Two cobalt(II) coordination polymers [Co2(H2O)4(Hbidc)2]n and [Co(Hbidc)]n (Hbidc = 1H-benzimidazole-5,6-dicarboxylate): syntheses, crystal structures, and magnetic properties

Abstract

Two novel cobalt(II) coordination polymers [Co₂(H₂O)₄(Hbidc)₂]_n (1) and [Co(Hbidc)]_n (2), (Hbidc = 1H-benzimidazole-5,6-dicarboxylate) were synthesized hydrothermally by treating CoSO₄ and H₃bidc at 160 or 220 °C, respectively. X-Ray diffraction analyses showed that compound 1 is a 1-D chain polymer with dimer units [Co₂(H₂O)₄(Hbidc)₂] and the infinite chains of compound 1 array uniformly towards the crystallographic a-axis in a 3-D supramolecular framework which possesses abundant hydrogen-bonding interactions between uncoordinated carboxylo-oxygen atoms and coordinated water molecules or N–H groups in imidazole rings. Compound 2 is a novel five-coordinated cobalt(II) chain compound exhibiting a 2-D polymeric network with parallel zip-like cobalt–carboxylate chains along the crystallographic b-axis and the 2-D polymeric networks of compound 2 exhibit a layered arrangement, in which the strong hydrogen-bonding interaction between uncoordinated carboxylo-oxygen atoms and N–H groups in the imidazole rings play a key role in the final 3-D supramolecular architectures. Magnetic studies revealed that compound 1 shows a ferromagnetic coupling between two Co^II ions in the dimer unit and compound 2 exhibits an antiferromagnetic property.