A unique open inorganic–organic framework with alternate hexa- and penta-coordinate cobalt(ii) sites. Synthesis, crystal structure and magnetic properties of [Co3(C4H4O4)2.5(OH)]n·0.5nH2O

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