ELECTRONIC ABSORPTION AND MCD SPECTRA FOR THE AU8(PPH3)82+ ION

Electronic absorption and magnetic circular dichroism (MCD) spectra in the vis-UV range 1.66-3.60-mu-m-1 are reported for [Au8(PPh3)8](NO3)2 in acetonitrile solution at room temperature. The MCD spectrum consists of both A and B terms and adds important detail to a consideration of the absorption spectrum. The spectra are interpreted in terms of a MO model in which skeletal bonding in the C3v cluster complex is described by sigma-interaction among 6s atomic orbitals of the gold atoms. The lowest energy excited states are ascribed to intraskeletal transitions. Evidence is also presented for a Au 5d --> 6s skeletal transition in the spectra for Au8(PPh3)8(2+). Differences observed between the spectra for Au9(PPh3)8(3+) and Au8(PPh3)8(2+) are also discussed.