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Article

Nickel(II) Coordination Polymers Supported by Bis-pyridyl-bis-amide and Angular Dicarboxylate Ligands: Role of Ligand Flexibility in Iodine Adsorption

Department of Chemistry, Chung Yuan Christian University, Chung Li 32023, Taiwan
*
Author to whom correspondence should be addressed.
Int. J. Mol. Sci. 2022, 23(7), 3603; https://doi.org/10.3390/ijms23073603
Submission received: 17 February 2022 / Revised: 14 March 2022 / Accepted: 23 March 2022 / Published: 25 March 2022
(This article belongs to the Collection Frontiers in Polymeric Materials)

Abstract

:
Reactions of N‚N’-bis(3-pyridylmethyl)oxalamide (L1), N‚N’-bis(4-pyridylmethyl)oxalamide (L2), or N,N’-bis(3-pyridylmethyl)adipoamide) (L3) with angular dicarboxylic acids and Ni(II) salts under hydro(solvo)thermal conditions afforded a series of coordination polymers: {[Ni(L1)(OBA)(H2O)]·H2O}n (H2OBA = 4,4-oxydibenzoic acid), 1, {[Ni(L1)(SDA)(H2O)2]·H2O·CH3OH}n (H2SDA = 4,4-sulfonyldibenzoic acid), 2, {[Ni(L2)(OBA)]·C2H5OH}n, 3, {[Ni(L2)(OBA)]·CH3OH}n, 4, {[Ni2(L2)(SDA)2(H2O)3]·5H2O}n, 5, {[Ni2(L2)(SDA)2(H2O)3]·H2O·2C2H5OH}n, 6, {[Ni(L3)(OBA)(H2O)2]·2H2O}n, 7, {[Ni(L3)(SDA)(H2O)2]·2H2O}n, 8, and {[Ni(L3)0.5(SDA)(H2O)2]·0.5C2H5OH}n, 9, which have been structurally characterized by using single-crystal X-ray crystallography. Complex 1 exhibits an interdigitated 2D layer with the 2,4L2 topology and 2 is a 2D layer with the sql topology, while 3 and 4 are 3D frameworks resulting from polycatenated 2D nets with the sql topology and 5 and 6 are 2-fold interpenetrated 3D frameworks with the dia topology. Complexes 7 and 8 are 1D looped chains and 9 is a 2D layer with the 3,4L13 topology. The various structural types in 19 indicate that the structural diversity is subject to the flexibility and donor atom position of the neutral spacer ligands and the identity of the angular dicarboxylate ligands, while the role of the solvent is uncertain. The iodine adsorption of 19 was also investigated, demonstrating that that the flexibility of the spacer L1L3 ligands can be an important factor that governs the feasibility of the iodine adsorption. Moreover, complex 9 shows a better iodine adsorption and encapsulates 166.55 mg g−1 iodine in the vapor phase at 60 °C, which corresponded to 0.38 molecules of iodine per formula unit.

1. Introduction

Coordination polymers (CPs) have rapidly developed into an active area of chemical research, not only for their interesting structures and distinctive topologies, but also potential applications in diverse areas such as gas storage, drug delivery, catalysis, luminescence sensing, and ionic conductivity [1,2,3,4]. The coordinate covalent bonds that link the metal ions and the spacer ligands result in multi-dimensional networks, which are also subject to the nature of hydrogen bonding and other weak interactions. Entanglement is a widely known phenomenon in the crystal engineering of CPs, because the self-assembled structures usually try to fill the space as much as possible to increase the stability of the structure. Three main entanglements involving interpenetration, polycatenation, and self-catenation [5] have been shown, while interdigitation represents that part of an adjacent identical structure is interlaced into the space of the other without interlock. Although many CPs with interesting structures and properties have been reported, the control of their dimensionality and structural type is still a challenge and a great effort is necessary for the ongoing investigation.
Radioactive iodine such as 129I represents one of the most critical fission products in nuclear waste disposal, which has a long radioactive half-life and is harmful to human health. Therefore, these iodine species have to be captured and disposed of effectively [6,7,8]. However, limited adsorption ability, high cost, and environmental issues with the materials under investigation has created demand for developing alternative materials. On the other hand, CPs showing tailorable structures and possessing pores may facilitate iodine adsorption through noncovalent interactions involving iodine and various sorption sites such as amino functionalities [6,7,8].
We have been committed to the synthesis and structural characterization of bis-pyridyl-bis-amide (bpba) ligands containing pyridyl nitrogen atoms and amide groups linked by different—(CH2)n—backbones [9,10,11,12]. Modification of ligand flexibility has been found important in changing the structural diversity. In this report, the L1L3 ligands with different flexibility (Figure 1) were reacted with the metal salts, together with the angular dicarboxylic acid, to explore the structural diversity of nine Ni(II) CPs in mixed-ligand systems. The effect of flexibility and the donor atom position of the spacer ligands on the structural diversity and iodine adsorption were also investigated.

2. Results and Discussion

2.1. Crystal Structure of 1

The single-crystal X-ray diffraction analysis showed that 1 crystallizes in the triclinic space group Pī. The asymmetric unit comprises one Ni(II) cation, one L1 ligand, one OBA2− ligand, and one coordinated and one co-crystallized water molecule. Figure 2a shows the coordination environment of the Ni(II) metal center, which is six-coordinated by two nitrogen atoms from two L1 ligands [Ni-N = 2.064(2) − 2.090(2) Å], three oxygen atoms from two OBA2− ligands [Ni-O = 2.039(16) − 2.195(16) Å], and one oxygen atom from the coordination water [Ni-O = 2.100(17) Å]. The Ni(II) cations are linked by the OBA2− and L1 ligands to form a 2D layer. If the Ni(II) units are defined as 4-connected nodes and the OBA2− as 2-connected nodes, the structure can be simplified as a 2,4-connected net with the 2,4L2 topology (Figure 2b), determined using ToposPro [13]. Figure 2c shows the interdigitation.

