THE ELECTRONIC STRUCTURES AND REACTIVITIES OF Mn(CO)5X COMPLEXES

Abstract

The bonding in Mn(CO)5X complexes is described in terms of molecular orbitals. The axial CO group is assumed to be bonded much more strongly to Mn than the other four CO groups. The molecular orbital energy level scheme thus derived successfully accounts for the principal features of the electronic spectra of Mn(CO)5X complexes in different solvents. The first charge transfer band is assigned as an n(Mn) → π*(CO) type transition. This n → π* assignment is supported by the fact that the maximum of the band for Mn(CO)5Br is shifted to higher energies on increasing the polarity of the solvents employed.Kinetic studies of Mn(CO)5X-14CO exchange reveal that the axial CO is more inert than the other four CO groups; also, the rates of 14CO exchange of the four equivalent CO groups in Mn(CO)5X complexes depend strikingly on the nature of the X− ligand. A consistent interpretation of the above results and the observed kinetics of some typical substitution reactions of Mn(CO)5X complexes is presented in terms of the derived electronic structural description.