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Article

Cobalt and Iron Cyano Benzene Bis(Dithiolene) Complexes

by
António G. Costa
1,
Gonçalo Lopes
1,
João F. G. Rodrigues
1,
Isabel C. Santos
1,
Dulce Simão
2,
Elsa B. Lopes
1,
Laura C. J. Pereira
1,
Nolwenn Le Breton
3,
Sylvie Choua
3,
Stéphane A. Baudron
4,
Manuel Almeida
1 and
Sandra Rabaça
1,*
1
Centro de Ciências e Tecnologias Nucleares (C2TN), Associação do Instituto Superior Técnico para a Investigação e Desenvolvimento (IST-ID), Departamento de Engenharia e Tecnologias Nucleares (DECN), Instituto Superior Técnico (IST), Universidade de Lisboa, Estrada Nacional 10, 2695-066 Bobadela, Portugal
2
Centro de Química Estrutural (CQE), Associação do Instituto Superior Técnico para a Investigação e Desenvolvimento (IST-ID), Departamento de Engenharia Química (DEQ), Instituto Superior Técnico (IST), Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
3
Institut de Chimie, UMR CNRS 7177, Université de Strasbourg, Institut Le Bel, 4 Rue Blaise Pascal, CS 90032, 67081 Strasbourg, France
4
CNRS, CMC UMR 7140, Université de Strasbourg, 4 rue Blaise Pascal, 67000 Strasbourg, France
*
Author to whom correspondence should be addressed.
Crystals 2024, 14(5), 469; https://doi.org/10.3390/cryst14050469
Submission received: 16 April 2024 / Revised: 7 May 2024 / Accepted: 14 May 2024 / Published: 17 May 2024
(This article belongs to the Section Inorganic Crystalline Materials)
Browse Figures
Versions Notes

Abstract

:
New iron and cobalt bis(dithiolene) complexes [M(3cbdt)2] (3cbdt = 3-cyanobenzene-1,2-dithiolate) were prepared as tetraphenylphosphonium (Ph4P+) salts for Fe in the monoanionic state and for Co in both the dianionic and monoanionic states: (Ph4P)2[Fe(III)(3cbdt)2]2 (1); (Ph4P)2[Co(III)(3cbdt)2]2 (2); (Ph4P)2[Co(II)(3cbdt)2] (3). These compounds were characterized by single-crystal X-ray diffraction, cyclic voltammetry, EPR, and static magnetic susceptibility. Their properties are discussed in comparison with the corresponding complexes based on the isomer ligand 4-cyanobenzene-1,2-dithiolate (4cbdt) and 4,5-cyanobenzene-1,2-dithiolate (dcbdt), previously described by us. The Fe(III) and the Co(III) compounds (1 and 2) are isostructural, crystallizing in the triclinic P 1 ¯ space group, with cis [M(III)(3cbdt)2] complexes dimerized in a trans fashion, and the transition metal (M = Fe, Co) has a distorted 4+1 square pyramidal coordination geometry. The Co(II) compound (3) crystallizes in the triclinic P 1 ¯ space group, with the unit cell containing one cis and three trans inequivalent [Co(II)(3cbdt)2] complexes with the transition metal (Co) and having a square planar coordination geometry. The Fe(III) complex (1) is EPR-silent, and the static magnetic susceptibility shows a temperature dependence typical of dimers of antiferromagnetically coupled S = 3/2 spins with −J/kB = 233.6 K and g = 1.8. Static magnetic susceptibility measurements of compound (3) show that this Co(II) complex is paramagnetic, corresponding to an S = ½ state with g = 2, in agreement with EPR spectra showing in solid state a hyperfine structure typical of the I(59Co) = 7/2. Static susceptibility measurements of Co(III) complex (2) showed an increase in the paramagnetic susceptibility upon warming above 100 K, which is consistent with strong AFM coupling between dimerized S = 1 units with a constant −J/kB ~1286 K.

