A unique open inorganic-organic framework with alternate hexa- and penta-coordinate cobalt(II) sites. Synthesis, crystal structure and magnetic properties of [Co-3(C4H4O4)(2.5)(OH)](n)center dot 0.5nH(2)O

A three-dimensional open-framework with unprecedented alternate hexa- and p enta-coordinate cobalt(a) sites was obtained from the hydrothermal reaction of cobalt nitrate and succinate in a basic solution. Of the four crystallo graphically independent Co(a) atoms in the crystal structure of this compou nd, three are hexa-coordinated and one penta-coordinated. The cobalt(II) at oms are linked by edge-sharing CoOn (n = 5 or 6) polyhedrons. The temperatu re dependence of the magnetic susceptibility of this compound shows strong antiferromagnetic interaction between the metal atoms.