2.2. Structure of 2

The crystal structure of 2 was solved in the triclinic space group Pī, revealing that each asymmetric unit consists of one Ni(II) cation, one L1 ligand, one SDA2− ligand, two coordinated and one co-crystallized water molecule, and one MeOH molecule. Figure 3a shows the coordination environment of the Ni(II) metal center, which is six-coordinated by two nitrogen atoms from L1 ligands [Ni-N = 2.104(19) − 2.108(17) Å], four oxygen atoms from two SDA2− ligands [Ni-O = 2.017(14) − 2.049(14) Å], and two coordination water molecules [Ni-O = 2.084(18) − 2.101(17) Å]. The Ni(II) cations are linked by SDA2− and L1 ligands to form a 2D layer. Considering the Ni(II) units as 4-connected nodes, the structure can be simplified as a 4-connected net with the sql topology (Figure 3b).

2.3. Structures of 3 and 4

Structures of 3 and 4 are similar but different in the co-crystallized solvents. Crystals of 3 and 4 conform to the monoclinic space group P21/c and each asymmetric unit contains one Ni(II) cation, one L2 ligand, one OBA2− ligand, and one co-crystallized solvent molecule (EtOH, 3; MeOH, 4). Figure 4a displays a representative coordination environment of the Ni(II) metal center, which is six-coordinated by two nitrogen atoms from two L2 ligands [Ni-N = 2.057(2) and 2.064(2) Å, 3; 2.050(16) and 2.057(16) Å, 4] and four oxygen atoms from two OBA2− ligands [Ni-O = 2.051(17) − 2.207(19) Å, 3; 2.050(14) − 2.209(14) Å, 4]. The Ni(II) cations are linked by OBA2− and L2 ligands to form a 2D layer. If the Ni(II) units are defined as 4-connected nodes, the structure can be simplified as a 4-connected net with the sql topology (Figure 4b), showing a 2D → 3D polycatenation (Figure 4c).

2.4. Structure of 5 and 6

The structures of complexes 5 and 6 are similar but different in the co-crystallized solvents. Single-crystal X-ray diffraction analysis showed that 5 and 6 crystallize in the triclinic space group Pī. Each asymmetric unit consists of two Ni(II) cations, one L2 ligand, one SDA2− ligand, and three coordinated water molecules (two terminal and one bridging), together with five co-crystallized water molecules in 5 and one co-crystallized water molecule and two EtOH molecules in 6, respectively. Figure 5a shows a representative coordination environment of the two Ni(II) metal centers. While the Ni(1) atom is six-coordinated by two nitrogen atoms from two L2 ligands [Ni-N = 2.087(2) and 2.120(2) Å, 5; 2.080(1) and 2.113(19) Å, 6], four oxygen atoms from three SDA2− ligands [Ni-O = 2.083(17) − 2.084(17) Å, 5; 2.020(16) − 2.066(16) Å, 6], and the bridged water molecules [Ni-O = 2.123(17) Å, 5; 2.106(15) Å, 6], the Ni(2) is six-coordinated by six oxygen atoms from three SDA2− ligands [Ni-O = 2.021(18) − 2.029(17) Å, 5; 2.020(16) − 2.041(16) Å, 6] and three coordination water molecules [Ni-O = 2.077(15) − 2.091(17) Å, 5; 2.065(15) − 2.102(18) Å, 6]. The Ni(II) cations are linked by SDA2− and L2 ligands to form a 3D framework. Considering the di-nuclear Ni(II) units as 4-connected nodes, their structures can be simplified as 4-connected nets with the dia topology (Figure 5b), showing the 2-fold interpenetration (Figure 5c).

2.5. Structure of 7

The single-crystal X-ray diffraction analysis showed that 7 crystallizes in the monoclinic space group C2/c, with each asymmetric unit consisting of one Ni(II) cation, one L3 ligand, one OBA2− ligand, and one coordinated and two co-crystallized water molecules. Figure 6a shows the coordination environment of the Ni(II) metal center, which is six-coordinated by two nitrogen atoms from two L3 ligands [Ni-N = 2.100(1) Å], four oxygen atoms from two OBA2− ligands [Ni-O = 2.068(2) − 2.081(4) Å], and two coordinated water molecules [Ni-O = 2.068(2) − 2.081(4) Å]. The Ni(II) cations are linked by OBA2− and L3 ligands to form a 1D looped chain (Figure 6b).

2.6. Structure of 8

Crystals of 8 conform to the monoclinic space group C2/c, with each asymmetric unit consisting of one Ni(II) cation, one L3 ligand, one SDA2− ligand, and two coordinated and two co-crystallized water molecules. Figure 7a shows the coordination environment of the Ni(II) metal center, which is six-coordinated by two nitrogen atoms from two L3 ligands [Ni-N = 2.100(1) Å], four oxygen atoms from two SDA2− ligands [Ni-O = 2.068(2) − 2.081(4) Å], and two coordinated water molecules [Ni-O = 2.068(2) − 2.081(4) Å]. The Ni(II) cations are linked by the SDA2− and the L3 ligands to form a 1D looped chain (Figure 7b).

2.7. Structure of 9

The single-crystal X-ray diffraction analysis showed that 9 crystallizes in the triclinic space group Pī. The asymmetric unit consists of one Ni(II) cation, a half L3 ligand, one SDA2− ligand, two coordinated water molecules, and a half co-crystallized EtOH molecule. Figure 8a shows the coordination environment of the Ni(II) metal center, which is six-coordinated by one nitrogen atom from one L3 ligand [Ni-N = 2.098(2) Å] and five oxygen atoms from two SDA2− ligands [Ni-O = 2.036(17) − 2.169(17) Å], one L3 ligand, and two coordinated water molecules [Ni-O = 2.068(2) − 2.081(4) Å]. The Ni(II) cations are linked by SDA2− and L3 ligands to form a 2D layer. If the Ni(II) cations are defined as 3-connected nodes and the L3 ligand as 4-connected nodes, the structure of 9 can be simplified as a 3,4-connected net with the 3,4L13 topology (Figure 8b).

