Two CdII-containing coordination polymers based on trinuclear and dodecanuclear clusters

Inorganic Chemistry Communications 70 (2016) 90–94

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Two CdII-containing coordination polymers based on trinuclear and dodecanuclear clusters Yuehong Tao, Xueqin Zhou, Zikai Wang, Ying Shi, Yao Guo, Hua Wu ⁎ Jiangsu Key Laboratory of Pesticide Sciences, College of Sciences, Nanjing Agricultural University, Nanjing 210095, Jiangsu, China

a r t i c l e

i n f o

Article history: Received 23 April 2016 Received in revised form 20 May 2016 Accepted 21 May 2016 Available online 24 May 2016 Keywords: Coordination polymer Trinuclear clusters Dodecanuclear clusters Tris(4-(1H-imidazol-1-yl)phenyl)amine

a b s t r a c t Two new metal-organic coordination polymers, namely, [Cd3(Tipa)2(1,2,3-btc)2]·2H2O·0.5(C2H5OH) (1) and [Cd6(Tipa)2(1,2,3-btc)4(H2O)3]·3H2O (2), where 1,2,3-btc = benzene-1,2,3-tricarboxylic anion and Tipa = tris(4-(1H-imidazol-1-yl)phenyl)amine, have been synthesized under hydrothermal conditions with Cd(AcO)2, CdCl2 or CdSO4. Single-crystal X-ray structure analysis reveals that compounds 1–2 show different three dimensional (3D) frameworks based on trinuclear and dodecanuclear cadmium clusters, respectively. For compound 1, the Tipa ligands bridge the trinuclear cadmium clusters in bi-dentate and tri-monodentate modes to give a 3D (3,6)-connected framework with the short Schläfli symbol of (62·4)(612·43). For compound 2, all Tipa and 1,2,3-btc ligands connected dodecanuclear cadmium clusters to generate a rare 3D uninodal tenconnected topology with the short Schläfli symbol of 312·428·55. Moreover, the infrared spectra, elemental analyses, thermogravimetric analysis, and luminescent properties for the two compounds were also investigated. © 2016 Elsevier B.V. All rights reserved.

Contents Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 Appendix A. Supplementary material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

Constructions of metal-organic coordination polymers based on crystal engineering have been achieved significant progress in the field of state-of-the-art material science, not only because their supramolecular architectures with intriguing topology, but also for their potential applications in gas separation and storage, chemical sensors, catalysis, optics, magnetism and proton conduction [1]. In recent years, metal-organic coordination polymers with specific topological structures and functionalities have been constructed by judiciously selecting SBUs (secondary building units) and linkers, which are certified by many examples achieved directly to the assembly of frameworks [2]. Currently, many researches indicate that the construction and design of coordination polymers involved many examples can be influenced by many pivotal factors in the molecular assembly and crystallization processes, such as the elaborate selection of organic ligands, the metal ions, the reaction temperature, the pH value, the

⁎ Corresponding author. E-mail address: [email protected] (H. Wu).

http://dx.doi.org/10.1016/j.inoche.2016.05.022 1387-7003/© 2016 Elsevier B.V. All rights reserved.

counter ions, the metal-to-ligand ratio, the template, and so on [3]. Although some crucial factors are explored well enough relatively in controlling the diversity of structures, how to build target frameworks of coordination polymers with anticipated structures is still a challenge. It is well known that multinuclear metal clusters as SBUs were employed constantly as an effective synthetic strategy to construct metal-organic coordination polymers with highly connected nets. Owing to the fact that some high connected examples of 10-, 12-, and 14-connected frameworks have been reported based on main tetranuclear, pentanuclear and dodecanuclear [4]. However, the uninodal topological samples of highly connected nets are still limited relative to various coordination modes. Generally, it is an effective approach to the synthesis of high-nuclear clusters by selecting organic ligands elaborately with more coordination sites, such as carboxylate ligands, N-donor ligands and their derivatives. In this work, the long semi-flexible N-donor ligand of tris(4-(1H-imidazol-1-yl)phenyl)amine (Tipa) with three arms can rotate around the central N moiety, and benzene-1,2,3-tricarboxylic acid with potential adjacent carboxylate coordination sites and easy to form multinuclear metal clusters were

Y. Tao et al. / Inorganic Chemistry Communications 70 (2016) 90–94

Fig. 1. (a) The coordination environments of the CdII atoms in 1. The uncoordinated solvent molecules and H atoms are omitted for clarity. Symmetry code: #1 -x-1, -y+2, z; #2 x-2, -y+ 1, -z; #3 x-1, y-1,z-1; #4 x-1, y, z-1. (b) The trimetallic subunit of CdII atoms in compound 1. (c) The 1D chain and 2D layer of compound 1. (d) Schematic representation of the 3,6-connected net with a (62·4)(612·43) topology. The blue and purple spheres represent the Tipa ligands and trimetallic CdII subunits, respectively.

