Received 18 April 2011
Poly[aqua[2-1,4-bis(imidazol-1-ylmethyl)benzene-2N3:N3'](2-5-hydroxybenzene-1,3-dicarboxylato-4O1,O1':O3,O3')cadmium(II)], a twofold interpenetrated CdSO4-like metal-organic polymer
In the title cadmium(II) complex, [Cd(C8H4O5)(C14H14N4)(H2O)]n, the 5-hydroxybenzene-1,3-dicarboxylate (5-OH-1,3-bdc) and 1,4-bis(imidazol-1-ylmethyl)benzene (1,4,-bix) ligands bridge water-coordinated CdII atoms to generate a three-dimensional network. Two carboxylate groups from different ligands function as O,O'-chelates, while two imidazole N atoms from different ligands coordinate in a monodentate fashion, and one water molecule completes the seven-coordinate pentagonal bipyramid around the CdII atom, in which the N atoms occupy the axial sites and the O atoms occupy the equatorial sites. The overall architecture is a twofold interpenetrated CdSO4-type framework. The two crystallographically equivalent frameworks are linked by O-HO hydrogen bonds between the water, hydroxy and carboxylate groups.
The design and synthesis of metal-organic frameworks (MOFs) has been an area of rapid growth in recent years owing to the potential applications of MOFs in nonlinear optics, luminescence, magnetism, catalysis, gas absorption, ion exchange and as zeolite-like materials for molecular selection (O'Keeffe et al., 2008). Structural diversity in MOFs can occur as a result of various processes, including supramolecular isomerism, interpenetration or interweaving (Batten & Robson, 1998; Batten, 2001). Ideally, the topologies of MOFs can be controlled and modified by the coordination geometry preferred by the metal ion and the chemical structure of the organic ligand chosen (Abrahams et al., 1999; Yang et al., 2008). In this regard, rigid N-donor 4,4'-bipyridine (bipy) and its derivatives have been studied in the construction of MOFs (Qiao et al., 2008). So far, a number of MOFs based on bipy and its derivatives have been reported, including one-dimensional chains, two-dimensional layers and three-dimensional frameworks (Carlucci et al., 2003). However, reports of MOFs constructed by flexible N-donor ligands are relatively rare (Wang et al., 2006). Among such ligands, bis(imidazole) derivatives are a good choice (Yang et al., 2008), leading to some intriguing interpenetrating architectures and topologies (Wang et al., 2006). In this work, we chose 5-hydroxybenzene-1,3-dicarboxylic acid (5-OH-1,3-H2bdc) as a dicarboxylate ligand and 1,4-bis(imidazol-1-ylmethyl)benzene (1,4-bix) as a flexible N-donor ligand, yielding a new coordination polymer, [Cd(5-OH-1,3-bdc)(1,4-bix)(H2O)], (I), with a fascinating twofold interpenetrated three-dimensional CdSO4-like framework. After the acceptance of this paper, we noticed that the structure of (I) has recently been described by Xia et al. (2011). However, the interpenetrated topology and hydrogen-bonding interactions were not well discussed in that report.
The asymmetric unit of (I) contains one CdII atom, one 5-OH-1,3-bdc anion, one 1,4-bix ligand and one coordination water molecule (Fig. 1). Each CdII atom is seven-coordinated in a pentagonal bipyramid by four carboxylate O atoms from two different 5-OH-1,3-bdc anions, one water O atom and two N atoms from two distinct 1,4-bix ligands. The N atoms occupy the axial sites and the O atoms occupy the equatorial sites of the bipyramid. The Cd-Ocarboxylate distances (Table 1) are comparable to those observed in [Cd(1,4-bdc)(bpdo)(H2O)]n (1,4-bdc is benzene-1,4-dicarboxylate and bpdo is 4,4'-bipyridine N,N'-dioxide; Xu & Xie, 2010).
Each crystallographically unique CdII atom is bridged by the 1,4-bix ligands and 5-OH-1,3-bdc anions to generate a novel three-dimensional framework (Fig. 2). The CdCd distances bridged by 1,4-bix and 5-OH-1,3-bdc are 14.3668 (12) and 9.8433 (8) Å, respectively. Topologically, the CdII centre is defined as a four-connected node, and 1,4-bix and the 5-OH-1,3-bdc serve as linkers. Therefore, on the basis of the concept of chemical topology, the overall structure of (I) is a four-connected framework with the Schläfli symbol of 658. Topological analysis reveals that this three-dimensional framework is a typical CdSO4 net. Interestingly, the large spaces in the single three-dimensional framework allow another identical framework to interpenetrate it, providing a twofold interpenetrating CdSO4 framework (Fig. 3). Each CdSO4 net is hydrogen bonded to its neighbour through O-HO hydrogen bonds among the water molecules, hydroxy group and carboxylate O atoms (Table 2).
So far, some related interpenetrated CdSO4-like MOFs based on both dicarboxylate and flexible N-donor bridging ligands have been reported. The structure of [Zn2(1,4-bdc)Cl2(bpp)]n [1,4-bdc is benzene-1,4-dicarboxylate and bpp is 1,3-bis(4-pyridyl)propane; Zhang et al., 2006] also contains two crystallographically equivalent nets, but differs from (I) in that the four-connected nodes are based on ZnII dimers rather than mononuclear complexes. [Zn(mip)(bpa)]n [mip is 5-methylisophthalate and bpa is 1,2-bis(4-pyridyl)ethane; Ma et al., 2009] shows an unusual threefold interpenetrated CdSO4 topology. [Ni(oba)(bbi)]2·H2O [oba is 4,4'-oxybis(benzoate) and bbi is 1,1'-(1,4-butanediyl)bis(imidazole); Yang et al., 2009] also shows twofold interpenetrated nets as in (I); however, the nets are crystallographically distinct.
| || Figure 1 |
A view of the local coordination of the CdII atom in (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. [Symmetry codes: (i) x, y + 1, z - 1; (ii) x + , -y + 1, z - .]
| || Figure 2 |
A view of a single CdSO4 net of (I), showing bridging by 1,4-bix and 5-OH-1,3-bdc ligands.
| || Figure 3 |
A view of the twofold interpenetrating three-dimensional CdSO4 net of (I).
A mixture of CdCl2·2.5H2O (0.5 mmol), 1,4-bis(imidazol-1-ylmethyl)benzene (0.5 mmol), 5-hydroxybenzene-1,3-dicarboxylic acid (0.5 mmol) and water (12 ml) was sealed in a 23 ml Teflon-lined stainless steel Parr bomb. The bomb was heated at 413 K for 3 d and then cooled to room temperature. Colourless block-shaped crystals were collected and washed with water; the yield based on Cd was about 40%.
Carbon-bound H atoms were positioned geometrically [C-H = 0.93 (aromatic) or 0.97 Å (methylene)] and included as riding atoms, with Uiso(H) values fixed at 1.2Ueq(C). H atoms of water molecules were located in difference Fourier maps and refined isotropically with distance restraints of O-H = 0.85 (1) Å and HH = 1.35 (1) Å, and with Uiso(H) = 1.5Ueq(O). The hydroxy H atom was located in a difference Fourier map and refined isotropically with a distance restraint of O-H = 0.82 (1) Å and with Uiso(H) = 1.5Ueq(O).
Data collection: SMART (Bruker, 1997); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL-Plus (Sheldrick, 2008); software used to prepare material for publication: publCIF (Westrip, 2010).
Supplementary data for this paper are available from the IUCr electronic archives (Reference: SQ3290 ). Services for accessing these data are described at the back of the journal.
We thank Jilin Normal University and the University of Malaya for supporting this study.
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