2.8. Ligand Conformations and Coordination Modes

By calculating the torsion angles of the long carbon chain and evaluating the orientations of the pyridyl rings and carbonyl group, the conformations of the bpba ligands can be expressed as follows [14]: When the torsion angle is 0 ≤ θ ≤ 90°, it is defined as gauche (G), and 90 < θ ≤ 180° as anti (A). Additionally, cis and trans conformations can also be shown if the two C=O groups are in the same and the opposite direction, respectively. Due to the different orientations adopted by the pyridyl nitrogen atoms and the amide oxygen atoms, three more conformations, syn-syn, syn-anti, and anti-anti, can also be found for bpba. Table 1 lists the ligand conformations and coordination modes of the organic ligands in complexes 19. Noticeably, the L1, L2, and L3 ligands in 18 bridge two metal ions through two pyridyl nitrogen atoms, while the L3 ligand of 9 bridges four metal ions through two pyridyl nitrogen atoms and two amide oxygen atoms. The bpba ligands that bridge four metal ions are rare and can be found for the bis(N-pyrid-3-ylmethyl)suberoamide (L) in {[Cd(L)(1,4-NDC)]·2H2O}n (1,4-H2NDC = naphthalene-1,4-dicarboxylic acid) and {[Cd2(L)(1,4-NDC)2]·3H2O}n [15].
The OBA2− and SDA2− ligands show variable coordination modes. In 1, the OBA2− ligand bridges two Ni(II) ions with one chelation mode, while the dicarboxylate ligands in 2 and 79 bridge two Ni(II) ions, and each of the two carboxylate groups coordinates one Ni(II) ion through one oxygen atom. In 3 and 4, the OBA2− ligands bridge two Ni(II) ions with two chelation modes, while in 5 and 6, the SDA2− ligands bridge three Ni(II) ions, leaving one of the carboxylate oxygen atoms uncoordinated. Structural comparisons show that for the complexes with L1 (1 and 2) or L2 (36) ligands, the structural diversity is subject to the change of the angular dicarboxylate ligand, while the solvent is not influential. However, the structural diversity of those containing L3 (79) is subject to the changes of both the angular dicarboxylate ligand and solvent. The different structural types between 8 and 9 demonstrate that the ligand conformation of the flexible L3 is subject to the change of the solvent identity, resulting in AAA-trans-syn-syn and GAG-trans-syn-anti and leading to the formation of a 1D looped chain and 2D layer, respectively.

2.9. PXRD Patterns and Thermal Analysis

The experimental PXRD patterns of complexes 19 (Supplementary Figures S1–S9) match well with their corresponding simulated ones, which demonstrates that the purities of the bulk samples are good enough for further use. On the other hand, thermal gravimetric analysis (TGA) was carried out to examine the thermal decomposition of complexes 19. The TGA curves are shown in Supplementary Figures S10–S18, and Table 2 lists the decomposition temperatures, showing two-step decomposition and indicating that the decomposition temperatures for organic ligands of the frameworks of 3 and 4 with the polycatenated frameworks are much higher among 19.

2.10. Iodine Adsorption

Complexes 79 provide a unique opportunity to investigate the degree of iodine adsorption of bpba-based Ni(II) CPs, which have been executed at 25 and 60 °C and with time intervals of 30, 60, 120, 180, and 360 min, respectively. For each experiment, 0.05 mmol of the complex was placed in a 5 mL sample bottle inside a 50 mL one containing 100 mg of iodine, which was sealed, kept in the oven, and heated. The I2-adsorbed complex was then weighted and the amount of adsorbed I2 was calculated. Each experiment was repeated three times and the results were averaged (Supplementary Tables S1–S6). At 25 °C, the color of complex 7 changed from blue to green, while the color changed from blue to yellow at 60 °C (Supplementary Figure S19). Complex 8 showed no color change at 25 and 60 °C (Supplementary Figure S20), while the color of complex 9 changed from green to dark brown at these two temperatures (Supplementary Figure S21).
Figure 9, Figure 10 and Figure 11 display the average weight changes per gram of 79 upon iodine adsorption at different time intervals and at 25 and 60 °C, respectively, while Table 3 summarizes the results, showing that the adsorption capacities of 7 and 8 are much poorer than 9. With the increase of temperature from 25 to 60 °C, the absorption rate of iodine also showed a good increase for each complex. The different iodine adsorption capacities can be ascribed to their different diversity, which are 1D chains for 7 and 8 and a 2D layer for 9, respectively, showing a maximum adsorption factor of 166.55 mg g−1 for complex 9 at 60 °C for 360 min, corresponding to 0.38 iodine molecules per unit cell. Powder X-ray diffraction (PXRD) patterns of the I2-adsorbed complexes 79 have been measured to confirm their stability. As shown in Supplementary Figures S22–S24, most of the experimental patterns are consistent with the theoretical ones, indicating that these iodine-adsorbed complexes remain stable. Only the PXRD patterns of 8 at 60 °C showed some changes after 180 min.
Energy dispersive X-ray (EDX) analysis of complexes 79 was performed after iodine adsorption (Supplementary Figures S25–S27), confirming the iodine uptake of 79. The iodine-adsorbed samples of 79 can be regarded as the mixtures of iodine and their corresponding complexes. As expected, the amounts of iodine elements were different at three different spots of the samples selected for measurement, indicating the inhomogeneous distribution of iodine in the iodine-adsorbed samples. Table 4 shows the average weights and atomic percentages of the selected elements for the iodine-adsorbed 79, confirming that 9 displays the best iodine adsorption capacity. In addition, experiments have also been performed for complexes 16 to evaluate their iodine adsorption capacities. As shown in Supplementary Figures S28–S33, the colors of 16 remained unchanged at both 25 and 60 °C, indicating minor or no iodine absorption, supported by their EDX data that showed no detectable iodine element (Supplementary Figures S34–S39).
The ability of the CPs to accommodate iodine molecules in the interchain/interlayer space perhaps governs the iodine adsorption capacity [16,17,18]. The solvent accessible volumes calculated by using the PLATON program [19] for 79 were 6.9, 9.3 and 13.7%, respectively, of the unit cell volume, indicating that the 2D 9 may accommodate more iodine than the 1D 7 and 8. However, as shown in Supplementary Table S7, the solvent accessible volumes of complexes 16 were comparable to those of 79, but these CPs revealed no iodine adsorption capacity, demonstrating the important role of the flexibility of the neutral spacer ligands, L1, L2, and L3, in determining the iodine adsorption capacities of 19. The more flexible L3 ligand that resulted in the 2D layer 9 with the 3,4L13 topology may be more susceptible to the changes of the ligand conformation upon the attack of the iodine molecules and thus better to accommodate the iodine molecules. On the other hand, the entangled complexes 16 comprising the rigid L1 and L2 ligands are not vulnerable to the changes of the frameworks upon the iodine attack, allowing undetectable iodine adsorption.

