectively (Scheme 1b). This possibility has been studied in several of the reported dimers in order to try to increase the magnetic exchange through the anilato bridge and to improve the SMM properties of these dimers. Interestingly, all the reported compounds with reduced anilato bridges are dimers and have been reported in the last three years (Table 31).

The first reduction study was performed by Molainen et al. [21] in compounds [Ln₂(C₆O₄H₂)(thf)₆Cl₄]; Ln = Dy (2) and Y (3) (Figure 2a). This study showed a one electron reduction process in the dhbq²⁻ bridge in both compounds to generate the radical (dhbq³⁻)· that could be easily detected with electron paramagnetic resonance (EPR) spectroscopy. In this report, both compounds could be reduced electrochemically and chemically using tetrakis-(dimethylamino)ethylene (TDAE) as reducing agent [21].

A second study, published almost simultaneously, by Boskovic et al. [20] on compounds [(LnTp)₂(C₆O₄X₂)]·G with Ln/X/G = Dy/Cl/2CH₂Cl₂ (4), Y/Cl/2CH₂Cl₂ (7), Y/Cl/2Me₂CO (9), Y/CH₃/1.2CH₂Cl₂ (11) and Y/CH₃/4.5MeOH (12) shows two reduction processes (one reversible and one quasi-reversible) and one oxidation irreversible process in the cyclic voltammetry. Attempts to chemically reduce the chloranilate derivatives 4, 7 and 9 with cobaltocene in anaerobic and anhydrous conditions led to a colour change from purple to green, indicative of a chemical reduction, but the reduced compounds could not be isolated [20].

A third study, published a few months later on the closely related compounds [(LnTp)₂(C₆O₄X₂)]·G with Ln/X/G = Dy/Cl/2CH₂Cl₂ (5), Y/Cl/2CH₂Cl₂ (8), Tb/Cl/2CH₂Cl₂ (24) and Gd/Cl/2CH₂Cl₂ (26) [22] showed very similar results to those previously reported on the same series of compounds although now, the authors were able to prepare the reduced products with cobaltocene as cation and could measure an antiferromagnetic coupling of −4.17 cm⁻¹ in the Gd(III) derivative, confirming that the magnetic coupling is much higher when the anilato bridge is in its radical semiquinone form [22].

Finally, a more recent cyclic voltammetry study performed on the series of dimers [(LnTp)₂(C₆O₄Br₂)]·2CH₂Cl₂ with Ln = Dy (18) and Y (21) [23] also shows the presence of one reversible and one quasi-reversible reduction processes and one irreversible oxidation process in both compounds. As in other similar examples, compounds 18 and 21 could also be reduced chemically with cobaltocene, although only amorphous solids could be isolated [23].

Table 31. Ln-anilato compounds with reduced anilato ligands.

#	CCDC	Structure	Ln	X	Redox processes	Reductant a	Reference
2	DEHQUF	Dimer	Dy	H	1 red.	Electrochem/TDAE	[21]
3	DEHRAM	Dimer	Y	H	1 red.	Electrochem/TDAE	[21]
4	DEKTOF	Dimer	Dy	Cl	2 red./1 oxid.	Electrochem/Co(Cp)2	[20]
5	DEKTOF01	Dimer	Dy	Cl	2 red.	Electrochem/Co(Cp)2	[22]
7	DEKTUL	Dimer	Y	Cl	2 red./1 oxid.	Electrochem/Co(Cp)2	[20]
8	DEKTUL01	Dimer	Y	Cl	2 red.	Electrochem/Co(Cp)2	[22]
9	DEKVAT	Dimer	Y	Cl	2 red./1 oxid.	Electrochem/Co(Cp)2	[20]
11	DEKVIB	Dimer	Y	CH3	2 red./1 oxid.	Electrochem.	[20]
12	DEKVOH	Dimer	Y	CH3	2 red./1 oxid.	Electrochem.	[20]
18	JOQSEQ	Dimer	Dy	Br	2 red./1 oxid.	Electrochem/Co(Cp)2	[23]
21	JOQSUG	Dimer	Y	Br	2 red./1 oxid.	Electrochem/Co(Cp)2	[23]
24	LEPNIG	Dimer	Tb	Cl	2 red.	Electrochem/Co(Cp)2	[22]
26	LEPNOM	Dimer	Gd	Cl	2 red.	Electrochem/Co(Cp)2	[22]

(^a) TDAE = tetrakis-(dimethylamino)ethylene; Co(Cp)₂ = cobaltocene.

