Synthesis and characterization of Cu(II), Co(II) and Ni(II) coordination polymers containing bis(imidazolyl) ligands

Abstract

Two structurally related flexible imidazolyl ligands, bis( N-imidazolyl)methane (L 1) and 1,4-bis( N-imidazolyl)butane (L 2), were reacted with Cu(II), Co(II) and Ni(II) salts of aliphatic/aromatic dicarboxylic acids resulting in the formation of a number of novel metal–organic coordination architectures, [CuB 2(ox) 2(L 1) 2(H 2O) 2] · 4H 2O ( 1) (ox = oxalate), [Cu(pdc)(L 2) 1.5] · 4H 2O ( 2, pdc = pyridine-2,6-dicarboxylate), [Co(L) 2(H 2O) 2](tp) · 4H 2O ( 3, tp = terephthalate), [Ni(L 1) 2(H 2O) 2](ip) · 5H 2O ( 4, ip = isophthalate), [Cu 2(L 1) 4(H 2O) 4](tp) 2 · 7H 2O ( 5), [Co(mal)(L 1)(H 2O)] · 0.5MeOH ( 6, mal = malonate), [Co(pdc)(L 1)(H 2O)] ( 7). All the complexes have been structurally characterized by X-ray diffraction analysis. The different coordination modes of the dicarboxylate anions, due to their chain length, rigidity and diimidazolyl functionality, lead to a wide range of different coordination structures. The coordination polymers exhibit 1D single chain, ladder, 2D sheet and 2D network structures. The aliphatic and aromatic dicarboxylates can adopt chelating μ 2 and chelating-bridging μ 3 coordination modes, or act as uncoordinated counter anions. The central metal ions are coordinated in N 2O 4, N 4O 2, N 2O 3 and N 3O 3 fashions, depending on the ancillary ligands. The topology of 1 gives rise to macrocycles which are connected through hydrogen bonds to form 1D chains, whereas compound 2 exhibits a 1D polymeric ladder in which the carboxylate acts as a pincer ligand. Compounds 3– 5 show doubly bridged 1D chains, and the dicarboxylate groups are not coordinated but form 2D corrugated sheets with water molecules intercalated between the cationic layers. Compound 6 has a 2D network sheet structure in which each metal ion links three neighboring Co atoms by the bis( N-imidazolyl)methane ligand. The cobalt compound 7, with a 2D polymeric double sheet structure, is built from pincer carboxylate (pdc) and 1,4-bis( N-imidazolyl)methane ligands.