One-electron states in polynuclear transition metal carbonyls

The one-electron states in the polynuclear transition metal carbonyls of Ni and Pt with formula (M3(CO)6)n2- (n=1,2) are studied using the chemical pseudopotential method. The bonding in these systems is approached by first studying the molecular orbitals of the metal cluster (Mn) and carbonyl skeleton fragments (CO)k, before allowing them to interact: the orbitals of these 'prepared' fragments interact rather weakly and remain relatively independent. The main electronic interactions appear to involve metal s and d orbitals and the 'lone pair' (5 sigma ) molecular orbitals of the ligands. The molecular symmetry point group is used to classify the molecular orbitals and the symmetry-allowed (electric-dipole) electronic transitions are obtained and compared with the limited amount of experimental information available for solution absorption spectroscopy.