Table 31. Ln-anilato compounds with reduced anilato ligands.

#	CCDC	Structure	Ln	X	Redox processes	Reductant a	Reference
2	DEHQUF	Dimer	Dy	H	1 red.	Electrochem/TDAE	[21]
3	DEHRAM	Dimer	Y	H	1 red.	Electrochem/TDAE	[21]
4	DEKTOF	Dimer	Dy	Cl	2 red./1 oxid.	Electrochem/Co(Cp)2	[20]
5	DEKTOF01	Dimer	Dy	Cl	2 red.	Electrochem/Co(Cp)2	[22]
7	DEKTUL	Dimer	Y	Cl	2 red./1 oxid.	Electrochem/Co(Cp)2	[20]
8	DEKTUL01	Dimer	Y	Cl	2 red.	Electrochem/Co(Cp)2	[22]
9	DEKVAT	Dimer	Y	Cl	2 red./1 oxid.	Electrochem/Co(Cp)2	[20]
11	DEKVIB	Dimer	Y	CH3	2 red./1 oxid.	Electrochem.	[20]
12	DEKVOH	Dimer	Y	CH3	2 red./1 oxid.	Electrochem.	[20]
18	JOQSEQ	Dimer	Dy	Br	2 red./1 oxid.	Electrochem/Co(Cp)2	[23]
21	JOQSUG	Dimer	Y	Br	2 red./1 oxid.	Electrochem/Co(Cp)2	[23]
24	LEPNIG	Dimer	Tb	Cl	2 red.	Electrochem/Co(Cp)2	[22]
26	LEPNOM	Dimer	Gd	Cl	2 red.	Electrochem/Co(Cp)2	[22]

(^a) TDAE = tetrakis-(dimethylamino)ethylene; Co(Cp)₂ = cobaltocene.

7. Thin Films

Since most of the Ln-anilato compounds crystallize as neutral layers, with general formula [Ln₂(C₆O₄X₂)₃(L)_n], several recent attempts to delaminate these 2D materials in thin films with nanometric dimensions have been performed (Table 32). The aim is to prepare crystalline thin films with a few monolayers showing properties such as luminescence, gas adsorption, or solvent exchange, in order to prepare thin film devices with potential applications as sensors.

The first compounds that have been delaminated as nanometric thin films are the series [Ln₂(dhbq)₃(H₂O)₆]·18H₂O with Ln(III) = Ce (42), Nd (44), Eu (46) and Dy (48) [45]. These compounds were dispersed in different solvents such as acetone, methanol and ethanol and sonicated during ten minuntes to obtain suspensions with nanosheets showing the Tyndall effect that confirms the presence of nanosheets in the suspensions (Figure 27a). By simply drop-casting these suspensions, it was possible to prepare nanosheets with lateral dimensions of a few microns (Figure 27b) and thickness of a few nanometers, corresponding to a few monolayers (Figure 27c).

A similar procedure allowed the preparation of thin films with a few monolayers of one chloranilato: [Tm₂(C₆O₄Cl₂)₃(H₂O)₆]·8H₂O (99) and two bromanilato: [Ln₂(C₆O₄Br₂)₃(H₂O)₆]·nH₂O with Ln/n = Er/7 (71) and Sm/10 (76) compounds [45].

Table 32. Ln-anilato compounds prepared as thin films.

