Sulfate-Incorporated Co(II) Coordination Frameworks with Bis-imidazole Bridging Ligands Constructed by Covalent and Noncovalent Interactions

Abstract

Three 3D supramolecular networks, [Co(H(2)L1)(2)]center dot (SO4)center dot 2H(2)O (1), [Co(H(2)L1)(SO4)(H2O)(DMF)] (2), and [Co(H(2)L2)(SO4)(H2O)] (3), were prepared by reacting Co(II) sulfate with the rigid bis-imidazoles of 1,4-di(1H-imidazol-4-yl)benzene (H(2)L1) and 1,3-di(1H-imidazol-4-yl)benzene (H(2)L2) in solvothermal conditions. Compounds 1 and 2 containing the H(2)L1 ligand were isolated under different solvent-pair ratios. The structure of 1 can be described as a 6-fold interpenetrating 3D dia net in which the sulfate anions are positioned in the void spaces to balance the overall charge of the framework In comparison, complex 2 shows a rectangular 2D grid consisting of 1D sulfate-bridged chains linked by H(2)L1. When H(2)L2 is used in the reaction, the complex 3 having a 3D interdigitaed network with helical chains is formed, which is the first example of an H(2)L2-connected coordination polymer. The sulfate ions essentially contribute to the entanglement of the structures through extensive hydrogen bonding. Magnetic measurements for 2 indicate that very weak ferromagnetic interactions are operative between anisotropic Co(II) centers via sulfate bridges.