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selected in the synthesized system. Finally, two coordination polymers of [Cd3(Tipa)2(1,2,3-btc)2]·2H2O·0.5(C2H5OH) (1) and [Cd6(Tipa)2(1,2,3-btc)4(H2O)3]·3H2O (2) (1,2,3-btc = benzene-1,2,3tricarboxylic anion) with 3,6-connected and 10-connected nets have been built from linear trinuclear and boat-shaped dodecanuclear Cdclusters, respectively. Further, the photoluminescent properties of the coordination polymers have also been studied. Compounds 1 and 2 are prepared by reactions of CdII ions, Tipa ligands and benzene-1,2,3-tricarboxylic anions under approximate solvothermal conditions, and the starting materials of cadmium salt are different for the Cd(AcO)2 of 1 [5] and CdCl2 or CdSO4 of 2 [6], respectively. Single-crystal X-ray analysis reveals that two compounds crystallize in the triclinic system with P-1 space groups (Table S1) [7], and selected bond distances and angles are listed in Table S2. The asymmetric unit of compound 1 contains three crystallographically unique CdII atoms, two unique 1,2,3-btc anions, two Tipa ligands, two uncoordinated water molecules, and a half free C2H5OH solvent molecule (Fig. 1a). Each 1,2,3-btc anion acts as a μ4-bridge to link four CdII ions through its three adjacent carboxylate groups. The Cd1 and Cd2 atoms are all sixcoordinated by five oxygen atoms from two different 1,2,3-btc anions and one nitrogen atom from Tipa ligand in distorted pentagonal pyramidal geometries. Cd3 atom shows a slightly distorted octahedral coordination sphere, completed by four oxygen atoms from two different 1,2,3-btc anions and two nitrogen atoms from two Tipa ligands. Two opposing positions in the octahedron are taken up by one imidazole N atom and one carboxylate O atom. The Cd\\O bonds distances vary from 2.203(2) to 2.573(2) Å, and the \\Cd\\O angles are in the range from 55.86° to 152.22°, which are similar to previously reported works [11]. Each Cd3 ion bridges Cd1 and Cd2 ions by coordinating O atoms from carboxylate groups to form a trimetallic subunit (Fig. 1b). Within the trimetallic subunit, the intermetallic distance of Cd1···Cd3 and Cd3···Cd2 are 3.838 and 3.849 Å, respectively. The trimetallic subunits are connected by carboxylate groups to form an infinite one-dimensional (1D) chain structure along the c-axis as shown in Fig. 1c (right). The Tipa ligands containing N10 atom in bi-dentate modes bridge the 1D chain to give a 2D layer (Fig. 1c, left), and remainder Tipa ligands containing N1 atom in tri-monodentate modes connect the layers into a 3D framework (Fig. S1). To better understand the complicated 3D structure of 1, topological analysis is carried out. The tri-monodentate Tipa ligand can be considered as a 3-connected node, the bi-monodentate Tipa and 1,2,3-btc anions can be considered as links, and the above-mentioned trimetallic subunit can be viewed as a six-connected node. Therefore, the structure of 1 is a 3D (3,6)-connected framework with Schläfli symbol of (62·4)(612·43) (Fig. 1d). The structure of 2 contains six unique CdII atoms, four unique 1,2,3btc anions, two unique Tipa ligands, and six water molecules as shown in Fig. 2a. Cd1 and Cd4 atoms are all six-coordinated by five carboxylate oxygen atoms from three 1,2,3-btc anions, and one nitrogen atom from Tipa ligand in distorted octahedral coordination geometries with one imidazole N and one carboxylate O atoms at the apical positions. Cd2 atom is six-coordinated by five O atoms from two 1,2,3-btc anions and two water molecules at the apical positions and one nitrogen atom form Tipa ligand in a distorted octahedral coordination geometry. Cd3 atom is seven-coordinated by seven O atoms from four different 1,2,3btc anions, and displays a distorted pentagonal-bipyramidal coordination geometry. Cd5 atom is six-coordinated by one nitrogen atom from Tipa ligand, four O atoms from four different carboxylate groups of three 1,2,3-btc anions, and one water molecule in distorted octahedral coordination geometry. Cd6 atom is five-coordinated by five O atoms from four different carboxylate groups of three 1,2,3-btc anions in a distorted square-pyramid geometry. The Cd\\O bond lengths are slightly different, ranging from 2.155(4) to 2.614(3) Å. Although the bond lengths of Cd3\\O18 and Cd3\\O14 are obviously different from others, they are within the normal ranges and consistent with those described in the literature [11].