#	CCDC	Compound	Ln	X	Film thickness	Reference
42	ZOTTAD	[Ce2(dhbq)3(H2O)6]·18H2O	Ce	H	3–4 monolayers	[45]
44	1944110	[Nd2(dhbq)3(H2O)6]·18H2O	Nd	H	3–4 monolayers	[45]
46	1944112	[Eu2(dhbq)3(H2O)6]·18H2O	Eu	H	5–6 monolayers	[45]
48	1944114	[Dy2(dhbq)3(H2O)6]·18H2O	Dy	H	4–5 monolayers	[45]
99	1944126	[Tm2(C6O4Cl2)3(H2O)6]·8H2O	Tm	Cl	3–4 monolayers	[45]
71	XAWZUT	[Er2(C6O4Br2)3(H2O)6]·7H2O	Er	Br	6–7 monolayers	[45]
76	1565275	[Sm2(C6O4Br2)3(H2O)6]·10H2O	Sm	Br	4–5 monolayers	[45]
53	XIKNOX	[Nd2(C6O4(CN)Cl)3(dmf)6]·2CH2Cl2	Nd	Cl/CN	1–4 monolayers	[48]
54	XIKPAL	[Er2(C6O4(CN)Cl)3(dmf)6]·2CH2Cl2	Er	Cl/CN	1–4 monolayers	[48]
88	POMTUJ	[Yb2(C6O4(CN)Cl)3(dmso)4]·dmso	Yb	Cl/CN	–	[37]
89	POMVAR	[YbEr2(C6O4(CN)Cl)3(dmso)4]·dmso	Yb/Er	Cl/CN	–	[37]
111	QOVJUJ	[Yb4(C6O4(CN)Cl)5(dobdc)(dmso)10]·2dmso a	Yb	Cl/CN	1-5 monolayers	[56]
112	QOVJOD	[Yb2(C6O4(CN)Cl)2(F4bdc)(dmso)6] b	Yb	Cl/CN	1-5 monolayers	[56]
127	XIKNUD	[Yb2(C6O4(CN)Cl)3(dmf)6]	Yb	Cl/CN	1–4 monolayers	[48]
149	POMVIZ	[Er2(C6O4(CN)Cl)3(dmso)6]	Er	Cl/CN	–	[37]

(^a) dobdc²⁻ = dianion of 2,5-dihydroxybenzene-1,4-dicarboxylic acid; (^b) the dianion of 2,3,5,6-tetrafluorobenzene-1,4-dicarboxylic acid (H₂F₄bdc).

Table 32. Ln-anilato compounds prepared as thin films.

#	CCDC	Compound	Ln	X	Film thickness	Reference
42	ZOTTAD	[Ce2(dhbq)3(H2O)6]·18H2O	Ce	H	3–4 monolayers	[45]
44	1944110	[Nd2(dhbq)3(H2O)6]·18H2O	Nd	H	3–4 monolayers	[45]
46	1944112	[Eu2(dhbq)3(H2O)6]·18H2O	Eu	H	5–6 monolayers	[45]
48	1944114	[Dy2(dhbq)3(H2O)6]·18H2O	Dy	H	4–5 monolayers	[45]
99	1944126	[Tm2(C6O4Cl2)3(H2O)6]·8H2O	Tm	Cl	3–4 monolayers	[45]
71	XAWZUT	[Er2(C6O4Br2)3(H2O)6]·7H2O	Er	Br	6–7 monolayers	[45]
76	1565275	[Sm2(C6O4Br2)3(H2O)6]·10H2O	Sm	Br	4–5 monolayers	[45]
53	XIKNOX	[Nd2(C6O4(CN)Cl)3(dmf)6]·2CH2Cl2	Nd	Cl/CN	1–4 monolayers	[48]
54	XIKPAL	[Er2(C6O4(CN)Cl)3(dmf)6]·2CH2Cl2	Er	Cl/CN	1–4 monolayers	[48]
88	POMTUJ	[Yb2(C6O4(CN)Cl)3(dmso)4]·dmso	Yb	Cl/CN	–	[37]
89	POMVAR	[YbEr2(C6O4(CN)Cl)3(dmso)4]·dmso	Yb/Er	Cl/CN	–	[37]
111	QOVJUJ	[Yb4(C6O4(CN)Cl)5(dobdc)(dmso)10]·2dmso a	Yb	Cl/CN	1-5 monolayers	[56]
112	QOVJOD	[Yb2(C6O4(CN)Cl)2(F4bdc)(dmso)6] b	Yb	Cl/CN	1-5 monolayers	[56]
127	XIKNUD	[Yb2(C6O4(CN)Cl)3(dmf)6]	Yb	Cl/CN	1–4 monolayers	[48]
149	POMVIZ	[Er2(C6O4(CN)Cl)3(dmso)6]	Er	Cl/CN	–	[37]

(^a) dobdc²⁻ = dianion of 2,5-dihydroxybenzene-1,4-dicarboxylic acid; (^b) the dianion of 2,3,5,6-tetrafluorobenzene-1,4-dicarboxylic acid (H₂F₄bdc).

