Electronic Structure of Metal Chalcogen Cubane Clusters: Photoelectron Spectroscopic, Electrochemical, and Theoretical Studies of [(η-C₅H₄Me)TiS]₄, [(η-C₅H₄Me)VS]₄, [(η-C₅H₅)CrO]₄, [(η-C₅H₄Me)CrO]₄, [(η-C₅H₄Me)CrS]₄, [(η-C₅H₄Me)CrSe]₄, [(η-C₅H₄-ⁱPr)MoS]₄, and [(η-C₅H₄-ⁱPr)MoSe]₄

Full title: Electronic structure of metal chalcogen cubane clusters: Photoelectron spectroscopic, electrochemical, and theoretical studies of [(η-C₅H₄Me)TiS]₄, [(η-C₅H₄Me)VS]₄, [(η-C₅H₅)CrO]₄, [(η-C₅H₄Me)CrO]₄, [(η-C₅H₄Me)CrS]₄, [(η-C₅H₄Me)CrSe]₄, [(η-C₅H₄ⁱPr)MoS]₄, and [(η-C₅H₄ⁱPr)MoSe]₄. He I and He II spectra of [(η-C₅H₄ⁱPr)MoS]₄, [(η-C₅H₄ⁱPr)MoSe]₄, [(η-C₅H₄Me)CrS]₄, [(η-C₅H₄Me)CrSe]₄, [(η-C₅H₄Me)TiS]₄, [(η-C₅H₄Me)VS]₄, [(η-C₅H₅)CrO]₄, and [(η-C₅H₄Me)CrO]₄ are presented. The photoelectron spectrum of [(η-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 π orbitals and to metal-chalcogen bonding orbitals. The spectrum of [(η-C₅H₄Me)VS]₄ is consistent with an a₁²e⁴t₂² ground-state configuration for the metal-based orbitals, ionization from these three orbitals being easily identified. The ground state of [(η-C₅H₄Me)TiS]₄ cannot be unambiguously assigned from the PE spectrum. The d band region of the [(η-C₅H₅)CrO]₄ and [(η-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 [(η-C₅H₄ⁱPr)MoS]₄, [(η-C₅H₄ⁱPr)MoSe]₄, [(η-C₅H₄Me)CrS]₄, [(η-C₅H₄Me)CrSe]₄, [(η-C₅H₄Me)VS]₄, and [(η-C₅H₄Me)CrO]₄ reveal two reversible oxidations for all of the compounds except [(η-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 [(η-C₅H₄ⁱPr)MoS]₄, [(η-C₅H₄ⁱPr)MoS]₄⁺, [(η-C₅H₄Me)CrS]₄, and [(η-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.