2.11. Gas Adsorption

Low-pressure N2 adsorption and desorption measurements were performed at 77 K for complexes 79, and their isotherms are shown in Supplementary Figures S40–S42, showing a Brunauer–Emmet–Teller (BET) surface area and Langmuir surface of 10.00 and 15.22 m2/g for 7, 9.04 and 14.47 m2/g for 8, and 10.00 and 15.88 m2/g for 9, respectively, indicating similar BET surface areas and Langmuir surfaces.

3. Experimental Section

3.1. General Procedures

Elemental analyses of (C, H, N) were performed on a PE 2400 series II CHNS/O (PerkinElmer Instruments, Shelton, CT, USA) or an Elementar Vario EL-III analyzer (Elementar Analysensysteme GmbH, Hanau, Germany). Infrared spectra were obtained from a JASCO FT/IR-460 plus spectrometer with pressed KBr pellets (JASCO, Easton, MD, USA). Thermal gravimetric analyses (TGA) were carried out on a TG/DTA 6200 over the temperature range of 30 to 900 °C at a heating rate of 10 °C min−1 under N2 (SEIKO Instruments Inc., Chiba, Japan). Powder X-ray diffraction patterns were carried out with a Bruker D8-Focus Bragg-Brentano X-ray powder diffractometer equipped with a CuKα (λα = 1.54178 Å) sealed tube (Bruker Corporation, Karlsruhe, Germany). Gas sorption measurements were conducted using a Micromeritics ASAP 2020 system (Micromeritics Instruments Co., Norcross, GA, USA).

3.2. Materials

The reagent Ni(OAc)2·4H2O was purchased from Alfa Aesar (Ward Hill, MA, USA), and 4,4′-sulfonyldibenzoic acid (H2SDA) and 4,4-oxydibenzoic acid (H2OBA) from Aldrich Chemical Co. (St. Louis, MO, USA). The ligands N,N’-bis(3-pyridylmethyl)oxalamide (L1), N,N’-bis(4-pyridylmethyl)oxalamide (L2), and N,N’-bis(3-pyridylmethyl)adipoamide (L3) were prepared according to published procedures, with some modifications [14].

3.3. Preparations

3.3.1. {[Ni(L1)(OBA)(H2O)]·H2O}n, 1

A mixture of Ni(CH3COO)2·2H2O (0.050 g, 0.20 mmol), L1 (0.027 g, 0.10 mmol), and H2OBA (0.052 g, 0.20 mmol) in 10 mL of H2O was sealed in a 23 mL Teflon-lined steel autoclave, which was heated under autogenous pressure to 100 °C for two days, and then allowed to cool down gradually to room temperature for two days. Green crystals suitable for single-crystal X-ray diffraction were obtained. Yield: 0.023 g (32 %). Anal. Calcd for C28H26N4NiO9 (MW = 621.24): C, 54.13; N, 9.02; H, 4.22 %. Found: C, 53.92; N, 8.97; H, 3.88 %. FT-IR (cm−1): 3567(m), 3372(m), 3224(w), 3056(w), 2937(w), 1676(s), 1594(s), 1509(s), 1423(s), 1392(s), 1230(s), 1164(m), 1102(w), 1008(w), 1005(w), 865(w), 779(w), 705(m), 637(w).

3.3.2. {[Ni(L1)(SDA)(H2O)2]·H2O·CH3OH}n, 2

Complex 2 was prepared by following similar procedures for 1 except that Ni(CH3COO)2·2H2O (0.050 g, 0.20 mmol), L1 (0.027 g, 0.10 mmol), and H2SDA (0.061 g, 0.20 mmol) in 8 mL of H2O and in 2 mL of MeOH were used. Green crystals were obtained. Yield: 0.035 g (49 %). Anal. Calcd for C29H32N4NiO12S (MW = 719.35): C, 48.42; N, 7.79; H, 4.48 %. Found: C, 48.08; N, 7.91; H, 4.34 %. FT-IR (cm−1): 3496(m), 3326(m), 3062(w), 2938(w), 1671(s), 1597(s), 1549(s), 1527(s), 1521(s), 1390(s), 1291(m), 1224(m), 1161(m), 1106(m), 954(w), 864(w), 794(w), 729(s), 617(m).

