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CoII and ZnII Coordination Frameworks with Benzene-1,2,3-tricarboxylate Tecton and Flexible Dipyridyl Co-Ligand: A New Type of Entangled Architecture and a Unique 4-Connected Topological Network Lu-Fang Ma,† Cheng-Peng Li,‡ Li-Ya Wang,*,† and Miao Du*,‡ † ‡
College of Chemistry, Chemical Engineering, Luoyang Normal University, Luoyang 471022, P. R. China College of Chemistry and Life Science, Tianjin Key Laboratory of Structure and Performance for Functional Molecule, Tianjin Normal University, Tianjin 300387, P. R. China
bS Supporting Information ABSTRACT: Hydrothermal reactions of CoII or ZnII acetate with benzene-1,2,3tricarboxylic acid (H3bta) and 1,2-bi(4-pyridyl)ethane (bpa) afford two unique metalorganic frameworks, in which 1 represents a new type of entangled architecture formed via polycatenane of a pair of (4,4) net with one twodimensional 3-connected self-interpenetrating pattern, while 2 shows a threedimensional 4-connected net with a new trinodal topology.
onsiderable attention has recently been focused on the field of interpenetrating and self-penetrating coordination frameworks, owing to their special importance in the area of entangled systems and fascinating topological and physical properties.1,2 Interpenetration is one of the most familiar types of entanglements, which can be viewed as a series of independent nets that penetrate mutually.3 In contrast, self-penetrating supramolecular nets, in which the rods of frameworks penetrate through the shortest internodal circuits, are quite rare.4 Significantly, although both interpenetrating and self-penetrating coordination nets have been reported, the topological framework containing both types of entangled motifs within the same crystalline lattice has been very rare so far.5 Therefore, it is a great challenge to synthesize the entangled systems displaying both interpenetrating and self-penetrating structural characters. On the other hand, the topological analysis of metalorganic frameworks (MOFs) has been a topical research area, not only for the importance of simplifying the complicated structures of coordination polymers but also for the instructive role in further rational design of predicted functional crystalline materials. Nodes of 3-, 4-, and 6-connectivity are of most relevance,6 and a variety of such uninodal topological networks have been realized by three-dimensional (3D) MOFs, for instance, dia (which have four-connected, essentially tetrahedral nodes), nbo (which has square-planar nodes with a 90° twist along every connection), cds (which is a 4-connected net with the minimum number of vertices in the repeat unit), pcu (the primitive cubic lattice is the only one with regular octahedral coordination.), etc.7
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However, other types of 3- and 4-connected networks have scarcely been reported so far. Thus, the construction of such new network topologies is of great interest at the current stage. Recently, we have been successful in the construction of two two-dimensional (2D) coordination polymers with unique 4- and 6-connected topological nets using the flexible dipyridyl and isophthalate organic tectons.8 Compared with the widely used 1,3-benzene dicarboxylic acid, 1,3,5-benzenetricarboxylic acid, and 1,2,4,5-benzenetetracarboxylic acid, benzene-1,2,3-tricarboxylic acid (H3bta) has distinctive characteristics such as the different distribution of carboxylate groups as well as the versatile coordination capability of forming both short bridges via the carboxylates and long bridges via the benzene ring. In this context, our synthetic strategy is to fabricate novel topological networks by assembly of mixed ligands H3bta and 1,2-bi(4pyridyl)ethane (bpa) with different metal ions, and we will describe here two new 3- and 4-connected frameworks {[Co2(bpa)1.5(bta)(H2O)4][Co(bpa)(bta)](H2O)0.5}n (1) and [Zn2(bta)(OH)(bpa)]n (2). Notably, complex 1 not only shows a new 3-connected network topology but also represents the first entangled framework incorporating both self-interpenetration and polycatenated patterns of different types that exist simultaneously in the same crystal. Received: March 23, 2011 Revised: July 2, 2011 Published: July 12, 2011 3309
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Crystal Growth & Design
Figure 1. Views of 1. (a) Puckered negative (4,4) layer of [Co(bpa)(bta)]2 (motif A). (b) The positive layer of [Co2(bpa)1.5(bta)(H2O)4]+ (motif B). (c) The (6,3) net observed in motif B. (d) Schematic representation of the self-penetrating network of motif B. Three identical (6,3) layers (yellow, blue, and red parts) interlocked with each other are joined together by the semicircle Co1bpa chains (green part).