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Y. Tao et al. / Inorganic Chemistry Communications 70 (2016) 90–94

Interestingly, there are fourteen μ2–Ocarboxylate groups, which connect twelve CdII atoms to form a novel boat-shaped Cd12 cluster, with non-bonding Cd···Cd distances ranging from 3.591(2)–3.806(2) Å (Fig. 2b). The Cd12 cluster is enveloped by the 1,2,3-btc anions and

Fig. 2. (a) The coordination environment of the CdII atoms in 2. The uncoordinated water molecule and H atoms are omitted for clarity. Symmetry codes: #1 x-1, y, z; #2 -x+1, y+1, -z; #3 -x+1, -y+2, -z-1; #4 x+1, y-1, z; #5 -x+2, -y +1, -z-1. (b) The Cd12cluster in 2. (c) Schematic representation of topology of the ten-connected Cd12 cluster. (d) The 3D 10-connected topological network of 2 with the short Schläfli symbol of 312·428·55.

Tipa ligands. As is illustrated in Fig. 2c, each Cd12-based building cluster is linked to ten adjacent Cd12 clusters through twelve 1,2,3-btc anions and eight Tipa in bidentate bridging modes. The 1,2,3-btc bridging ligands have been fully deprotonated. To simplify the network of 2, each Cd12-cluster can be considered as a uninodal 10-connected node, each two bi-dentate Tipa ligands can be considered as one linker, and each two 1,2,3-btc ligands can be considered as another linker. As a result, the ten-connected of 2 can be described as being formed from parallel 36 nets in the crystallographic ac plane with each two Cd12 centers distances of 13.30, 19.62 and 21.38 Å, respectively. Moreover, another four Cd12 centers are distributed to up and down of the 36 net with each two of the Cd12 centers distances of 21.86 and 21.99 Å, respectively (Fig. 2c). Therefore, the whole 3D framework of 2 can be simplified as a uninodal ten-connected coordination network based on twelve nuclear cadmium clusters with the short Schläfli symbol of 312·428·55 (Fig. 2d and Fig. S2). According to previous documents, only a few examples of 10-connected architectures have been observed for topological systems [4]. However, most of the studies have been focused on the binodal fashion of (3,10)-connected nets based on tri-, tetra- and penta-nuclear metal clusters in bisnodal, the 10-connected coordination works in uninodal fashions were rare up to now. Currently, although some Cd-containing coordination compounds based on Tipa ligand and different carboxylic anions have been synthesized and characterized, their structures are very different. The carboxylic acids of 5-NH2-1,3-benzenedicarboxylic acid, 5-OH-1,3benzenedicarboxylic acid, fumaric acid, 4,4′-oxybis(benzoic acid), 1,4benzenedicarboxylic acid have been used to construct Cd-containing compounds with Tipa ligand [12]. However, their structures are mainly focused on the exhibitions of various entangled characters, the metalcluster as the SBUs connecting the frameworks have not been reported. According to the above structural analyses, it can be known that the bridged modes of benzene-1,2,3-tricarboxylic anion (Scheme 1) are different in the compounds 1 and 2, which results in the diverse structures of the two compounds. From the structure descriptions, we found the carboxylate groups of the rigid 1,2,3-btc anions exhibit a variety of coordination modes. There are five kinds of coordination modes of the carboxylate groups. The carboxylate groups show μ4-η1:η2:η1:η1:η1:η1 (mode I, Scheme 1) coordination mode in 1. Whereas, in 2, the carboxylate groups adopts four coordination modes of μ4-η2:η1:η1:η0:η1:η1 (mode II), μ5-η1:η1:η1:η2:η2:η1 (mode III), μ6-η1:η1:η2:η2:η1:η1 (mode IV), and μ4-η1:η1:η2:η0:η2:η1 (mode V). Clearly, the diverse coordination modes of the carboxylate groups resulted in the different type of CdII-clusters, and further lead to the structural differences of compounds 1–2. The photoluminescent spectra of compounds 1 and 2, and free ligands (1,2,3-btc and Tipa) were examined in the solid state at room temperature. The emission and excitation peaks of the compounds are shown in Fig. 3 and Table S3. Emission bands were observed at 296 (λex = 241 nm) and 420 nm (λex = 365 nm) for 1,2,3-H3btc and Tipa ligands, respectively. The emission bands for the free ligands are probably attributable to the π* → n or π* → π transitions [13]. Compounds 1–2 display fluorescence at room temperature. For compounds 1 and 2, the emission peaks were observed at 450 nm (λex = 380 nm) and 470 nm (λex = 375 nm), respectively. Notably, to compare with 1,2,3-H3btc and Tipa ligands, the absorption spectra of compounds 1 and 2 are obviously red-shifted. Because the CdII ion is difficult to oxidize or to reduce due to the d10 configuration, the emission spectra are neither metal-to-ligand charge transfer (MLCT) nor ligandto-metal charge transfer (LMCT) in nature [14]. This result indicates that the photoluminescence may be attributed to a mixture characteristics of intraligand and ligand-to-ligand charge transition (LLCT), as reported for other CdII complexes with mixed O-donor and N-donor ligands [15]. The different red-shifts of 1 and 2 may be attributed to diverse coordination modes of CdII ions with the 1,2,3-btc and Tipa ligands.