1. Introduction

Transition-metal dithiolene complexes have been attracting continuous attention for more than 50 years [1,2,3,4,5], becoming a large class of compounds increasingly relevant both for fundamental studies in coordination chemistry and in different fields and applications from materials science [6,7], catalysis [8], bioinorganic chemistry [9,10,11], energy conversion [12,13,14] and biological systems [15]. In spite of a quite long and extensive research history, these compounds continue to be studied, with novel families being frequently identified and providing revitalizing sources of interest [16].
A key feature of the bis(dithiolene) complexes is their capability to assume different oxidation states. The vivid redox behavior of many of these complexes is due to a significant contribution of the ligands to the frontier orbitals, playing the so-called non-innocent role in ligand-centered redox processes [17,18,19]. The possibility to obtain complexes in different oxidation states and with different metals provides access to different magnetic moments constituting useful degrees of freedom in the design of the magnetic properties of molecular materials.
As a general tendency, the monoanionic state is the most stable within bis(dithiolene) complexes. Dianionic states are also frequently obtained and, in some cases, are neutral complexes, or in even higher oxidation states, they can be isolated in stable compounds. Furthermore, the electroactive character of these complexes frequently permits the existence of persistent partially oxidized states. Recent developments have spotlighted instances where these complexes, while in their neutral state, manifest remarkable electrical conductivity and authentic metallic characteristics [18,19,20].
The d-metal dithiolene complexes also present a very rich structural diversity. Most studies have been focused on transition metals such as Au, Ni, Pd, Pt, Cu, Ag, or Zn, and among about 2568 entries in the CCDC database, the square planar coordination geometry is dominant, and only 169 entries refer to Co and Fe. For Fe, a dimeric arrangement of Fe bis(dithiolene) monoanionic units with a (4+1) square pyramidal coordination is the prevailing norm, with only two exceptional cases: (n-Bu4N) [Fe(qdt)2] (qdt = 2,3-quinoxalinedithiolate) [21] and [Fe(S2C2(p-anisyl)2)2] [22], where this dimerization could be prevented due to specific solid-state interactions and a square planar geometry being observed.
For Co, a larger structural diversity has been observed, with the dimerization being less favored. In addition to the square planar geometry, bis(dithiolene) complexes are known to adopt also dimeric [23,24], trimeric [25], and even polymeric [26] arrangements due to the formation of extra apical Co over S bonds.
Previously, we focused our attention on transition-metal bis(dithiolene) complexes with cyano benzene ligands and reported extensive studies of two families of complexes: [M(dcbdt)2] [24,27,28,29,30,31,32] and [M(4cbdt)2] [33,34], with different d-metals M = Zn, Ni, Pd, Pt, Co, Cu, Fe, Au). Here, dcbdt (dicyanobenzene-1,2-dithiolate) and 4cbdt (4-cyanobenzene-1,2-dithiolate) were employed as ligands (Figure 1). The incorporation of cyano groups into dithiolene ligands is regarded as an interesting tool for tailoring the physical properties of these complexes. The number and position of electron-withdrawing groups (–C≡N) on both the dithiolene complexes as well as in the analogous TTF donors [35,36,37] are known to considerably influence their redox characteristics. In addition, these cyano moieties offer secondary coordination possibilities for constructing more complex heterometallic coordination architectures and networks [38,39,40,41,42,43,44,45] and may also provide –C≡N…H interactions, promoting distinctive structural motifs in the solid state.
More recently, we reported the nickel and copper complexes [M(3cbdt)2]Z− (Z = 1, 2 and M = Ni, Cu) [46] as the first two members of a new family of bis(dithiolene) complexes with a new isomer of the cyano benzene dithiolene ligand, 3-cyanobenzene-1,2-dithiolate. In this work, we report the iron and cobalt complexes with this ligand, [Fe(3cbdt)2] and [Co(3cbdt)2], which were obtained as tetraphenylphosphonium salts for Fe in the monoanionic state and for Co in both the dianionic and monoanionic states, with the last one being isostructural to the Fe analog. The monoanionic complexes present dimerization with a distorted square pyramidal 4 + 1 metal coordination geometry.

2. Materials and Methods

2.1. General Information

The 2-oxobenzo[d][1,3]dithiole-4-carbonitrile [37] was synthesized following previously published procedures, and all the other reagents were purchased from commercial sources and used without any additional purification.