Reactions of H3bta, bpa, KOH, with CoII or ZnII acetate under hydrothermal conditions produce complexes 1 and 2,9,10 which have been characterized by IR spectra and microanalysis.‡ Single-crystal X-ray characterization indicates that complex 1 comprises two crystallographically distinct 2D polymeric motifs, that is, the puckered negative (4,4) layer of [Co(bpa)(bta)]2 (motif A, see Figure 1a) and the positive layer of [Co2(bpa)1.5(bta)(H2O)4]+ with a self-penetrating feature (motif B, see Figure 1b). In this case, there are three crystallographic independent CoII atoms, and each of them is six-coordinated with distorted octahedral geometry. The six atoms coordinated to the Co1 center come from two nitrogen atoms of two bpa ligands and two oxygen atoms from a bta ligand as well as two water molecules. The Co2 ion is coordinated by three carboxylate oxygen atoms from two bta ligands, one pyridyl nitrogen atom from a bpa ligand and two water molecules. The six donors coordinated to the Co3 ion come from two nitrogen atoms of two bpa ligands and four oxygen atoms from two bta ligands. The axial sites O7Co1O8, O10Co2N3, and O11Co3N4 with angles of 165.83, 172.11, and 146.92°, respectively, indicate a much too distorted octahedral geometry for Co3 (see Figure S1, Supporting Information). The three carboxylates of bta ligands in motif A are chelating, uncoordinated, and chelating, respectively, binding to two Co3 centers, while those in motif B show chelatingchelatingunidentate coordination modes, linking to one Co1 and two Co2 ions. The structure of motif A is easily to understand, in which the bridging bta and bpa (twisted bridging) ligands connect the Co3 atoms to result in a puckered 2D (4,4) net viewed along the a axis. However, for motif B, the structure seems very complicated and is described in detail below. The linkage of the bta anions (using 1- and 3-carboxylate groups), bpa (linear bridging), and the Co2 centers affords a (6,3) layer parallel to the bc plane (see Figure 1c), and three identical such (6,3) layers are interlocked with each other, affording a 3-fold interpenetrated 2D net. Interestingly, the (6,3) networks are further joined together by the semicircle Co1bpa chains via the 2-carboxylate groups of bta that are bound to Co1 atoms, leading to the formation of a unique 2D self-penetrating motif B along the b axis (see Figure 1d). From the viewpoint of network topology, in motif
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Figure 2. Schematic representation of the polycatenane architecture formed by two motif A and one motif B in 1.
B, all the CoII centers and bta ligands can be regarded as the 3-connected nodes to afford a trinodal net with the Schl€afli symbol of (102.11)(103)(103), which represents a new 3-connected layered coordination network. The extended vertex symbols for Co1, Co2, and bta are (102.102.112), (10.10.103), and (102.102.102), respectively. Remarkably, the overall supramolecular architecture of complex 1 is formed by two motif A plus one motif B in a polycatenated arrangement, showing a unique 2D (selfpenetrating) + 2D (4,4) f 2D (interpenetrating) structural prototype (see Figure 2). It can be properly portrayed as a “sandwich”, and motif B is positioned between two motif A. However, they are not isolated, but the twisted bpa rods of motif A lock the semicircle Co1bpp chains of motif B, which is situated at the upper and lower layers. Very recently, an entangled system with both self-penetrating and interpenetrating structural features has been reported by Zhang and Du et al.,5 in which the interpenetration is originated from the two identical 3D self-penetrating nets. And also, several intriguing 2D f 2D parallel interpenetrating structures have been reported. For example, four mixed-ligand coordination polymers showing both polyrotaxane and polycatenane characters were reported by Su et al.,11 in which the elements of the penetration are unanimous (4,4)-, (6,3)-, and (3,6)-connected layers. In the report of Champness,12 an interwoven bilayer with one-dimensional (1D) double helical channels is built from a parallel 2D f 2D interpenetration. Differently, complex 1 described herein represents the first example of an entangling system arising from interpenetration of different topological components in the same crystal, one of which is a self-interpenetrating motif. The ZnII species 2 with the same organic tectons, however, shows a distinct 3D network with a new topology. The asymmetric unit contains two crystallographically independent but similar ZnII centers. If we consider the weak Zn1O6A (2.551(3) Å; symmetry codes: A, x, y, z) and Zn2O1B (2.507(3) Å; symmetry codes: B, x + 1/2, y 1/2, z + 1/2) bond, each one is five-coordinated and exhibits distorted squarepyramidal geometry (see Figure S2, Supporting Information). Different from 1, the three carboxylate groups of bta ligands in 2 show the unidentate-μ2(O,O0 )-unidentate fashion to coordinate to two Zn1 and two Zn2 ions. In this way, the ZnII centers are connected by the μ3-bta ligands to afford a 2D helical doublelayer (see Figure 3a and Figure S3, Supporting Information), where the carboxylate groups of O1C7O2 and O3C8 O4 connect the adjacent ZnII atoms to generate the right- and 3310
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Figure 3. Views of 2. (a) 2D helical double-layer array along the bc plane. (b) Schematic representation of the 4-connected topological net (green balls for Zn1, blue balls for Zn2, and purple balls for bta).