The series [Ln₂(C₆O₄(CN)Cl)₃(dmf)₆]·G with Ln/G = Nd/2CH₂Cl₂ (53), Er/2CH₂Cl₂ (54) and Yb/- (127) has also been prepared as thin films, with a thickness of 1-4 monolayers and a few microns lateral dimensions, using the same wet sonication and drop-casting method [48]. This method has also recently been used to prepare thin films of compounds [Ln₂(C₆O₄(CN)Cl)₃(dmso)₄]·dmso, with Ln = Yb (88), Yb/Er (89) and [Er₂(C₆O₄(CN)Cl)₃(dmso)₆] (149), although the thickness of the drop-casted films was not reported [37].

Finally, there are two more Ln-anilato compounds that have been prepared as thin films: [Yb₄(C₆O₄(CN)Cl)₅(dobdc)(dmso)₁₀]·2dmso (111) and [Yb₂(C₆O₄(CN)Cl)₂(F₄bdc)(dmso)₆] (112). Nanosheets with 1-5 monolayers thickness and a few microns lateral dimensions of these compounds, prepared with the same sonication plus drop-casting method, have been very recently reported [56].

8. Conclusions

The rich coordination chemistry of anilato-type ligands when combined with Ln(III) ions, including La, Y and Lu, has produced in the last two decades around 150 different complexes and coordination polymers. In all these compounds, the anilato ligands act as bidentate or bis-bidentate, connecting two Ln(III) ions to generate monomers, dimers, tetramers, chains, layers, or 3D structures. These Ln-anilato compounds can be classified according to the dimensionality, nuclearity and topology into: (i) monomers (only two reported compounds); (ii) dimers (twenty-five reported compounds); (iii) tetramers (only one reported compound); (iv) chains (only two reported examples: a zigzag and a ladder chain); (v) regular hexagonal honeycomb layers (twenty-two prepared compounds); (vi) distorted hexagonal layers (thirty-nine prepared compounds); (vii) rectangular brick-wall type layers (seventeen known examples); (viii) rectangular herringbone type layers (fifteen reported cases); (ix) other 2D structures, including one (3,4)-gon lattice, twenty (4,4)-gon lattices and two mixed (3,4)+(3,8)-gon lattices and (x) 3D structures, including five adamantane, one 3D-noq and one 3D-4,4-c lattices.

These more than one hundred and fifty Ln-anilato compounds prepared to date include sixty-three examples with chloranilato (X = Cl), thirty-one with bromanilato (X = Br), twenty-five with the asymmetric chlorocyananilato (X = Cl and CN), nineteen with dhbq²⁻ (X = H), five with nitranilato (X = NO₂), three with methylanilato (X = CH₃), three with tert-butylanilato (X = t-Bu) and two with fluoranilato.

If we look at the Ln(III) ions combined with anilato ligands, we can see that Y(III), Dy(III) and Er(III) are the most used lanthanoids, with eighteen compounds of each. There are twelve compounds with Ce(III) and Yb(III), ten compounds with Nd(III), Eu(III) and Gd(III); eight compounds with Pr(III), Tb(III) and Ho(III); seven with La(III); and three with Tm(III) and Lu(III). That Dy(III), Er(III) and Y(III) are the most used ones to date is not casual. Y(III) was largely used in the first studies since it crystallizes very easily, whereas Dy(III) and Er(III) are being used more recently in the search of SMMs and SIMs.

The good magnetic isolation provided by the anilato ligands constitutes an advantage to obtain slow relaxation of the magnetization of the Ln(III) ions. Thus, a total of fourteen single-molecule and single-ion magnets have been prepared to date with Ln(III) and anilato ligands. These fourteen examples include one monomer, seven dimers and six 2D lattices (two hexagonal 3,6-gon, two herringbone 3,6-gon and two square 4,4-gon lattices). In most cases, these compounds behave as field-induced-SMM or SIM since the application of a DC field (usually around 1000 Oe) is needed to suppress the fast relaxation of the magnetization through a quantum tunnelling mechanism. In a few dimers, the anilato bridge has been reduced, increasing the magnetic coupling and giving rise to SMM with no DC field applied. Doping an Eu layer with 2% of Dy(III) also results in a SMM behaviour with no applied DC field. As expected, most of these SMMs and SIMs have been prepared with Dy(III) ions, although there is one example with Yb(III), one with Er(III) and even one with the isotropic Gd(III) ion.