3.3.3. {[Ni(L2)(OBA)]·C2H5OH}n, 3

Complex 3 was prepared by following similar procedures for 1 except that Ni(CH3COO)2·2H2O (0.050 g, 0.20 mmol), L2 (0.027 g, 0.10 mmol), and H2OBA (0.052 g, 0.20 mmol) in 8 mL of H2O and in 2 mL of EtOH were used. Green crystals were obtained. Yield: 0.036 g (57 %). Anal. Calcd for C30H28N4NiO8 (MW = 631.27): C, 57.08; N, 8.88; H, 4.47 %. Found: C, 56.67; N, 8.54; H, 3.79 %. FT-IR (cm−1): 3454(s), 2370(w), 2305(w), 1671(m), 1623(m), 1515(w), 1503(w), 1418(m), 1225(m), 1153(w), 1065(w), 866(w), 799(w), 648(w).

3.3.4. {[Ni(L2)(OBA)]·CH3OH }n, 4

Complex 4 was prepared by following similar procedures for 1 except that Ni(CH3COO)2·2H2O (0.050 g, 0.20 mmol), L2 (0.027 g, 0.10 mmol), and H2OBA (0.052 g, 0.20 mmol) in 8 mL of H2O and in 2 mL of MeOH were used. Green crystals were obtained. Yield: 0.025 g (41 %). Anal. Calcd for C29H26N4NiO8 (MW = 617.25): C, 56.43; N, 9.08; H, 4.25 %. Found: C, 56.15; N, 8.79; H, 4.51 %. FT-IR (cm−1): 3449(s), 3368(s), 3062(w), 2923(w), 2371(w), 1679(s), 1595(s), 1534(s), 1499(s), 1422(s), 1223(s), 1159(s), 1016(w), 873(m), 776(m), 659(m), 653(m).

3.3.5. {[Ni2(L2)(SDA)2(H2O)3]·5H2O}n, 5

Complex 5 was prepared by following similar procedures for 1 except that Ni(CH3COO)2·2H2O (0.050 g, 0.20 mmol), L2 (0.027 g, 0.10 mmol), and H2SDA (0.061 g, 0.20 mmol) in 10 mL of H2O were used. Green crystals were obtained. Yield: 0.026 g (28 %). Anal. Calcd for C42H46N4Ni2O22S2 (MW = 1140.37): C, 44.24; N, 4.91; H, 4.07 %. Found: C, 43.93; N, 4.73; H, 4.03 %. FT-IR (cm−1): 3440(s), 2369(w), 2318(w), 1638(m), 1516(w), 1401(w), 1165(w), 1045(w), 890(w), 745(w), 697(w).

3.3.6. {[Ni2(L2)(SDA)2(H2O)3]·H22C2H5OH}n, 6

Complex 6 was prepared by following similar procedures for 1 except that Ni(CH3COO)2·2H2O (0.050 g, 0.20 mmol), L2 (0.027 g, 0.10 mmol), and H2SDA (0.061 g, 0.20 mmol) in 8 mL of H2O and in 2 mL of EtOH were used. Green crystals were obtained. Yield: 0.035 g (30 %). Anal. Calcd for C46H50N4Ni2O20S2 (MW = 1160.44): C, 47.61; N, 4.83; H, 4.34 %. Found: C, 47.96; N, 4.81; H, 4.01 %. FT-IR (cm−1): 3709(w), 3636(w), 3478(m), 3392(m), 3231(w), 3058(w), 2923(w), 2054(w), 1680(m), 1636(m), 1558(m), 1509(m), 1400(s), 1284(m), 1159(m), 1097(m), 1012(m), 835(m), 738(s), 617(m).

3.3.7. {[Ni(L3)(OBA)(H2O)2]·2H2O}n, 7

Complex 7 was prepared by following similar procedures for 1 except that Ni(CH3COO)2·2H2O (0.050 g, 0.20 mmol), L3 (0.033 g, 0.10 mmol), and H2OBA (0.052 g, 0.20 mmol) in 8 mL of H2O and 2 mL of MeOH were used. Green crystals were obtained. Yield: 0.048 g (67 %). Anal. Calcd for C32H38N4NiO11 (MW = 713.37): C, 53.88; N, 7.85; H, 5.37 %. Found: C, 53.32; N, 7.73; H, 5.28 %. FT-IR (cm−1): 3502(m), 3250(w), 3076(w), 2923(w), 2372(w), 2305(w), 1636(m), 1600(m), 1541(m), 1384(m), 1227(m), 1156(w), 1026(w), 726(w).

3.3.8. {[Ni(L3)(SDA)(H2O)2]·2H2O}n, 8

Complex 8 was prepared by following similar procedures for 1 except that Ni(CH3COO)2·2H2O (0.050 g, 0.20 mmol), L3 (0.033 g, 0.10 mmol), and H2SDA (0.061 g, 0.20 mmol) in 10 mL of H2O were used. Green crystals were obtained. Yield: 0.035 g (49 %). Anal. Calcd for C32H38N4NiO12S (MW = 761.43): C, 50.48; N, 7.36; H, 5.03 %. Found: C, 50.49; N, 7.04; H, 5.05 %. FT-IR (cm−1): 3530(m), 3488(m), 3253(m), 3068(m), 2931(m), 1637(s), 1554(s), 1384(s), 1295(w), 1158(m), 1101(m), 1014(m), 835(m), 789(m), 745(m), 701(m), 620(m), 557(m).

3.3.9. {[Ni(L3)0.5(SDA)(H2O)2]·0.5C2H5OH}n, 9

Complex 9 was prepared by following similar procedures for 1 except that Ni(CH3COO)2·2H2O (0.050 g, 0.20 mmol), L3 (0.033 g, 0.10 mmol), and H2SDA (0.061 g, 0.20 mmol) in 10 mL of H2O were used. Green crystals were obtained. Yield: 0.038 g (65 %). Anal. Calcd for C24H26N2NiO9.5S (MW = 585.24): C, 49.06; N, 4.79; H, 4.48 %. Found: C, 49.22; N, 4.58; H, 4.47 %. FT-IR (cm−1): 3450(m), 3298(m), 2929(m), 2225(w), 1932(w), 1626(s), 1557(s), 1395(w), 1279(m), 1155(m), 1009(m), 1002(m), 822(m), 736(m), 616(m), 563(m).

