Crystal and molecular structure of a tetranuclear cobalt(II)–tropolonate complex: [Co4(C7H5O2)8(H2O)2]

Abstract

Crystals of the title compound are monoclinic, a= 13.341 (5), b= 18.634(9), c= 11.603(5)Å, β= 171.43(3)°, Z= 2, space group P2₁/c. The structure was determined from X-ray diffractometer data by Patterson and Fourier syntheses, and refined by full-matrix least-squares calculations to R 0.067 for 2 070 observed reflections. There are two distinct cobalt atoms in the structure, both achieving a co-ordination number of six but with considerably distorted octahedral geometry. Of the four independent tropolone ligands in the asymmetric unit, three chelate and have one bridging oxygen atom while the other ligand chelates and does not bridge. A water molecule completes the co-ordination polyhedra. The Co–O distances vary from 2.051 (6) to 2.1 49(9)Å, with mean distances corresponding to whether the ligand chelates (2.060 Å), chelates and bridges (2.084 Å), or forms a bridging bond (2.137 Å). The molecules are hydrogen-bonded via the water molecules and tropolone oxygen atoms. The stability of the structure is due to efficient lattice packing and hydrogen bonding, both facilitated by the compact planar structure of the ligand.