Structural versatility of six transition metal complexes based on M(II)(2,2′-biimidazole) building blocks and co-ligands

Abstract

Reaction of transition metal(II) salts with 2,2′-biimidazole (H2biim) and co-ligands formed a series of new complexes, [M(H2biim)2(bipy)2](NO3)2·2H2O (1–3) (M=Co, Ni, Zn), [Co(H2biim)2(bipy)](ClO4)2·3H2O (4), {[Cu(H2biim)2]3(μ-C3H3O4)2 (C3H2O4)2}·6H2O (5), [Co(H2biim)2(H2O)2](C3H3O4)2 (6) (bipy=4,4′-bipyridine, C3H2O4=malonate dianion, C3H3O4=malonate anion). These complexes were characterized by single-crystal X-ray diffraction, and elemental analysis. All complexes except 4 were also characterized by luminescence spectra and thermogravimetric analysis. The crystal packing of these six complexes shows that cationic M(II)(2,2′-biimidazole) fragments are self-assembled to construct the 3D supramolecular networks by hydrogen bonding and π–π interactions. The 3D supramolecular networks are significantly affected by counter anion and co-ligands. In complexes 1–3, there are two sets of (4,4) nets which pass through each other to form inclined 2D interpenetration. Complex 4 is obtained by similar reactions as 1 Compared with 1, the only difference in 4 with the reactant Co(NO3)2·6H2O replaced by Co(ClO4)2·6H2O, but it has a very different structure. In 4, the 3D networks containing cavities of 23×23Å is formed. In complex 5, the uncoordinated waters form an infinite 1D pipe structure which is embedded in the 3D porous network. The acid–water ring and R22(9) synthons in complex 6 lead to the formation of (4,4) 2D network.