2.2. Synthesis

(Ph4P)2[Fe(3cbdt)2]2. 2CH2Cl2 (1). Initially, 2-oxobenzo[d][1,3]dithiole-4-carbonitrile (100 mg, 0.52 mmol) was dissolved in a NaOH solution (100 mg, 2.5 mmol) in 10 mL of H2O/EtOH (1:1) using a water bath at 50 °C. Within 10 min of stirring, the solution turned clear yellow. Subsequently, a solution of FeCl3 (46 mg, 0.267 mmol) in 5 mL of H2O/EtOH (1:1) was added. After stirring for 5 min, a solution of Ph4PBr (250 mg, 0.59 mmol) in 10 mL of H2O/EtOH (1:1) was introduced. The solution was then left overnight at low temperatures (between 0 °C and 7 °C). The resulting brown precipitate was filtered, washed with cold methanol, and dried. Finally, the compound was recrystallized in CH2Cl2/hexane, yielding black crystals after 1 week. (103 mg, 0.072 mmol, 55.38%). M.p. 300 °C; FTIR (cm−1): ν = 3050 (w, Ar–H), 2212 (s, C≡N), 1550–1482 (m, C=C); ESI-MS: (+) obs. m/z 339.2, calcd. m/z 339.130 ((Ph4P)+, 100%); (−) obs. m/z 771.8, calcd. m/z 771.75 ([Fe(3cbdt)2]22−, 100%); Anal. calcd for C78H56Cl4Fe2N4P2S8(1621.28): C 57.78, H 3.48, N 3.46, S 15.82. Found: C 58.12, H 3.57, N 3.68, S 16.12.
(Ph4P)2[Co(3cbdt)2]2. 2CH2Cl2 (2). Following a similar procedure as used for 1 but with a solution of CoCl2.6H2O (64 mg, 0.26 mmol) instead of FeCl3, 2 was obtained as black needles (95 mg, 0.069 mmol, 53.07%). M.p. 201–203 °C; FTIR (cm−1): ν = 3057 (w, Ar–H), 2210 (s, C≡N), 1560–1492 (m, C=C); ESI-MS: (+) obs. m/z 339.2, calcd. m/z 339.130 ((Ph4P)+, 100%); (−) obs. m/z 777.7, calcd. m/z 777.75 ([Co(3cbdt)2]22−, 100%); Anal. calcd for C78H56Cl4Co2N4P2S8 (1627.45): C 57.56, H 3.47, N 3.44, S 15.76. Found: C 57.82, H 3.10, N 3.49, S 16.20.
(Ph4P)2[Co(3cbdt)2] (3). Under a nitrogen atmosphere, 2-oxobenzo[d][1,3]dithiole-4-carbonitrile (100 mg, 0.52 mmol) was dissolved in a MeONa solution (90 mg, 1.6 mmol) in 2 mL of MeOH. The solution turned clear yellow within 5 min of stirring. Subsequently, a solution of CoCl2·6H2O (64 mg, 0.26 mmol) in 2 mL of MeOH was prepared and added to the previous solution. After stirring for 5 min, a Ph4PBr (0.22 mg, 0.52 mmol) solution in 2 mL of the same solvent was added to this mixture. The solution was left to stand for 2 days at low temperatures (between 0 °C and 7 °C), resulting in the formation of needle-shaped blue crystals (80 mg, 0.075 mmol, 28.9% yield). M.p. 170–171 °C; FTIR (cm−1): ν = 3042 (w, Ar–H), 2213 (s, C≡N), 1583–1482 (m, C=C); ESI-MS: (+) obs. m/z 339.2, calcd. m/z 339.130 ((Ph4P)+, 100%); (−) obs. m/z 388.7, calcd. m/z 388.87 ([Co(3cbdt)2]−, 100%); Anal. calcd for C62H46CoN2P2S4 (1068.18): C 69.71, H 4.34, N 2.62, S 12.01 Found: C 70.10, H 4.23, N 2.75, S 12.41.

2.3. X-ray Crystallography

Crystals of 1–3 were prepared for analysis by mounting them on a cryoloop immersed in FOMBLIM protective oil. Data collection was performed using a Bruker D8 QUEST diffractometer equipped with graphite-monochromated Mo Kα radiation (α = 0.71073 Å) in φ and ω scan modes, with data acquisition managed by the APEX3 program [47]. The unit cell parameters were determined using Bruker SMART software (Version 6.45) and refined using the Bruker SAINT program applied to all observed reflections [48]. Empirical absorption corrections were applied using SADABS [49]. Structure solutions were achieved through direct methods utilizing SHELXT [50], followed by full-matrix least-squares refinement against F2 using SHELXL [51], which is integrated into the WINGX program package [52]. Most non-hydrogen atoms were refined with anisotropic thermal parameters, while hydrogen atoms were positioned at idealized locations and allowed to refine in relation to their parent carbon atoms. Molecular visualizations were generated using Mercury [53]. The supplementary crystallographic data for this paper can be accessed via the Cambridge Crystallographic Data Centre (CCDC) deposition numbers 2346079, 23406080, and 23406081, available for free download at www.ccdc.cam.ac.uk/data_request/cif, accessed on 16 April 2024. Crystallographic data for compounds 1–3 are summarized in Table 1.

2.4. Cyclic Voltammetry Studies

Cyclic voltammetry data were obtained using a BAS C3 Cell Stand. The voltammograms were obtained at room temperature with variable scan rates in the range of 50–500 mV s−1, using platinum wire working, counter electrodes, and an Ag/AgNO3 (0.01 M AgNO3 and 0.1 M nBu4NPF6 in acetonitrile) reference electrode, in which the Ag+ ion electrode was separated from the bulk solution by a Vycor™ frit. The measurements were performed on fresh solutions with a concentration of ~0.5 × 10−3 M in acetonitrile, which contained n-Bu4NPF6 (0.1 M) as a supporting electrolyte. Ferrocene was added directly to the solution after cyclic voltammogram registration to allow for the potential normalization in situ, relative to the ferrocene/ferrocenium couple redox potential that was found to be at E1/2 = 0.36 V vs. Ag/AgNO3.