3.4. X-ray Crystallography

The phase purities of complexes 19 were verified by using powder X-ray diffraction (PXRD). As shown in Supplementary Figures S1–S9, the experimental PXRD patterns match well with the corresponding simulated ones, indicating that the bulk samples are pure enough.
Single-crystal X-ray diffraction data for complexes 19 were collected on a Bruker AXS SMART APEX II CCD diffractometer with a graphite-monochromated MoKα (λα = 0.71073 Å) radiation at 296 K [20]. Data reduction and absorption correction were performed by using standard methods with well-established computational procedures [21]. Some of the heavier atoms were located by the direct or Patterson method and the remaining atoms were found in a series of different Fourier maps and least-square refinements, while the hydrogen atoms were added by using the HADD command in SHELXTL. Basic information pertaining to crystal parameters and structure refinement is listed in Table 5.

4. Conclusions

Nine Ni(II) coordination polymers containing angular dicarboxylate ligands and bpba ligands with different flexibility and donor atom positions have been synthesized under hydro(solvo)thermal conditions. The various structural types in 19 showed that the structural diversity of these Ni(II) CPs is subject to the flexibility and donor atom position of the bpba ligands and the identity of the angular dicarboxylate ligands. The L3 ligand of 9 adopted a rare coordination mode that bridges four metal ions through two pyridyl nitrogen atoms and two amide oxygen atoms. Complex 9 showed an iodine adsorption factor of 166.55 mg g−1 at 60 °C for 360 min, while that of 7 and 8 was low and 16 showed undetectable iodine adsorption, demonstrating that the flexibility of the bpba ligands is important in governing the iodine adsorption of the bpba-CPs supported by the angular dicarboxylate ligands.

Supplementary Materials

The following are available online at https://www.mdpi.com/article/10.3390/ijms23073603/s1.

Author Contributions

Investigation, W.-T.L.; data curation, T.-T.L.; supervision, J.-D.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Ministry of Science and Technology, Taiwan: MOST 109-2113-M-033-009.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data is contained within the article or supplementary material.

