Variable-energy photoelectron spectroscopy of thin film Mo2(O2CCH3)4 on a GaAs substrate in ultrahigh vacuum is used to examine the valence ionizations of the quadruple metal-metal bond. The changes in photoionization cross sections with photon energy over a range of 40 to 90 eV are examined. The metal-based σ, π, and δ ionizations of the quadruple bond are strongly enhanced relative to the acetate-based ionizations in the region of photon energies from 40 to 50 eV. This is consistent with a molybdenum 4p to 4d resonance and super-Coster-Kronig Auger enhancement of the metal-based ionizations. The extent of resonance enhancement is related to the amount of Mo 4d character associated with the ionization. The π ionization of the Mo-Mo quadruple bond has the largest contribution from the Mo 4d orbitals. The δ and σ ionizations of the metal-metal bond contain smaller amounts of Mo 4d character, and some Mo 4d character is observed in the acetate-based ionizations. This is explained in terms of significant overlap and mixing of the δ and σ components with the ligand orbitals. Also, in the case of the a component, there is a possible filled/filled interaction between the Mo 4dz2 orbital on one metal and the Mo 4pz orbital on the adjoining metal. These interactions have significant impact on the properties of these complexes.
ASJC Scopus subject areas
- Colloid and Surface Chemistry