A unique two-dimensional terephthalate-bridged structure with alternate tetra- and penta-coordinate cobalt(II) sites.: Synthesis, crystal structure and magnetic properties of [{Co3(tP)2(OH)2(phen)2}n]

A two-dimensional (2D) cobalt coordination polymer [{Co-3(tp)(2)(OH)(2)(phen)(2)}(n)] (1), bridged by the terephthalate (tp) ligand, was synthesized under hydrothermal conditions, and its structure was determined by single-crystal X-ray diffraction. Complex 1 crystallized in the triclinic space group P (1) over bar with a = 8.2620(11) Angstrom, b = 10.4409(12) Angstrom, c = 11.0840(10) Angstrom, alpha = 111.332(8)degrees, beta = 91.394(10)degrees, gamma = 91.638(10)degrees, Z = 2, V = 889.65(18) Angstrom(3). A structure refinement showed that complex I is the first example of a two-dimensional (21)) framework with both carboxylate bridges and mu-hydroxo bridges, in which cobalt atoms adopt square-pyramidal and square-planar geometries. Complex 1 exhibited a interesting magnetic behavior: the shape of the mu(eff) curve indicates a ferrimagnetic-like behavior between 300-41.0 K, immediately followed by a strong decay of the magnetic moment. Moreover, complex 1 was characterized by IR spectroscopy, inductively coupled plasma (ICP), elemental and thermogravimetric (TGA) analyses.