Syntheses and structures of two one-dimensional double-stranded lead polymers of dicyanamide with unusual coordination mode
Two novel lead coordination polymers Pb(dca)(NO3)(1,10-phen) (1) and Pb(dca)2(2,2′-bipy)(H2O) (2) have novel one-dimensional double-stranded chains with dca in a novel 1,1,5-μ3-coordination mode.
Introduction
Coordination polymers constitute one of the most important class of organic–inorganic hybrid materials which have attracted great research interests [1], [1](a), [1](b), [2], [2](a), [2](b). Our interest in this field has focused on the construction of novel PbX2-based organic–inorganic hybrids using lead(II) ion as the building block due to the belief that its versatile coordination number and varied coordination geometries would give rise to novel coordination polymeric networks [3], [3](a), [3](b), [3](c), [3](d), [3](e), [3](f), [3](g), [3](h), [3](i), [3](j). PbX2-based coordination polymers with nitrogen-containing Lewis bases such as 2,2′-bipyridine, 4,4-bipyridine have been studied and found to exhibit one- or two-dimensional structures [3], [3](a), [3](b), [3](c), [3](d), [3](e), [3](f), [3](g), [3](h), [3](i), [3](j), where PbX2 chain or layer perseveres. Furthermore, coordination polymers based on lead pseudohalide Pb(SCN)2 have also been prepared and structurally characterized [3](a), [4].
The coordination chemistry of the pseudohalide ligand dicyanamide(dca) has been explored for many years. Köhler [5], [5](a), [5](b), [5](c), [5](d), [5](e), [5](f), [5](g), Hvastijova [6], [6](a), [6](b), [6](c), [6](d) and their co-workers have published a series of papers describing transition metal complexes with dca, but without X-ray single crystal structures. Transition metal compounds with dca have recently received renewed interest initiated by the novel magnetic properties of binary complexes M(dca)2 (M=Cr, Mn, Fe, Co, Ni, Cu) [7], [7](a), [7](b), [7](c), [7](d). Many coordination polymers of transition metals of dca with nitrogen-containing coligands such as 2,2′-bipyridine, 4,4-bipridine and pyrazine have subsequently appeared in the literatures [8], [8](a), [8](b), [8](c), [8](d), [8](e), [8](f), [8](g), [8](h). However, the coordination chemistry of main group elements of dca is scarcely reported [9], [10], [10](a), [10](b), [10](c), [11], [15], [16], [17]. Pb(dca)2 was prepared in 1922, but its structural characterization was not given [9]. More recently, we [16] and Schnick et al. [17] have independently determined the crystal structure of Pb(dca)2, which is isotypic with Ba(dca)2 [17]. From the viewpoint of the crystal engineering of supramolecular coordination network, it is the first novel (4,5,9)-connected 3D polymeric network [16].
Five coordination modes of I–V of dca have been substantiated by X-ray crystallography (Scheme 1). The most common coordination mode is 1,5-μ2 bridging, II, which has been found in many transition metal compounds and some main group metal compounds. The terminal coordination mode I occurs in some mononuclear complexes for example [Cu(1,10-phen)2(dca)2] [12], [CuII(1,10-phen)2{dca}2][C(CN)3] [13] and Mn(NITpPy)2(dca)2(H2O)2 [14]. The three-coordinate mode III is observed in the rutile-like material M(dca)2, M=Cr, Mn, Fe, Co, Ni. The unusual coordination mode IV is observed in (CH3)2Tl(dca) [15] and Pb(dca)2 [16], [17]. Five-connecting coordination mode V was newly found in Pb(dca)2 16[17]. The possible two-connecting mode VI has yet to be confirmed, although it is postulated for one isomer of [CuII(dca)2(imidazole)] [6b].
Following our research on PbX2-based organic-inorganic hybrids [3](h), [3](i), [3](j), [16], we combined dca and 1,10-phenanthroline or 2,2-bipyridine with the expectation that novel polymeric structure and even new coordination mode of dca would be found by extending from halide to pseudohalide, taking advantage of the versatibility of both lead and dca in coordination chemistry. Here we report two one-dimensional coordination polymers Pb(dca)(NO3)(1,10-phen) (1) and Pb(dca)2(2,2′-bipy)(H2O) (2) displaying a new three-connecting coordination mode VII which has not been observed before.
Section snippets
Experimental
All chemicals were used as received without further purification. Elemental analyses were carried out on a Perkin–Elmer 240C elemental analyzer. IR spectra were recorded on a Perkin–Elmer 1600 FT-IR spectrometer as KBr pellets in the 4000 to ∼400 cm−1 range.
Results and discussions
The coordination environment of Pb(II) in Pb(dca)(NO3)(phen) (1) is shown in Fig. 1. Each lead atom is seven-coordinated with two oxygen atoms from NO3 − group, two nitrogen atoms from 1,10-phen, and three nitrogen atoms from bridging dca ligands. The coordination geometry is far from regular. The structure consists of a one-dimensional chain bridged by dca ligands in 1,1,5-μ3 coordination mode, VII, which has not been observed in the literature. The pairwise bridging between adjacent chains
Supplementary material
Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC Nos. 188823 and 188824 for compounds 1 and 2, respectively. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: +44-1223-336033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk).
Acknowledgements
This work was supported by a Major State Basic Research Development Program (grant no. G2000077500), an Overseas Outstanding Young Scholar Fund from the National Natural Science Foundation of China (no. 20028101) and a Natural Science Grant of Jiangsu Province (BK 99032) and the support from the Analytic Center of Nanjing University.
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Permanent address: Department of Chemistry, Nantong Teacher's College, Nantong 226007 P.R. China