2.5. Magnetic Susceptibility Measurements

Magnetic susceptibility measurements were conducted on polycrystalline samples weighing approximately 10–15 mg each. These measurements were performed using a 7 Tesla S700X SQUID magnetometer manufactured by Cryogenic Ltd., (London, UK) over a temperature range of 4 to 300 K, and with an applied magnetic field of 1 T. Paramagnetic susceptibility values were derived from the raw data and adjusted for sample holder contributions, incorporating a diamagnetic correction based on tabulated Pascal constants, yielding values of −832 × 10−6 emu/mol, −832 × 10−6 emu/mol and −665 × 10−6 emu/mol for (Ph4P)2[Fe(3cbdt)2]2, (Ph4P)2[Co(3cbdt)2]2 and (Ph4P)2[Co(3cbdt)2], respectively.

2.6. EPR Spectrometry

EPR spectra were recorded on an EMX spectrometer (Bruker Biospin GmbH, Ettlingen, Germany) operating at X-band, equipped with a high sensitivity resonator (ER4119HS, Bruker, Ettlingen, Germany) and a variable temperature unit (ER4131VT, Bruker). Spectra were simulated using Easyspin 6.0.0-dev.54.

2.7. Mass Spectrometry

Mass spectra were obtained by electrospray ionization (ESI-MS) in a Bruker HCT quadrupole ion trap mass spectrometer (Bruker Daltonics GmbH, Bremen, Germany).

3. Results

3.1. Tetraphenylphosphonium Bis(Dithiolene) Complexes Synthesis

The [Fe(3cbdt)2]− and [Co(3cbdt)2]2−/− complexes were obtained as tetraphenylphosphonium salts, from the proligand 2-oxobenzo[d][1,3]dithiole-4-carbonitrile (A) prepared as previously described [37], following procedures similar to those recently described for preparing the Ni and Cu complexes. [46] The benzothioxo A was reacted in a basic medium with chloride salts of cobalt or iron, and the resulting metal bis(dithiolene) complexes precipitated as tetraphenylphosphonium salts upon the addition of (Ph4P)Br (Figure 2).
Under anaerobic conditions in methanol solutions, the dianionic Co complex (Ph4P)2[Co(3cbdt)2] (3) was obtained as needle-shaped orange crystals. Under open atmospheric conditions and in ethanol/water solutions, the monoanionic Fe and Co complexes (Ph4P)2[M(3cbdt)2]2 (M = Fe (1), Co (2)) were obtained. The dianionic Co complex was found to be not stable in solution under open atmospheric conditions and readily oxidizes, with the monoanionic Co complex being obtained upon the recrystallization of the dianionic complex under atmospheric conditions.

3.2. Electrochemical Properties

The redox properties of the Fe and Co complexes were investigated by cyclic voltammetry in acetonitrile and starting from the monoanionic complexes, (Ph4P)2[M(3cbdt)2]2 (M = Fe, Co).
A quasi-reversible redox process ascribed to the couple [M(3cbdt)2]2−/[M(3cbdt)2]− is observed at −1.08 and −0.826 V (versus Ag/AgNO3) for M = Fe and Co respectively (see Figure S1. These potentials are almost comparable to those observed for the analogs with the ligand 4cbdt and as expected more negative than those observed for the dicyano-substituted ligand dcbdt as shown in Table S1. For the Fe compound, between −0.5 and 0.6 V, we observed an intricate redox process with multiple-step reduction and oxidation waves that may be due to the redox processes involving dimerized and undimerized species in equilibrium, with the dimer dissociation degree being strongly dependent on the nature of the solvent, as previously described for other Fe bis(dithiolene) complexes [54].

