Three two-dimensional cobalt(II) and nickel(II) coordination polymers with dinuclear secondary building units constructed by one unsymmetric dicarboxylic acid: Synthesis, structures, and magnetic property

Hydrothermal synthetic methods using pyridine (py) and 4-methylpyridine (4-mpy) as weak bases and small terminal ligands generated three CoII and NiII 2D coordination polymers with dinuclear metal clusters as secondary building units (SBUs) from an organic bridging ligand, biphenyl-2, 4′-dicarboxylic acid (H2L). These compounds are [Co2(L)2(py)4(H2O)]n (1), [Ni2(L)2(py)4(H2O)]n (2), and [Ni2(L)2(4-mpy)4(H2O)]n (3). Compounds 1 and 2 which both crystallize in the monoclinic space group P21/c are structural isomorphous, while 3 crystallizes in the monoclinic space group C2/c. Further structural analysis indicates that they all possess the (4, 4) grid layered structure. Magnetization studies show antiferromagnetic coupling for 1 (−E2/k = −6.7 K). Finally, thermal analyses have been performed on these compounds via TG and DTG curves.