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

Three 3D supramolecular networks, [Co­(H2L1)2]·(SO4)·2H2O (1), [Co­(H2L1)­(SO4)­(H2O)­(DMF)] (2),
and [Co­(H2L2)­(SO4)­(H2O)] (3), were prepared by reacting Co­(II) sulfate with the rigid bis-imidazoles
of 1,4-di­(1H-imidazol-4-yl)­benzene (H2L1) and 1,3-di­(1H-imidazol-4-yl)­benzene (H2L2) in solvothermal conditions. Compounds 1 and 2 containing the H2L1 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 H2L1. When H2L2 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 H2L2-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.