Acknowledgments

We are grateful to the Ministry of Science and Technology of the Republic of China for support.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Structures of the ligands L1L3.
Figure 1. Structures of the ligands L1L3.
Ijms 23 03603 g001
Figure 2. (a) Coordination environment of Ni(II) ion in 1. Symmetry transformations used to generate equivalent atoms: (A) x, y + 1, z − 1; (B) x − 1, y, z. (b) A drawing showing the 2,4L2 topology. (c) A drawing showing the interdigitation.
Figure 2. (a) Coordination environment of Ni(II) ion in 1. Symmetry transformations used to generate equivalent atoms: (A) x, y + 1, z − 1; (B) x − 1, y, z. (b) A drawing showing the 2,4L2 topology. (c) A drawing showing the interdigitation.
Ijms 23 03603 g002
Figure 3. (a) Coordination environment of Ni(II) ion in 2. Symmetry transformations used to generate equivalent atoms: (A) x + 1, y, z + 1; (B) x, y, z − 1. (b) A drawing showing the sql topology.
Figure 3. (a) Coordination environment of Ni(II) ion in 2. Symmetry transformations used to generate equivalent atoms: (A) x + 1, y, z + 1; (B) x, y, z − 1. (b) A drawing showing the sql topology.
Ijms 23 03603 g003aIjms 23 03603 g003b
Figure 4. (a) Coordination environment of the Ni(II) ion in 3 and 4. Symmetry transformations used to generate equivalent atoms: (A) x, y + 1, z. (b) A drawing showing the sql topology. (c) A drawing showing the polycatenation.
Figure 4. (a) Coordination environment of the Ni(II) ion in 3 and 4. Symmetry transformations used to generate equivalent atoms: (A) x, y + 1, z. (b) A drawing showing the sql topology. (c) A drawing showing the polycatenation.
Ijms 23 03603 g004aIjms 23 03603 g004b
Figure 5. (a) Coordination environment of Ni(II) ion in 5 and 6. Symmetry transformations used to generate equivalent atoms: (A) −x + 2, −y + 2, −z − 1; (B) −x + 1, −y + 1, -z for 5 and (A) −x + 1, −y, −z + 1; (B) −x + 2, −y + 1, −z for 6. (b) A drawing showing the dia topology. (c) A drawing showing the 2-fold interpenetration.
Figure 5. (a) Coordination environment of Ni(II) ion in 5 and 6. Symmetry transformations used to generate equivalent atoms: (A) −x + 2, −y + 2, −z − 1; (B) −x + 1, −y + 1, -z for 5 and (A) −x + 1, −y, −z + 1; (B) −x + 2, −y + 1, −z for 6. (b) A drawing showing the dia topology. (c) A drawing showing the 2-fold interpenetration.
Ijms 23 03603 g005aIjms 23 03603 g005b
Figure 6. (a) Coordination environment of Ni(II) ion in 7. Symmetry transformations used to generate equivalent atoms: (A) x + 1/2, −y + 3/2, −z. (b) A drawing showing the 1D structure.
Figure 6. (a) Coordination environment of Ni(II) ion in 7. Symmetry transformations used to generate equivalent atoms: (A) x + 1/2, −y + 3/2, −z. (b) A drawing showing the 1D structure.
Ijms 23 03603 g006aIjms 23 03603 g006b
Figure 7. (a) Coordination environment of Ni(II) ion in 8. Symmetry transformations used to generate equivalent atoms: (A) −x + 1/2, −y + 1/2, −z; (B) −x, y, −z + 1/2. (b) A drawing showing the 1D structure.
Figure 7. (a) Coordination environment of Ni(II) ion in 8. Symmetry transformations used to generate equivalent atoms: (A) −x + 1/2, −y + 1/2, −z; (B) −x, y, −z + 1/2. (b) A drawing showing the 1D structure.
Ijms 23 03603 g007
Figure 8. (a) Coordination environment of Ni(II) ion in 9. Symmetry transformations used to generate equivalent atoms: (A) −x + 1, −y + 2, −z + 2; (B) −x + 1, −y + 1, −z + 1. (b) A drawing showing the 3,4L13 topology.
Figure 8. (a) Coordination environment of Ni(II) ion in 9. Symmetry transformations used to generate equivalent atoms: (A) −x + 1, −y + 2, −z + 2; (B) −x + 1, −y + 1, −z + 1. (b) A drawing showing the 3,4L13 topology.
Ijms 23 03603 g008
Figure 9. Average weight changes of complex 7 upon iodine adsorption.
Figure 9. Average weight changes of complex 7 upon iodine adsorption.
Ijms 23 03603 g009
Figure 10. Average weight changes of complex 8 upon iodine adsorption.
Figure 10. Average weight changes of complex 8 upon iodine adsorption.
Ijms 23 03603 g010
Figure 11. Average weight changes of complex 9 upon iodine adsorption.
Figure 11. Average weight changes of complex 9 upon iodine adsorption.
Ijms 23 03603 g011
Table 1. Ligand conformations and bonding modes of 19.
Table 1. Ligand conformations and bonding modes of 19.
ComplexesConformationCoordination Mode
1 Ijms 23 03603 i001
trans-anti-anti
Ijms 23 03603 i002
μ2-κOκO’:κO’’
2 Ijms 23 03603 i003
trans-syn-anti
Ijms 23 03603 i004
μ2-κO:κO’
3, 4 Ijms 23 03603 i005
trans
Ijms 23 03603 i006
μ2-κOκO’:κO’’κO’’’
5, 6 Ijms 23 03603 i007
trans
Ijms 23 03603 i008
μ3-κO:κO’:κO’’
7 Ijms 23 03603 i009
AAA-trans-syn-syn
Ijms 23 03603 i010
μ2-κO:κO’
8 Ijms 23 03603 i011
AAA-trans-syn-syn
Ijms 23 03603 i012
μ2-κO:κO’
9 Ijms 23 03603 i013
GAG-trans-syn-anti
Ijms 23 03603 i014
μ2-κO:κO’
Table 2. Thermal properties of complexes 19.
Table 2. Thermal properties of complexes 19.
ComplexWeight Loss of Solvent
°C (Calc/Found), %
Weight Loss of Ligand
°C (Calc/Found), %
12 H2OL1 + (OBA2−)
~220 (5.79/6.71)240 − 800 (85.31/84.28)
2MeOH + H2O
~220 (11.96/10.56)
L1 + (SDA2−)
240 − 800 (80.07/81.29)
3EtOHL2 + (OBA2−)
~300 (7.29/4.52)310 − 800 (85.86/84.77)
4MeOH + H2O
~130 (5.11/5.62)
L2 + (OBA2−)
290 − 800 (90.82/88.14)
58 H2OL2 + 2 (SDA−2)
~180 (12.67/10.20)270 − 800 (77.34/78.28)
62 EtOH + H2O
~170 (10.44/13.13)
