Three Ni/Co(II) complexes with 4,4′-bipyridine and benzoic acid derivatives as mixed coligands:: Hydrothermal syntheses, structures, and magnetisms

The hydrothermal reactions of 3,5-dinitrobenzoic acid, or p-toluic acid, 4,4'-bipyridine, with transition metal chlorides in basified solvent gave rise to three coordination polymers, [Ni-2(3,5-DNBC)(4)(4,4'-bpy)(2)(H2O)] (1), [Co(3,5-DNBC)(2)(4,4'-bpy)(2)] (2), [Co-3(4,4'-bpy) (p-ToC)(6)] (3), and characterized by elemental analysis, IR, single-crystal X-ray diffraction and variable-temperature magnetic measurements. Compound 1 crystallizes in the monoclinic system, P2(1)/c space group, the structure determination reveals that 1 has a 2D network based on lozenge grids, where each Ni-II is in 4O + 2N coordination mode. Compound 2 is also monoclinic system, P2/c space group, and the X-ray structural analysis shows that 2 also has a 2D network but based on rectangular grids with the Co-II atom in a CoN2O4 environment. Compound 3 crystallizes in the triclinic system, P (1) over bar space group, and polymerizes through nitrogen and oxygen atoms giving 1D chains with the Co-II(1) atom in a CoO6 environment and Co-II(2) is in N + 4O coordination mode. In good agreement with the expected behavior, magnetic susceptibility measurements show weak ferromagnetic interactions for 1 and 3, whereas compound 2 exhibits moderate antiferromagnetic coupling. (C) 2007 Published by Elsevier B.V.