Electronic structure of metal chalcogen cubane clusters: photoelectron spectroscopic, electrochemical, and theoretical studies of [(.eta.-C5H4Me)TiS]4, [(.eta.-C5H4Me)VS]4, [(.eta.-C5H5)CrO]4, [(.eta.-C5H4Me)CrO]4, [(.eta.-C5H4Me)CrS]4, [(.eta.-C5H4Me)CrSe]4, [(.eta.-C5H4-iso-Pr)MoS]4, and [(.eta.-C5H4-iso-Pr)MoSe

Abstract

He I and He II spectra of [(eta-C5H4iPr)MoS]4, [(eta-C5H4iPr)MoSe]4, [(eta-C5H4Me)CrS]4, [(eta-C5H4Me)CrSe]4, [(eta-C5H4Me)TiS]4, [(eta-C5H4Me)VS]4, [(eta-C5H5)CrO]4, and [(eta-C5H4Me)CrO]4 are presented. The photoelectron spectrum of [(eta-C5H4iPr)MoS]4 has been measured using synchrotron radiation over the photon energy range 21-80 eV. Relative partial photoionization cross section and photoelectron branching ratio data are presented for the first six valence bands (binding energy 5.0-10.5 eV). The cross sections of the d bands show a p --> d giant resonance in the photon energy range 39-60 eV. Intensity variations are interpreted in terms of the atomic orbital contributions to the molecular orbitals from which ionization is occurring. Similarities are observed between the low binding energy (4.8-7.5 eV) regions of the spectra of the sulfur and selenium derivatives of the group 6 elements and are interpreted in terms of ionization from molecular orbitals, composed largely of metal d-orbitals, delocalized over the metal tetrahedron. The molecular ion state ordering 2T2 < 2E < 2A1 is observed, the 2T2 and 2E states showing Jahn-Teller splitting. The a1 and e orbitals are metal-metal bonding whereas the t2 orbitals are nonbonding. Subsequent bands are assigned to cyclopentadienyl pi-orbitals and to metal-chalcogen bonding orbitals. The spectrum of [(eta-C5H4Me)VS]4 is consistent with an a(1)2e4t2(2) ground-state configuration for the metal-based orbitals, ionization from these three orbitals being easily identified. The ground state of [(eta-C5H4Me)TiS]4 cannot be unambiguously assigned from the PE spectrum. The d band region of the [(eta-C5H5)CrO]4 and [(eta-C5H4Me)CrO]4 Spectra shows fewer features. In these cases the metal d electrons are localized on the Cr ions, and the diamagnetism shown at low temperatures is the result of weak antiferromagnetic coupling. Cyclic voltammetry studies on [(eta-C5H4iPr)MoS]4, [(eta-C5H4iPr)MoSe]4, [(eta-C5H4Me)CrS]4, [(eta-C5H4Me)CrSe]4, [(eta-C5H4Me)VS]4, and [(eta-C5H4Me)CrO]4 reveal two reversible oxidations for all of the compounds except [(eta-C5H4Me)CrO]4, which can sustain only one reversible oxidation, consistent with a smaller degree of metal d electron delocalization. Ultraviolet and visible spectroscopy data are presented for [(eta-C5H4iPr)MoS]4, [(eta-C5H4iPr)MoS]4+, [(eta-C5H4Me)CrS]4, and [(eta-C5H4Me)CrS]4+, in which the presence of a band in the spectra of the cations which is not observed in the spectra of the neutral molecules is attributed to a 2A1 <-- 2T2 transition.