L2 + 2 (SDA−2)
200 − 800 (76.00/78.63)
74 H2O
~200 (10.09/9.97)
L3 + (OBA2−)
260 − 800 (82.14/82.12)
84 H2O
~160 (9.40/9.71)
L3 + (SDA2−)
230 − 800 (77.57/76.96)
90.5 EtOH + 2 H2O
~220 (10.08/9.26)
0.5 L3 + (SDA2−)
240 − 900 (80.13/83.25)
Table 3. Average adsorbed iodine (mg g−1) for complexes 79 at different time intervals (min) and temperatures.
Table 3. Average adsorbed iodine (mg g−1) for complexes 79 at different time intervals (min) and temperatures.
7 8 9
Time25 °C60 °C25 °C60 °C25 °C60 °C
300.2080.3790.2580.60622.73107.92
600.3790.5490.6061.29863.72140.64
1200.5210.5870.9521.558118.93161.30
1800.5870.6061.2981.558159.75165.15
3600.6060.6061.3851.558163.14166.55
Table 4. Average weight (%) from EDX for complexes 79.
Table 4. Average weight (%) from EDX for complexes 79.
Element789
C56.9355.7049.45
O23.5422.0425.66
Ni11.3411.079.68
I0.420.017.03
Table 5. Crystallographic data for 19.
Table 5. Crystallographic data for 19.
Compound123
FormulaC28H26NiN4O9C29H32NiN4O12SC30H28NiN4O8
Formula weight621.24719.35631.27
Crystal systemTriclinicTriclinicMonoclinic
Space groupPīPīP21/c
a, Å10.2625(9)12.0618(3)10.4220(4)
b, Å10.7071(9)12.5407(3)13.7045(5)
c, Å13.8202(12)12.6199(3)19.3529(7)
α, °70.272(5)110.7299(12)90
β, °89.128(5)99.6766(12)91.645(2)
γ,°81.387(5)108.9309(12)90
V, Å31412.3(2)1595.49(7)2763.00(18)
Z224
Dcalc, Mg/m31.4611.4971.518
F(000)6447481312
µ(Mo Kα), mm−10.7480.7430.763
Range(2θ) for data collection,deg1.566 ≤≤ 2θ ≤ 25.9991.821 ≤ 2θ ≤ 28.3081.821 ≤ 2θ ≤ 26.000
Independent reflections5528
[R(Int) = 0.0234]
7907
[R(Int) = 0.0235]
5427
[R(Int) = 0.0300]
Data/restraints/parameters5528/0/3797907/1/4425427/6/385
quality-of-fit indicatorc1.0451.0451.053
Final R indices
[I > 2σ(I)] a,b
R1 = 0.0384,
wR2 = 0.0978
R1 = 0.0408,
wR2 = 0.1196
R1 = 0.0407,
wR2 = 0.1109
R indices (all data)R1 = 0.0500,
wR2 = 0.1039
R1 = 0.0510,
wR2 = 0.1271
R1 = 0.0494,
wR2 = 0.1163
Compound456
FormulaC29H26NiN4O8C42H46Ni2N4O22S2C46H50Ni2N4O20S2
Formula weight617.251140.371160.44
Crystal systemMonoclinicTriclinicTriclinic
Space groupP21/cPīPī
a, Å10.3888(3)11.6188(10)11.5864(5)
b, Å13.6881(4)12.3844(10)12.3663(5)
c, Å19.0647(7)19.5572(16)19.3944(8)
α, °9080.487(5)82.136(2)
β, °92.4267(17)87.616(5)87.810(2)
γ,°9063.355(4)63.543(2)
V, Å32708.63(15)2479.0(4)2463.61(18)
Z422
Dcalc, Mg/m31.5141.5281.564
F(000)128011801204
µ(Mo Kα), mm−10.7770.9290.743
Range(2θ) for data collection,deg1.8332 ≤ 2θ ≤ 28.2871.865 ≤ 2θ ≤ 28.4341.821 ≤ 2θ ≤ 26.000
Independent reflections6700
[R(Int) = 0.0197]
12315
[R(Int) = 0.0317]
12260
[R(Int) = 0.0216]
Data/restraints/parameters6700/0/37912315/0/65112260/6/667
quality-of-fit indicator c1.0471.0301.048
Final R indices
[I > 2σ(I)] a,b
R1 = 0.0395,
wR2 = 0.1102
R1 = 0.0448,
wR2 = 0.1244
R1 = 0.0412,
wR2 = 0.1239
R indices (all data)R1 = 0.0440,
wR2 = 0.1132
R1 = 0.0616,
wR2 = 0.1345
R1 = 0.0455,
wR2 = 0.1273
Compound789
FormulaC32H38NiN4O11C32H38NiN4O12SC24H26NiN2O9.5S
Formula weight713.37761.43585.24
Crystal systemMonoclinicMonoclinicTriclinic
Space groupC2/cC2/cPī
a, Å20.2189(10)19.5355(6)7.1192(2)
b, Å9.4113(5)9.5220(3)11.0064(3)
c, Å18.7496(9)19.2870(5)17.0108(5)
α, °909089.7201(17)
β, °102.6301(18)103.1949(11)78.8806(18)
γ,°909081.4570(19)
V, Å33481.5(3)3492.99(18)1292.99(6)
Z442
Dcalc, Mg/m31.3611.4481.503
F(000)14961592608
µ(Mo Kα), mm−10.6200.6830.888
Range(2θ) for data collection,deg2.226 ≤ 2θ ≤ 25.9982.169 ≤ 2θ ≤ 28.2861.872 ≤ 2θ ≤ 28.356
Independent reflections3424
[R(Int) = 0.0465]
4322
[R(Int) = 0.0292]
6421
[R(Int) = 0.0431]
Data/restraints/parameters3424/0/2364322/1/2366421/3/353
quality-of-fit indicator c1.0361.0691.039
Final R indices
[I > 2σ(I)] a,b
R1 = 0.0532,
wR2 = 0.1488
R1 = 0.0371,
wR2 = 0.0976
R1 = 0.0440,
wR2 = 0.0977
R indices (all data)R1 = 0.0646,
wR2 = 0.1645
R1 = 0.0439,
wR2 = 0.1038
R1 = 0.0760,
wR2 = 0.1089
a R1 = ∑||Fo| − |Fc||/∑|Fo|. b wR2 = [∑w(Fo2 − Fc2)2/∑w(Fo2)2]1/2. w = 1/[σ2(Fo2) + (ap)2 + (bp)], p = [max(Fo2 or 0) + 2(Fc2)]/3. a = 0.0511, b = 0.0836 for 1. a = 0.0725, b = 0.7345 for 2. a = 0.0407, b = 0.0494 for 3; a = 0.0395, b = 0.0440 for 4. a = 0.0448, b = 0.0616 for 5. a = 0.0412, b = 0.0455 for 6; a = 0.0532, b = 0.0646 for 7. a = 0.0371, b = 0.0439 for 8. a = 0.0440, b = 0.0760 for 9. c quality-of-fit = [∑w(|Fo2| − |Fc2|)2/Nobserved − Nparameters)]1/2.
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Lee, W.-T.; Liao, T.-T.; Chen, J.-D. Nickel(II) Coordination Polymers Supported by Bis-pyridyl-bis-amide and Angular Dicarboxylate Ligands: Role of Ligand Flexibility in Iodine Adsorption. Int. J. Mol. Sci. 2022, 23, 3603. https://doi.org/10.3390/ijms23073603

AMA Style

Lee W-T, Liao T-T, Chen J-D. Nickel(II) Coordination Polymers Supported by Bis-pyridyl-bis-amide and Angular Dicarboxylate Ligands: Role of Ligand Flexibility in Iodine Adsorption. International Journal of Molecular Sciences. 2022; 23(7):3603. https://doi.org/10.3390/ijms23073603

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Lee, Wei-Te, Tsung-Te Liao, and Jhy-Der Chen. 2022. "Nickel(II) Coordination Polymers Supported by Bis-pyridyl-bis-amide and Angular Dicarboxylate Ligands: Role of Ligand Flexibility in Iodine Adsorption" International Journal of Molecular Sciences 23, no. 7: 3603. https://doi.org/10.3390/ijms23073603

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