3.3. Crystal and Molecular Structures of the [M(3cbdt)2]22− M = Fe, Co Complexes

Crystals of 1 and 2 suitable for X-ray diffraction were obtained after recrystallization from CH2Cl2/Hexane. These compounds are isostructural and ORTEP views of the complexes, are depicted in Figure 3a,b. Selected bond lengths and angles for these compounds are presented in Tables S2 and S3.
The asymmetric unit of 1 and 2 contains one Ph4P+ cation, one [M(3cbdt)2]− (M = Fe, Co) anion with the CN groups in the cis configuration, and one dichloromethane solvent molecule. The anions present the characteristic dimerization of Fe(III) and Co(III) bis(dithiolenes) forming [M(3cbdt)2]22− (M = Fe, Co) dimer units with an inversion center between the two metal atoms, which adopt a 4+1 coordination geometry with a metal-over- sulfur overlap mode.
For five-coordinate species, the angular geometric parameter (τ5) can be defined by the equation τ5 = (β − α)/60° (where β = the largest angle, α = the second-largest angle around the central atom) [55,56]. In an idealized scenario, this value should be one for trigonal bipyramidal geometry and zero for square pyramidal geometry. Compound 1 exhibits angles around the Fe central atom, with values of 169.96° for the largest angle (β) and 152.30° for the second-largest angle (α). Compound 2 exhibits angles around the Co central atom, with values of 177.18° for the largest angle (β) and 155.441° for the second-largest angle (α). By applying the above concept, the coordination geometry around the Fe center (τ5 = 0.29) and around Co center (τ5 = 0.36) can be more accurately described as distorted square pyramidal rather than trigonal bipyramidal.
The ligands are slightly distorted, repelling each other and making the distance between their mean planes larger than the central M-S distance. The equatorial M–S bond distances (Fe–S1 2.219(2) Å, Fe–S2 2.215(3) Å, Fe–S3 2.217(2) Å, Fe–S4 2.221(2) Å, and Co–S1 2.203(1) Å, Co–S2 2.180(2) Å, Co–S3 2.203(2) Å, Co–S4 2.188(2) Å) and the Fe–S4, Co–S4, apical bonds at 2.461(2) Å, 2.351(1) Å are typical of Fe(III) and Co(III) dimerized complexes, respectively [30,32,33]. The bond lengths of the ligand, namely the S-C and C-C values, are identical to those observed in other similar complexes within the experimental error.
As shown in Figure 4, the crystal structure of these compounds is made up of dimeric anion layers intercalating with cation layers, allowing for anion–anion short C≡N…H–C contacts C(4)–H(4)…N(2)≡C(14) in both structures—at 2.500 Å and 2.542 Å, for 1 and 2, respectively—and several other anion–anion interactions slightly longer than the sum of the van der Waals radius (Figure 5).
Crystals of 3 suitable for X-ray diffraction were obtained directly from the synthesis and ORTEP view of the complexes, as depicted in Figure 3c. Selected bond lengths and angles for these compounds are presented in Table S4.
The asymmetric unit of 3 contains six Ph4P+ cations, one [Co(3cbdt)2]2− dianion with the CN groups in the cis configuration, another [Co(3cbdt)2]2− dianion with the CN groups in the trans configuration, and two halves of [Co(3cbdt)2]2− dianions. In this structure, the dianions present the usual square planar coordination geometry; they are essentially planar with the bond lengths and angles within the expected range for other dianionic bis(dithiolate) Co(II) complexes. The crystal structure is such that the dianions are completely surrounded by cations and there are no short anion–anion contacts. The crystal structure can be described as two mixed anion cation layers (Layer I and Layer II) alternating along the c axis (Figure 6).
All the compounds were insulators. The electrical conductivity was measured only at room temperature (see Supplementary Materials).

