The effect of charge on CO binding in rhodium carbonyls: From bridging to terminal CO

Abstract

The structures of cabonic rhodium carbonyl cluster compounds containing one to six Rh atoms are established by infrared multiple photon dissociation spectroscopy. Comparison with their weld known neutral analogues reveals that ionization of the neutral compounds destabilizes bridge bound CO ligands in Rh-2(CO)(8) and Rh-4(CO)(12), leading to cationic complexes with only terminally bound CO. The destabilization is associated with removal of charge from a highest occupied molecular orbital that is banding with respect to bridge-bound CO. Density functional theory calculations support this conclusion. The results provide a possible insight into electronic promoter effects in catalysis.