Given the well-known luminescence on many Ln(III) compounds and the, less known, luminescence shown by some anilato ligands, in the last three years a total of seventeen Ln-anilato compounds have been reported to present luminescence either from the ligand, from the Ln(III) ion, or from both. In most cases, the emission from the ligand, centred at around 590–720 nm, coexist with the NIR emission of the Ln(III) ions (in the Yb, Er, Ho and Nd compounds). Interestingly, the luminescence is essentially maintained (although with slight shifts in the emission bands) when the compounds are delaminated and prepared as drop-casted thin films.

Also, recently, some of these layered coordination polymers have shown a remarkable capacity to release the solvent molecules (usually water) located between the layers by gentle heating or under vacuum at room temperature. This dehydration results in a collapse of the crystal structure that can be easily fully recovered by immersing the dehydrated compounds in water. Furthermore, besides this reversible water release/uptake, some dehydrated compounds also show the capacity to adsorb other solvents, keeping the original structure or giving rise to novel crystal structures. Interestingly, the dehydrated compounds can also adsorb gas molecules such as H₂, N₂, CH₄ and CO₂.

A very recent study has also shown a remarkable solvent exchange capacity in three layered compounds without the need to previously evacuate the original solvent molecules. This result opens the way to the synthesis of different solvates starting from one on them.

The capacity of the anilato ligands to be reduced to the corresponding semiquinone and cathecolato forms has also been checked in some Ln-anilato dimers, electrochemically and chemically, resulting in an increase of the magnetic coupling between the Ln(III) ions and in the observation of slow relaxation of the magnetization even with zero applied DC field.

Last, but not least, these layered materials can be easily delaminated and drop-casted in thin films with a few monolayers thickness and micrometric lateral dimensions. Interestingly, the optical properties are retained in these thin films.

The future directions of these Ln-anilato based materials are many and very promising. Thus, the great variety of structures will soon increase with the synthesis of novel compounds with other coordinating solvents and coligands, specially, with bridging ones. Furthermore, some very recent results have shown the possibility to modulate, at will, the dimensionality of these, in some cases, porous materials. This capacity may lead to the synthesis of 2D and 3D structures with predetermined porous sizes and dimensionalities. The use of different X groups in the anilato rings will allow a modulation not only of the size but also the nucleophilicity and hydrophilicity of the cavities, channels and interlaminar spaces created in these structures. The use of different templating cations in the anionic Ln-anilato lattices, constitute another very interesting tool to control the dimensionality and properties of these materials.

Besides the structural aspects, the magnetic properties of these materials constitute a second interesting aspect worth to investigate. The use of different very asymmetric coligands may lead to an increase in the anisotropy of the Ln(III) coordination geometry that may result in an increase in the energy barriers and blocking temperatures of these SMMs and SIMs.

The luminescence displayed by many Ln(III) ions and their sensitivity to changes in their coordination environments is another important aspect to exploit and develop. Furthermore, given the gas absorption capacity and solvent or ligand exchange ability shown by some of these materials, they are promising candidates to prepare devices with sensing capacity towards different gas, solvent and ionic species. The capacity to be delaminated into large thin films with a few nanometers thickness represents an additional advantage for this purpose.

Finally, the redox activity of the anilato ligand adds additional potentialities to these materials since the reduced materials might be good electronic conductors or semiconductors (specially, if combined with Ce(III), Eu(III) or Yb(III) that have two accessible oxidation states) [70] and may also show promising magnetic properties as already shown by some Ln(III)-anilato-Ln(III) dimers with reduced anilato bridges. Finally, they may also find applications as redox/luminescent sensors since their electronic and optical properties change dramatically upon reduction of the anilato ligands.

In summary, all the above-mentioned properties in these Ln-anilato compounds render them as good candidates to prepare devices with potential applications.

CCDC-1944109-14, 1944117, 1944118, 1944120, 1944123, 1944124, 1565271-80, 1944126, 1944127 and 1565282 contain the crystallographic data for compounds 43-48, 49, 67, 68, 69, 70, 72-81, 99, 100 and 102, respectively. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre at www.ccdc.cam.ac.uk/data_request/cif.