3.4. Magnetic Properties of the [M(3cbdt)2]22− M = Fe, Co Complexes

The magnetic properties of these compounds were investigated by EPR spectrometry and static magnetic susceptibility measurements in the temperature range 4–300 K.
Concerning monoanionic Co(III) bis(dithiolene) complexes containing a d6 species, both low-spin S = 0 and high-spin S = 1 states have been reported depending on the ligand. While most of them are diamagnetic, high-spin states have been described for complexes with some ligands, e.g., substituted benzodithiolates [23,24,57,58,59].
The Fe(III) complex with a d5 species is expected to be paramagnetic either in low-spin S = 1/2, intermediate-spin S = 3/2 or high-spin S = 5/2 states. However, upon dimerization, as observed in 1 and 2, a significant antiferromagnetic interaction between units of the dimer is expected to lead to a diamagnetic ground state, which dominates low-temperature susceptibility, and with excited multiplet states, being thermally accessible can lead to an increasing paramagnetism at higher temperatures.
The iron complex 1 was found to be EPR-silent both at room temperature and 100 K, as was the case with most of the dimerized Fe(III) bis(dithiolene) complexes. However, the magnetic susceptibility measurements show a paramagnetic behavior, with a room temperature susceptibility of 3.8 × 10−3 emu/mol decreasing upon cooling towards a minimum at ~28 K ~1.2 × 10−3 emu/mol. This was followed by a low temperature increase (Figure 7), which can be ascribed to a Curie tail due to paramagnetic impurities or defects. This behavior is typical of a system of antiferromagnetically coupled dimers with a diamagnetic ground state. The paramagnetic susceptibility data for 1 were fitted considering models of both S = 1/2 and S = 3/2 dimerized species. The best fit was obtained for S = 3/2 using the equation:
χ P = A + C T + 2 N g 2 μ B 2 k T e J k T + 5 e 3 J k T + 14 e 6 J k T 1 + 3 e J k T + 5 e 3 J k T + 7 e 6 J k T
with an antiferromagnetic coupling constant −J/kB = 233.6 K, g = 1.8, a temperature independent contribution A = 9.95 × 10−4 emu/mol, and C = 0.013 emu K/mol, which corresponds to approximately 0.7% of S = 3/2 impurities. These parameters are identical to those reported for other dimerized Fe(III) bis(dithiolene) complexes where the S = 3/2 model has been found in most cases as the most appropriated [33,60,61].
The dianionic Co(II) complex, (Ph4P)2[Co(3cbdt)2] (3), as expected for a d7 species, was found to be paramagnetic with an almost temperature-independent effective magnetic moment of µeff ~2 μB above 25 K (Figure 8). This value is close to the one expected for a spin-only value S = 1/2 system, with g = 2.0 (µS = 1.73 μB and µeff = 1.8 μB considering spin-orbit coupling usually found in Co complexes), which is identical to those reported for other Co(II) bis(dithiolene) complexes such as [Co(dcbdt)2]2− [24].
The paramagnetic nature of 3 was confirmed by EPR spectrometry, showing (Figure 9) a rhombic system with eight lines partially resolved in the gz region due to the interaction with the 59Co nuclear spin I = 7/2 [62,63,64]. This hyperfine structure is usually observed only in diluted systems when there is a large separation between the complexes reducing the effects of dipolar interactions, and this is a rare example of such a situation for a pure compound in the solid state due to the large separation between the Co complexes by the cations, with the smallest Co-Co distance being 10.794 Å. The simulation of the spectra was conducted with the following parameters: gxx = 1.938, gyy = 2.098, gzz = 3.036, Axx(59Co) = 10 MHz, Ayy(59Co) = 190, MHz, Azz(59Co) = 356 MHz, (linewidth using gstrainxx = 0.12, gstrainyy = 0.10 and gstrainzz = 0.14). The observed spectrum is quite similar to those observed in the salts of [Co(cbdt)2]2− and [Co(dcbdt)2]2−, where the hyperfine interaction was found to be around 300 MHz [24,34,65].
The Co(III) dimerized compound (Ph4P)2[Co(3cbdt)2]2 (2) was found to be EPR-silent at room temperature and at 100 K. A possible high-spin state for the Co(III) is denoted by the static magnetic susceptibility measurements (Figure 10), which in addition to a low-temperature Curie tail, show a modest but significant increase in paramagnetic susceptibility above 100 K, which can be ascribed to the multiplet states becoming increasingly thermally accessible from the singlet ground state. However, this modest increase in susceptibility is indicative of dimer antiferromagnetic coupling J significantly larger than room temperature. A good fit of the dimer equation below, which describes the susceptibility for dinuclear homospin system with S = 1 (singlet-quintet model), was obtained with J/kB ≈ −1286 K.
χ p = A + C T + 2 N g 2 μ B 2 k T exp ⁡ J k T + 5 ( exp ⁡ 3 J k T ) 1 + 3 exp ⁡ J k T + 5 e x p ( 3 J k T )

4. Conclusions

In this work, we reported three new compounds: two bis(dithiolene) complexes obtained in the monoanionic state—[M(3cbdt)2]− with M = Fe and Co—and one bis(dithiolene) complex obtained in the dianionic state: [M(3cbdt)2]2− with M = Co. The monoanionic complexes of Co and Fe both exhibit typical dimerization, featuring a 4 + 1 metal coordination geometry ([M(3cbdt)2]22− (M = Fe and Co)). The coordination geometry around the Fe center (τ5 = 0.29) and the Co center (τ5 = 0.36) is distorted and square pyramidal. The dimerized monoanionic Co(III) complex ([Co(3cbdt)2]22−) is EPR-silent and is an example of a cobalt complex with a high-spin S = 1 ground state. The Co(II) dianionic complex (Co(3cbdt)2]2−) is a paramagnetic S = ½ system and a rare example showing, in the solid-state EPR, the hyperfine structure of the I(59Co) = 7/2. The dimerized monoanionic Fe(III) complex ([Fe(3cbdt)2]22−) was found to be EPR-silent, as was the case with most of the dimerized Fe(III) bis(dithiolene) complexes. The magnetic susceptibility measurements show a paramagnetic behavior typical of antiferromagnetically coupled S = 3/2 species with a coupling constant of −J/kB = 233.6 K.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/cryst14050469/s1, Figure S1: Cyclic voltammograms of [Ph4P][Fe(3cbdt)2] (top) and [Ph4P][Co(3cbdt)2] (bottom) in CH3CN with [n-Bu4N][PF6] 0.1 M as electrolyte, V vs. Ag/Ag+, scan rate 100 mV s−1.; Table S1: Redox potentials of [M(L)2]2−/[M(L)2]−, M=Co, Fe; L=3-cbdt and 4-cbdt in acetonitrile (ref. Ag/AgNO3); Table S2: Bond lengths [Å] and angles [deg] for compound 1; Table S3: Bond lengths [Å] and angles [deg] for compound 2; Table S4: Bond lengths [Å] and angles [deg] for compound 3; electrical transport measurements.