left-handed helices with a pitch of 10.963 Å. Furthermore, these 2D patterns are pillared by the bpa bridges to afford a complicated 3-D polymeric framework. From the topological view, each Zn1, Zn2, and bta building unit can be similarly considered as the 4-connected nodes, and thus, the final 3D network has a new trinodal 4-connected topological framework (see Figure 3b) with the Schl€afli symbol of (3.4.5.6.7.8)(3.6.7.103)(3.4.5.103). As an asymmetric organic linker, the benzene-1,2,3-tricarboxylic acid ligand possesses special orientations, strong steric hindrance of its three carboxylate groups, and the multiplicity of the dihedral angles between the plane of the carboxylate groups and the phenyl ring plane. The carboxyl groups of H3btb can rotate to satisfy the space requirement, and the constructed MOFs can extend by forming short bridges via one carboxylic end or long bridges via a benzene ring to form high asymmetric molecules or supramolecules.13 By using the benzene-1,2,3tricarboxylic acid ligand, two new CoII complexes based on Δ-chains have been reported by Wood et al.13a Recently, Chen et al.13f have successfully isolated nine new compounds via the in situ metalligand hydrothermal reaction of benzene-1,2,3tricarboxylic acid. The resultant products show versatile structures and magnetic properties. Liu and co-workers13k reported a series of ZnII complexes based on 1,2,3-benzenetricarboxylate and different auxiliary N-donor ligands, which display various 1D to 3D topological networks and diverse luminescent properties. These results as well as our research demonstrates that benzene1,2,3-tricarboxylic acid could be a potential building block to construct novel coordination polymers with unusual architectures and interesting physical properties. The magnetic properties of 1 were measured in the 2300 K temperature range in a field of 2 KOe on a MPMS-7 SQUID magnetometer and shown as χMT and χM versus T plots (see Figure S4, Supporting Information). Diamagnetic corrections were made with Pascal’s constants for all constituent atoms. The magnetic properties of 1 were measured in the 2300 K temperature range and shown as χMT and χM versus T plots (see Figure S4, Supporting Information). The experimental χMT value at 300 K is 2.67 cm3 K mol1, which is slightly larger than
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the spin-only value (1.875 cm3 K mol1 with g = 2.0) expected for the uncoupled CoII ion. This is due to the occurrence of an unquenched orbital contribution typical of the 4T1g ground state in six-coordinated CoII complexes.14 As the temperature decreases, the χMT value decreases, indicating the presence of antiferromagnetic interactions. Upon cooling, the χMT values continuously decrease to 1.26 cm3 K mol1 at 2 K. In fact, as described above, the Co 3 3 3 Co distances in complex 1 are 5.9, 6.7, 13.6 Å, respectively. As a consequence of these structural features, the possible magnetic pathways in 1 are almost nonexistent. The observed decrease of χMT at lower temperature may be attributed to the thermal depopulation of the excited Kramer’s doublets originated by spinorbit and low symmetry splitting of 4T1g of the CoII ion. The emission spectrum of complex 2 was recorded in the solid state at room temperature (see Figure S5, Supporting Information). Upon excitation at ca. 324 nm, complex 2 exhibits the fluorescence emission band at ca. 422 nm. Since the ZnII ions are difficult to oxidize or reduce, this band should be assigned to the intraligand fluorescent emissions that are tuned by the metalligand interactions and deprotonated effect of the tricarboxyl ligand.15 Phase purities of the bulk materials of 1 and 2 were confirmed by X-ray powder diffraction (XRPD) patterns (see Figure S6, Supporting Information). Complexes 1 and 2 are air stable and retain the crystalline integrity at ambient conditions. The thermal behavior show that there is no mass loss for 1 and 2 until ca. 140 and 300 °C, respectively. After that, the weight loss occurs upon heating, which suggests the decomposition of the crystalline material (see Figure S7, Supporting Information). In summary, two interesting coordination frameworks, including a new type of entangled system 1 consisting of distinct selfinterpenetrated and (4,4) layered motifs interpenetrated within the same crystalline lattice and a 3D polymeric species 2 with unique 4-connected network topology, have been successfully assembled. Obviously, the different organization of the whole supramolecular patterns of such two MOFs is only controlled by the nature of metal centers. To the best of our knowledge, 1 and 2 are the first supramolecular architectures with unprecedented net topologies. These results not only provide two intriguing structural examples of MOFs but also confirm the significant potential of the unsymmetric tricarboxyl tectons for the construction of entangled frameworks, which is further ongoing in our lab.
