Syntheses, structures, and magnetic properties of cobalt(II) and nickel(II) coordination polymers based on a V-shaped ligand

Two coordination polymers [Co-2(TA)(4,4'-bipy)(2)(H2O)(2))]center dot H2O (1) and [Ni-2(TA)(4,4'-biPy)(2)(H2O)(4)]center dot 3H(2)O (2) were prepared by hydrothermal reactions of MCl2 center dot 6H(2)O (M = Co, Ni) with a V-shaped ligand TDPA (3,3',4,4'thiodiphthalic anhydride) and a I-shaped N-donor co-ligand (4,4'-bipy). They were characterized by elemental analyses, thermogravinetric analyses, and magnetic behavior. As is expected, TDPA hydrolyzes into the corresponding tetra-carboxylate acid H(4)TA (3,3',4,4'-thiodiphthalic acid) during the reactions. Co-2 dimer and Ni mononuclear center are connected into two-dimensional (2D) layers by H(4)TA and 4,4'-bipy bridge in 1 and 2, respectively. The most amazing feature is that 1 and 2 exhibit interesting spin-canting metamagnetism and weak ferromagnetic behavior, respectively, with the critical Neel temperature of T-N =4 K for 1 and T-N =13 K for 2, based on variable temperature magnetic susceptibility measurements. In low mono- or dinuclear metal system, such magnetic behaviors have rare been observed. Furthermore, complex 1 will be a potential metamagnet material.