Two CoII coordination polymers of biphenyl-2,2',5,5'-tetracarboxylic acid with flexible N-donor ligands: syntheses, structures and magnetic properties

Two Co-II-based coordination polymers, namely poly[(mu(4)-biphenyl-2,2',5,5'-tetracarboxylato){mu(2)-1,3-bis[(1H-imidazol-1-yl) methyl] benzene} dicobalt(II)], [Co-2(C16H6O8)(C14H14N4)(2)](n) or [Co-2(o, m-bpta)(1,3-bimb)(2)](n) (I), and poly[[aqua(mu(4)-biphenyl-2,2',5,5'-tetracarboxylato){1,4-bis[(1H-imidazol-1-yl) methyl]-benzene} dicobalt(II)] dihydrate], {[Co-2(C16H6O8)(C14H14N4)(2)(H2O)(2)]center dot 4H(2)O} n or {[Co-2(o, m-bpta)(1,4-bimb)(2)(H2O)(2)]center dot 4H(2)O}(n) (II), were synthesized from a mixture of biphenyl-2,2',5,5'-tetracarboxylic acid, i.e. [H-4(o,m-bpta)], CoCl2 center dot 6H(2)O and N-donor ligands under solvothermal conditions. The complexes were characterized by IR spectroscopy, elemental analysis, single-crystal X-ray diffraction and powder X-ray diffraction analysis. The bridging (o, m-bpta)(4-) ligands combine with Co-II ions in different mu(4)-coordination modes, leading to the formation of one-dimensional chains. The central Co-II atoms display tetrahedral [CoN2O2] and octahedral [CoN2O4] geometries in I and II, respectively. The bis[(1H-imidazol-1-yl) methyl] benzene (bimb) ligands adopt trans or cis conformations to connect Co-II ions, thus forming two three-dimensional (3D) networks. Complex I shows a (2,4)-connected 3D network with left-and right-handed helical chains constructed by (o, m-bpta)(4-) ligands. Complex II is a (4,4)connected 3D novel network with ribbon-like chains formed by (o, m-bpta)(4-) linkers. Magnetic studies indicate an orbital contribution to the magnetic moment of I and II due to the longer Co center dot center dot center dot Co distances. An attempt has been made to fit the chi T-M results to the magnetic formulae for mononuclear Co-II complexes, the fitting indicating the presence of weak antiferromagnetic interactions between the Co-II ions.