Author Contributions

S.R. was responsible for the original conceptualization of this work. The manuscript was prepared based on research contributions from all the authors in different topics, namely A.G.C., G.L., J.F.G.R. and D.S. concerning sample preparation, I.C.S. and A.G.C. the structural analysis, E.B.L. the electrical transport measurements, L.C.J.P. and A.G.C. the magnetic characterization discussion and final review, N.L.B. and S.C. the EPR measurements and discussion. S.R., S.A.B. and M.A. ensured funding acquisition and the final review and editing of the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by Fundação para a Ciência e a Tecnologia (FCT) through UID/Multi/04349/2019, the National Infrastructure Roadmap, LTHMFL-NECL LISBOA-01-0145-FEDER-022096, RNEM—Portuguese Mass Spectrometry Network, LISBOA-01-0145-FEDER-022125, also funded by the Lisboa Regional Operational Program (Lisboa2020) under the PT2020 Partnership Agreement, via the European Regional Development Fund (ERDF). The collaboration between the Portuguese and French team members was supported by the “PHC PESSOA” programme (project number: 47836RH), funded by the French Ministry for Europe and Foreign Affairs, the French Ministry for Higher Education and Research and the Portuguese FCT.

Data Availability Statement

The data supporting the conclusions of this article will be made available by the authors on request.

Acknowledgments

Financial support from the CNRS and the University of Strasbourg is gratefully acknowledged.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Molecular scheme of the cyano benzene bis(dithiolene) metal complexes [M(3cbdt)2], [M(4cbdt)2] and [M(dcbdt)2].
Figure 1. Molecular scheme of the cyano benzene bis(dithiolene) metal complexes [M(3cbdt)2], [M(4cbdt)2] and [M(dcbdt)2].
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Figure 2. Synthetic route to bis(dithiolene) complexes [M(3cbdt)2] M = Fe and Co. Reaction conditions: proligand (A) cleavage (i); metallic salt for the complexation (ii); cation salt for bis(dithiolate) complex precipitation (iii).
Figure 2. Synthetic route to bis(dithiolene) complexes [M(3cbdt)2] M = Fe and Co. Reaction conditions: proligand (A) cleavage (i); metallic salt for the complexation (ii); cation salt for bis(dithiolate) complex precipitation (iii).
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Crystals 14 00469 g003
Figure 3. Metal bis(dithiolate) complexes ORTEP diagrams: (Ph4P)2[Fe(3cbdt)2]2 (1) (a), (Ph4P)2Co(3cbdt)2]2 (2) (b) and (Ph4P)2[Co(3cbdt)2] (3) (c). The thermal ellipsoids are drawn at 50% probability and the cations were omitted for clarity.
Figure 3. Metal bis(dithiolate) complexes ORTEP diagrams: (Ph4P)2[Fe(3cbdt)2]2 (1) (a), (Ph4P)2Co(3cbdt)2]2 (2) (b) and (Ph4P)2[Co(3cbdt)2] (3) (c). The thermal ellipsoids are drawn at 50% probability and the cations were omitted for clarity.
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Figure 4. View of a crystal structure of (Ph4P)2[Fe(3cbdt)2]2 (1) along the a axis (a) and the c axis (b).
Figure 4. View of a crystal structure of (Ph4P)2[Fe(3cbdt)2]2 (1) along the a axis (a) and the c axis (b).
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Crystals 14 00469 g005
Figure 5. Detail of the anion–anion interactions in compounds (Ph4P)2[Fe(3cbdt)2]2 2CH2Cl2 (1) (left) and (Ph4P)2[Co(3cbdt)2]2 2CH2Cl2 (2) (right).
Figure 5. Detail of the anion–anion interactions in compounds (Ph4P)2[Fe(3cbdt)2]2 2CH2Cl2 (1) (left) and (Ph4P)2[Co(3cbdt)2]2 2CH2Cl2 (2) (right).
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Figure 6. (a) Partial view of the crystal structure of (Ph4P)2[Co(3cbdt)2] (3), the cations are represented in light wireframe and anions in space fill mode are arranged in two type of layers as shown in (b). The color codes correspond to the symmetrically distinct units.
Figure 6. (a) Partial view of the crystal structure of (Ph4P)2[Co(3cbdt)2] (3), the cations are represented in light wireframe and anions in space fill mode are arranged in two type of layers as shown in (b). The color codes correspond to the symmetrically distinct units.