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Scheme 1. Coordination modes of the 1,2,3-btc anions in compounds 1–2.

Fig. 3. Emission spectra of free ligands and 1–2 at room temperature.

To characterize the compounds 1 and 2 in terms of thermal stability, their thermal behaviors were studied by thermogravimetric analysis (TGA). The experiments were performed on samples consisting of numerous single crystals of 1 and 2 under N2 atmosphere with a heating rate of 10 °C/min (Fig. S3). The first weight losses corresponding to the release of water molecules are observed before 148 °C for compound 1 (obsd 4.9%, calcd 3.89%) and 196 °C for compound 2 (obsd 5.4%, calcd 4.32%). The departure of organic components occurred from 305 to 538 °C for compound 1, 262–515 °C for compound 2. The remaining weight of 1 and 2 may correspond to the formation of CdO. In conclusion, two CdII coordination polymers with a flexible tridentate ligand and same carboxylate anions have been prepared and characterized through single-crystal X-ray diffraction analyses. The two compounds display fascinating 3D frameworks of 3.6- and 10-connected based on linear trinuclear and boat-shaped dodecanuclear Cd-clusters respectively. The results indicate the importance of the flexible tri(4-imidazolylphenyl)amine ligand and carboxylate anions in the construction of the final frameworks.

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Acknowledgments This work was supported by the National Natural Science Foundation of China (grant no. 21371098), the Natural Science Foundation of Jiangsu Province (no. BK20131314), the Fundamental Research Fund for the Central Universities (KYZ201323), the Jiangsu Postdoctoral Science Foundation (no. 1401007C), the China Postdoctoral Science Foundation (no. 2015M570430) and the support for State Key Laboratory of Coordination Chemistry of Nanjing University.

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Appendix A. Supplementary material Electronic supplementary information (ESI) available: X-ray crystallographic data in CIF format, Fig. S1–3, Table S1–3 for compounds 1 and 2. CCDC reference numbers are 1470166-1470167. Copy of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax: int code + 44(1223)336-033; E-mail: [email protected]]. Supplementary data associated with this

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Y. Tao et al. / Inorganic Chemistry Communications 70 (2016) 90–94 1456 (s), 1380 (s), 1306 (m), 1124 (m), 1064 (s), 964 (m), 936 (m), 833 (s), 769 (m), 715 (m), 548 (m). For 2, the synthetic method is similar to 1, except the starting materials of Cd(AcO)2 in 1 was used instead of CdSO4·4H2O (0.084 g, 0.3 mmol) or CdCl2·2.5H2O (0.068 g, 0.3 mmol) with a yield of 48%. Anal. Calcd for C90H67Cd6N14O30 (Mr = 2499.04): C, 43.26%; H, 2.70%; N, 7.85%. Found: C, 42.19%; H, 2.75%; N, 7.89%. IR data (KBr, cm−1): 3410 (m), 3124 (m), 1607 (m), 1557 (m), 1516 (s), 1456 (m), 1379 (s), 1306 (w), 1123 (w), 1063 (m), 961 (w), 833 (m), 769 (m), 714 (m), 655 (m), 617 (w), 540 (w). Diffraction intensities for 1 and 2 were recorded on an Oxford Diffraction Gemini R Ultra diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 A) at 293 K. The structures were solved with the direct method of SHELXS-97 [8] and refined with full-matrix least-squares techniques using the SHELXL-97 program [9] within WINGX [10]. The hydrogen atoms attached to carbons were generated geometrically. The hydrogen atom positions were fixed geometrically at calculated distances and allowed to ride on the parent atoms. The disordered atoms C48–71, N9–12, N48 and O16 of compound 1 were refined using the atoms split over two sites. Non-hydrogen atoms were refined with anisotropic temperature parameters except C65, C67, C69–70 and O16 of 1, and C47 of 2. G.M. Sheldrick, SHELXS-97, Programs for X-ray Crystal Structure Solution, University of Göttingen, Göttingen, Germany, 1997. G.M. Sheldrick, SHELXL-97, Programs for X-ray Crystal Structure Refinement, University of Göttingen, Göttingen, Germany, 1997. L.J. Farrugia, WINGX, a Windows Program for Crystal Structure Analysis, University of Glasgow, Glasgow, U.K., 1988 (a) M. Du, X.-J. Jiang, X.-J. Zhao, Inorg. Chem. 46 (2007) 3984; (b) C.N.R. Rao, S. Natarajan, R. Vaidhyanathan, Angew. Chem. Int. Ed. 43 (2004) 1466;

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