Solid-state and solution conformation of a new cobalt dimer µ-form-amido-bis[penta-amminecobalt(III)] pentachloride monohydrate: X-ray and kinetic studies

Abstract

The crystal and molecular structure of the title compound has been determined by three-dimensional X-ray analysis. Crystals are triclinic, space group P, with Z= 2 in a unit cell of dimensions: a= 6.981(8), b= 14.346(8), c= 11.992(6)Å, α= 99.41(4), β= 103.68(9), γ= 93.11(7)°. The structure was solved by the heavy-atom method and refined by full-matrix least-squares calculations to R 0.082 for 922 observed reflections measured by diffractometer. The crystal structure consists of discrete cations, anions, and water molecules separated by normal distances. In the cation the octahedrally co-ordinated cobalt atoms are linked by the bidentate formamido-ligand which has a cis-conformation of the NH and CH groups. Co–N(formamido) Is 1.94(2), and the mean of the other Co–N bonds is 1.99(2)Å. Other bond lengths are Co–O 1.92(2), C–O 1.26(3), and C–N 1.34(4)Å.

The cation is shown to have the same cis-conformation in solution (from nuclear Overhauser studies) as that found in the solid state. Kinetics of reduction show that the complex is reduced by an initial outer-sphere mechanism.