| Research Abstract |
A large number of phosphine and arsine complexes of a Lewis hard metal ion, Co(III) have been prepared, and their structure determination including X-ray analysis, and spectroscopic, photo- and electro-chemical studies have been carried out. The Co(III) complexes have, in general,filled dpi^6 (HOMO) and vacant dsigma (LUMO) orbitals, and thier energies approximately correspond, respectively, to oxidation and reduction potentials of the complexes. These potentials were largely dependent on the charge of complex ion, but the potential differences between them showed a good linear relation with transition energies of the first ligand field band. Thus one can estimate the dsigma and dpi energies of Co(III) complexes from the electro-chemical and absorption spectral data, and can discuss the donor and acceptor properties of ligands. From measurements of a number of amine, phosphine, and arsine complexes of the same type, it was concluded that the sigma-donor properties increase in the order of -PMe_2>-NH_2, -AsMe_2>-NMe_2. The dpi orbital energies were concluded to be destabilized in the order of -PMe_2>-AsMe_2>-NH_2,-NMe_2 by the pi-type donation of these coordination groups. Phosphine and arsine ligands seem to act as a pi-donor rather than a pi-acceptor towards hard metals such as Co(III) and destabilize the dpi orbitals of the metal ion.
The cis-[Co(dtc)_2{P(OR)_3}_2]^+-type complexes(dtc=dithiocarbamate ion) isomerized to the trans isomer by exposure of ultraviolet light in solution, but regenerated the original cis isomer in the dark. The isomerization also occured by electrochemical reduction to Co^<2+> and Co^+to give a equilibrium mixture of cis and trans isomers. No such isomerization properties were observed for the corresponding phosphine complexes.
|