’ ASSOCIATED CONTENT
bS
Supporting Information. Crystallographic data in CIF format, additional structural illustrations, additional structural illustration of 2, temperature dependence of χMT and χM plot for 1 and solid-state emission spectrum of 2, PXRD patterns, TGA curves for complexes 1 and 2. This material is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected] (L.-Y.W.);
[email protected] (M.D.).
’ ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (21073082 and 21071074), 2009GGJS104 and sponsored by Program for Science & Technology 3311
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Crystal Growth & Design Innovation Talents in Universities of Henan Province (2011HASTIT027). M.D. also acknowledges the support from Tianjin Normal University.
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816 m, 712 m. Preparation of [Zn2(bta)(OH)(bpa)]n (2). Complex 2 was synthesized in a similar way as that for 1, except that Co(OAc)2 3 4H2O was replaced by Zn(OAc)2 3 2H2O. Yield: 39% (10.51 mg, based on Zn). Elemental analysis (%) for C21H16N2O7Zn2: calcd, C 46.79, H 2.99, N 5.20; found, C 46.89, H 2.92, N 5.13. IR (cm1): 3438 m, 2918 m, 1619s, 1548 m, 1371 m, 1108 m, 1015 m, 981 m, 724 m. (10) Crystal data for 1: C48H45Co3N5O16.5 (Mr = 1132.68), monoclinic, C2/c, a = 49.052(6), b = 9.5736(11), c = 20.209(2) Å, β = 103.2440(10)°, V = 9237.8(18) Å3, Z = 4, F = 1.629 g cm3, S = 1.024, R = 0.0349 and wR = 0.0803. Crystal data for 2: C21H16N2O7Zn2 (Mr = 539.10), monoclinic, P21/n, a = 9.8885(11), b = 10.9627(12), c = 17.946(2) Å, β = 91.2710(10)°, V = 1945.0(4) Å3, Z = 4, F = 1.841 g cm3, S = 1.031, R = 0.0356 and wR = 0.0801. CCDC-793955 for 1 and 773883 for 2 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/ cif. (11) Lan, Y. Q.; Li, S. L.; Qin, J. S.; Du, D. Y.; Wang, X. L.; Su, Z. M.; Fu, Q. Inorg. Chem. 2008, 47, 10600. (12) Yang, W.; Lin, X.; Blake, A. J.; Wilson, C.; Hubberstey, P.; Champness, N. R.; Schr€oder, M. Inorg. Chem. 2009, 48, 11067. (13) (a) Gutschke, S. O. H.; Price, D. J.; Powell, A. K.; Wood, P. T. Angew. Chem., Int. Ed. 2001, 40, 1920. (b) Dale, S. H.; Elsegood, M. R. J.; Coombs, A. E. L. CrystEngComm 2004, 6, 328. (c) Guo, F.; Harris, K. D. M. J. Am. Chem. Soc. 2005, 127, 7314. (d) Liu, B.; Xu, L. Inorg. Chem. Commun. 2006, 9, 364. (e) Liu, Y.-Y.; Ma, J.-C.; Xie, Y.-P.; Ma, J.-F. J. Coord. Chem. 2008, 61, 3450. (f) Zheng, Y.-Z.; Zhang, Y.-B.; Tong, M.-L.; Xue, W.; Chen, X.-M. Dalton Trans. 2009, 1396. (g) Zhang, Z.-J.; Liu, H.-Y.; Zhang, S.-Y.; Shi, Wei.; Cheng, P. Inorg. Chem. Commun. 2009, 12, 223. (h) Akhbari, K.; Morsali, A. Inorg. Chem Acta. 2009, 362, 1692. (i) Liu, G.-X.; Zhu, K.; Nishihara, S.; Huang, R.-Y.; Ren, X.-M. Inorg. Chem Acta. 2009, 362, 5103. (j) Zhang, X.-C.; Xu, L.; Liu, W.-G.; Liu, B. Bull. Korean Chem. Soc. 2010, 9, 2598. (k) Liu, W.; Yu, J.; Jiang, J.; Yuan, L.; Xu, B.; Liu, Q.; Qu, B.; Zhang, G.; Yan, C. CrystEngComm 2011, 13, 2764. (14) (a) Carlin, R. L. Magnetochemistry; Springer-Verlag: Berlin, Heidelberg, 1986. (b) Mabbs, F. E.; Machin, D. J. Magnetism and Transition Metal Complexes; Chapman and Hall Ltd.: London, 1973. (15) (a) Wen, L. L.; Dang, D. B.; Duan, C. Y.; Li, Y. Z.; Tian, Z. F.; Meng, Q. J. Inorg. Chem. 2005, 44, 7161. (b) Hu, T. L.; Zou, R. Q.; Li, J. R.; Bu, X. H. Dalton Trans. 2008, 1302.
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