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Figure 7. Paramagnetic susceptibility χ of (Ph4P)2[Fe(3cbdt)2]2 (1) as a function of the temperature T. The dashed line is a fit by Equation (1), considering dimers of S = 3/2 spins (see text).
Figure 7. Paramagnetic susceptibility χ of (Ph4P)2[Fe(3cbdt)2]2 (1) as a function of the temperature T. The dashed line is a fit by Equation (1), considering dimers of S = 3/2 spins (see text).
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Figure 8. Effective magnetic moment μeff of (Ph4P)2[Co(3cbdt)2] (3), as a function of the temperature T.
Figure 8. Effective magnetic moment μeff of (Ph4P)2[Co(3cbdt)2] (3), as a function of the temperature T.
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Crystals 14 00469 g009
Figure 9. Experimental (black) and simulated (red) EPR spectra of (Ph4P)2[Co(3cbdt)2] (3) as a polycrystalline sample at room temperature. Experimental conditions: 9.3155 GHz, power of 4.9 mW and a modulation of 0.4 mT. Simulation parameters are given in the text.
Figure 9. Experimental (black) and simulated (red) EPR spectra of (Ph4P)2[Co(3cbdt)2] (3) as a polycrystalline sample at room temperature. Experimental conditions: 9.3155 GHz, power of 4.9 mW and a modulation of 0.4 mT. Simulation parameters are given in the text.
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Crystals 14 00469 g010
Figure 10. Temperature dependence of the paramagnetic susceptibility of (Ph4P)2[Co(3cbdt)2]2, (2).
Figure 10. Temperature dependence of the paramagnetic susceptibility of (Ph4P)2[Co(3cbdt)2]2, (2).
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Table 1. Crystallographic data for compounds 1–3.
Table 1. Crystallographic data for compounds 1–3.
Compound(Ph4P)2 [Fe(3cbdt)2]2 2CH2Cl2 (1)(Ph4P)2 [Co(3cbdt)2]2 2CH2Cl2 (2)(Ph4P)2[Co(3cbdt)2]
(3)
Empirical formulaC78 H56 Cl4 Fe2 N4 P2 S8C78 H56 Cl4 Co2 N4 P2 S8C62 H46 Co N2 P2 S4
Crystal size (mm)0.180 × 0.100 × 0.0400.450 × 0.180 × 0.0400.400 × 0.020 × 0.020
Molecular mass (g/mol)1621.181627.341068.12
Temperature (K)150 (2)273 (2)294 (2)
Crystal systemTriclinicTriclinicTriclinic
Space group P 1 ¯ P 1 ¯ P 1 ¯
a (Å)11.2179 (9)11.2465 (6)14.0437 (7)
b (Å)13.6086 (10)13.6794 (7)22.4513 (13)
c (Å)13.6118 (10)13.7567 (7)26.2961 (15)
α (°)108.102 (3)108.146 (2)88.930 (2)
β (°)103.708 (3)100.930 (2)78.425 (2)
γ (°)100.865 (3)103.540 (2)87.578 (2)
V (Å3)1839.9 (2)1874.65 (17)8114.8 (8)
Z, Dcalcd (Mg/m3)1, 1.4631, 1.4416, 1.311
μ (mm−1)0.8580.8970.572
F(000)8308323318
θ Range (°)2.644 to 25.6801.943 to 27.1642.910 to 25.682
Index range (h,k,l)−8 ≤ h ≤ 13, −16 ≤ k ≤ 15, −16 ≤ l ≤ 16−14 ≤ h ≤ 14, −17 ≤ k ≤ 17, −16 ≤ l ≤ 17−17 ≤ h ≤ 15, −27 ≤ k ≤ 26, −32 ≤ l ≤ 32
Reflections collected/unique (Rint)16,844/6888 (0.1459)30,409/8289 (0.0829)64,280/29,898 (0.2535)
Tmax/min.0.967 and 0.8610.965 and 0.6880.989 and 0.803
GOOF on F20.9001.0620.825
Final R1, [I > 2σ(I)], wR2R1 = 0.0821, wR2 = 0.1409R1 = 0.0610, wR2 = 0.1544R1 = 0.0945, wR2 = 0.1375
CCDC23460792340608023406081
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MDPI and ACS Style

Costa, A.G.; Lopes, G.; Rodrigues, J.F.G.; Santos, I.C.; Simão, D.; Lopes, E.B.; Pereira, L.C.J.; Le Breton, N.; Choua, S.; Baudron, S.A.; et al. Cobalt and Iron Cyano Benzene Bis(Dithiolene) Complexes. Crystals 2024, 14, 469. https://doi.org/10.3390/cryst14050469

AMA Style

Costa AG, Lopes G, Rodrigues JFG, Santos IC, Simão D, Lopes EB, Pereira LCJ, Le Breton N, Choua S, Baudron SA, et al. Cobalt and Iron Cyano Benzene Bis(Dithiolene) Complexes. Crystals. 2024; 14(5):469. https://doi.org/10.3390/cryst14050469

Chicago/Turabian Style

Costa, António G., Gonçalo Lopes, João F. G. Rodrigues, Isabel C. Santos, Dulce Simão, Elsa B. Lopes, Laura C. J. Pereira, Nolwenn Le Breton, Sylvie Choua, Stéphane A. Baudron, and et al. 2024. "Cobalt and Iron Cyano Benzene Bis(Dithiolene) Complexes" Crystals 14, no. 5: 469. https://doi.org/10.3390/cryst14050469

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