ESR investigation of paramagnetic carbonyl-metal clusters of high nuclearity

An ESR study has been made of the high nuclearity paramagnetic metal cluster anions [Rh12(CO)13(μ2-CO)10(C)2]3-, [Co13(CO)12(μ2-CO)12(C)2]4- and [Co6(CO)8(μ2-CO)6C]-. The assignment of the HOMO is based on a mixed valence model which relates the g tensor components of cluster systems to those of an appropriate conventional paramagnetic center. With this model the HOMOs of [Rh12(CO)13(μ2-CO)10(C)2]3- and of [Co13(CO)12(μ2-CO)12(C)2]4- are found to be mainly comprised of metal dz2 atomic orbitals, while for [Co6(CO)8(μ2-CO)6C]- a large overlap between d atomic orbitals and ligand orbitals is suggested. The occupation of the valence molecular orbitals deduced from the ESR data is consistent with the variations in MM bond distance observed by X-ray analysis. © 1982.