Photoelectron spectroscopy of dimolybdenum tetracarboxylates: Probing the electronic nature of the molybdenum-molybdenum quadruple bond

Abstract

Photoelectron spectroscopy is used to investigate the electronic structure of molybdenum-molybdenum quadruple bonds in dimolybdenum tetracarboxylates. The variable energy photoelectron spectra of the valence region of dimolybdenum tetraacetate are reported for a range of incident photon energies. The pi components of the metal-metal bond contain the most molybdenum 4d character. The sigma component has contribution from both the ligand and the molybdenum 4p orbitals on the adjoining molybdenum. The delta component has significant overlap with the ligand orbitals. A comparative gas phase and surface ultraviolet photoelectron study of dimolybdenum tetrabenzoate is also reported. This is the first dimolybdenum tetracarboxylate where the ligand is capable of large resonance overlap with the metal center. There is significant orbital overlap between the ligand and the metal-metal bond, especially with the delta component. Both of these studies show that there is electronic communication between the metal-metal bond and the carboxylate ligand.