Sulfate-incorporated Co(II) coordination frameworks with bis-imidazole bridging ligands constructed by covalent and noncovalent interactions

摘要

Three 3D supramolecular networks, [Co(H _2L1) _2] ?(SO _4)?2H _2O (1), [Co(H _2L1)(SO _4)(H _2O)(DMF)] (2), and [Co(H _2L2)(SO _4)(H _2O)] (3), were prepared by reacting Co(II) sulfate with the rigid bis-imidazoles of 1,4-di(1H-imidazol-4-yl)benzene (H _2L1) and 1,3-di(1H-imidazol-4-yl)benzene (H _2L2) in solvothermal conditions. Compounds 1 and 2 containing the H _2L1 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 _2L1. When H _2L2 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 _2L2-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.