Inorganic Chemistry Communications 14 (2011) 228–230

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Inorganic Chemistry Communications

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Rare 5-connected BN topology in homochiral Cd(II) camphoratewith 2-(4-pyridyl)benzimidazole

Fei Li a,b, Yao Kang a, Yu-Mei Dai b,⁎, Jian Zhang a,⁎a State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, the Chinese Academy of Sciences, Fuzhou, Fujian 350002, Chinab College of Chemistry & Material Science, Fujian Normal University, Fuzhou, Fujian 350007, China

⁎ Corresponding authors.E-mail address: zhj@fjirsm.ac.cn (J. Zhang).

1387-7003/$ – see front matter © 2010 Elsevier B.V. Adoi:10.1016/j.inoche.2010.10.029

a b s t r a c t

a r t i c l e i n f o

Article history:Received 10 September 2010Accepted 26 October 2010Available online 30 October 2010

Keywords:Crystal structureCadmiumHydrogen bondTopologyHomochiral

Presented here is a new photoluminescent homochiral Cd(II) camphorate with auxiliary 2-(4-pyridyl)benzimidazole ligand, which is the first homochiral metal-organic framework adopting the 5-connectedBN topology.

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© 2010 Elsevier B.V. All rights reserved.

Homochiral metal-organic framework materials (MOFs) haveattracted more and more attention in recent years not only for theirpotential applications on enantioselective catalysis, separation and soforth, but also for fascinating architectures and topologies [1,2]. Onecommon strategy for the design of homochiral functional frameworkmaterials is the incorporation of enantiopure organic ligands thatact as cross-linking or pendent building units. For example, a variety ofhomochiral MOFs based on enantiopure D-(+)-camphoric acid(D-H2cam) with different transition metals have been successfullyreported by Bu et al. [3,4]. Although several metal camphorates withdifferent auxiliary pyridyl ligands have been reported, another rigidN-donor spacer, such as 2-(4pyridyl)benzimidazole (= 4-PyBIm), hasnever been known in anymetal camphorate systems. The incorporationof 4-PyBImwith extended π systemmay help to create new homochiralmaterials with enhanced photoluminescent properties. Furthermore,unlike other neutral linear imine ligands (4,4′-bipyridine, trans-1,2-bis(4-pyridyl)-ethylene, and 4,4′-trimethylenedipyridine), the4-PyBIm ligand has three possible N donors and often exhibits distinctcoordination and supramolecular chemistry [5]. Thus, different struc-tural topologies may be generated from this combination strategy. Inthiswork,we report a newhomochiral Cd(II) camphoratewith4-PyBImas the auxiliary ligand, namely [Cd(D-cam)(4-PyBIm)]n (1), whichhas rare 5-connected BN topology and exhibits interesting photolumi-nescent property.

The colorless crystals of 1were hydrothermally synthesized in 80%yield by reacting Cd(NO3)2•4H2O with 4-PyBIm and D-H2cam in thepresence of sodium carbonate at 160 °C [6]. The structure of 1 wasidentified by satisfactory elemental analysis, single crystal andpowder X-ray diffraction [7]. Singe-crystal X-ray diffraction revealsthat 1 crystallizes in monoclinic chiral space group P21.

The asymmetric unit of 1 contains two Cd2+ cations, two depro-tonated D-cam ligands and two neutral 4-PyBIm ligands (Fig. 1a).Both Cd2+ cations exhibit similar distorted octahedral configuration,each is coordinated by two nitrogen atom respectively from theimidazole ring and the pyridyl ring of two 4-PyBIm ligands, and fouroxygen atoms from two bis-(bidengtate) D-cam ligands. The D-camligands link the octahedral Cd centers into a zigzag chain along theb axis. The 4-PyBIm ligand is not deprotonated and acts as a T-shapedlinker. Two 4-PyBIm ligands doubly bridge two independent Cdcenters via the coordination of two pyridyl N donors and twoimidazolate N donors, which also connect the Cd(D-cam) chains into ahoneycomb-like layer with topological representation of 63 (Fig. 1b).This layer consists of 6-membered rings with a size of 12.1×21.2 Å2.

Interestingly, the uncoordinated but protonated imidazolate Ndonor of the 4-PyBIm ligand forms strong hydrogen bond with thecarboxylate O acceptor from the adjacent layer (Fig. 1c). The N-H…Odistances are 2.748 Å and 2.727 Å, respectively, indicating the stronghydrogen bonding interactions. So the resulting layers are furtherstacked up along the a axis through such strong hydrogen bondingconnectivity, creating the final three-dimensional framework. Byconsidering the coordination and hydrogen bonds, the 3-D frameworkcan be simplified as a 5-connected BN (or bnn) net [Schläfli symbol

Fig. 2. (a) Experimental and simulated X-ray powder diffraction patterns of compound1; (b) Thermo-gravimetric diagram of compound 1.

Fig. 1. (a) The molecular structure of 1; (b) the 63 layer in 1; (c) the hydrogen bondinginteractions (dashed lines) between the layers; (d) schematic representation of the5-connected BN topology.

229F. Li et al. / Inorganic Chemistry Communications 14 (2011) 228–230

(46)(64)] with each Cd center being 5-connected trigonal bipyramidalnode (Fig. 1d) [8]. Several BN-type frameworks have been knownbefore[9], but none of them involve both covalent and strong hydrogen bondsand exhibit homochiral features.

The phase purity of the crystalline sample of 1 was characterizedby powder X-ray diffraction (Fig. 2a). Thermo-gravimetric analysis(TGA) was performed at a heating rate of 10 °C min−1 on crystallinesample of 1 in N2 at the flow rate of 50 mL min−1. There is almost noweight loss before 416 °C. After that, the onset decomposition tookplace (Fig. 2b).

In the solid states, compound 1 exhibits photoluminescence under365 nm light excitation. It gave strong emission peak maximum at404 nm at room temperature (Fig. 3). It has been reported thatorganic compound 4-PyHBIm has weak emission band centered at492 nm [5b]. Most of the Cd(II)-cyanide complexes exhibit lumines-cence in the range 400–500 nm [10]. So the photoluminescence of 1may be assigned to MLCT [11].

In summary, we presented here a new photoluminescent homo-chiral Cd(II) camphorate with auxiliary 2-(4-pyridyl)benzimidazoleligand. To our knowledge, it is the first homochiral metal-organicframework adopting the 5-connected BN topology. The results revealthat the attendance of different auxiliary ligands can largely modifythe metal camphorate architectures.

Fig. 3. Solid-state emission spectra for compound 1 at room temperature.

Acknowledgments

This work was supported by the 973 program (2011CB932504)and NSFC (21073191).

Appendix A. Supplementary data

Supplementary data to this article can be found online atdoi:10.1016/j.inoche.2010.10.029.

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