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 [{Co3(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 P1- with a = 8.2620(11) Å, b = 10.4409(12) Å, c = 11.0840(10) Å, α = 111.332(8)°, β = 91.394(10)°, γ = 91.638(10)°, Z = 2, V = 889.65(18) Å3. A structure refinement showed that complex 1 is the first example of a two-dimensional (2D) framework with both carboxylate bridges and μ-hydroxo bridges, in which cobalt atoms adopt square-pyramidal and square-planar geometries. Complex 1 exhibited a interesting magnetic behavior: the shape of the μeff 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.