The first examples of vibrational structure in metal-ligand σ-bond ionizations are observed in the gas-phase photoelectron spectra of CpRe(NO)(CO)H and Cp*Re(NO)(CO)H [Cp = η5-C5H5, Cp* = η5-C5(CH3)5]. The vibrational progressions are due to the Re-H stretch in the ion states formed by removal of an electron from the predominantly Re-H σ-bonding orbitals. A vibrational progression is also observed in the corresponding ionization of the deuterium analogue, Cp*Re(NO)(CO)D, but with lower vibrational energy spacing as expected from the reduced mass effect. The vibrational progressions in these valence ionizations are directly informative about the nature of the metal-hydride bonding and electronic structure in these molecules. Franck-Condon analysis shows that for these molecules the Re-H or Re-D bond lengthens by 0.25(1) Å when an electron is removed from the Re-H or Re-D σ-bond orbital. This bond lengthening is comparable to that of H2 upon ionization. Removal of an electron from the Re-H or Re-D bonds leads to a quantum-mechanical inner sphere reorganization energy (λQM) of 0.34(1) eV. These observations suggest that even in these low symmetry molecules the orbital corresponding to the Re-H σ bond and the Re-H vibrational mode is very localized. Theoretical calculations of the electronic structure and normal vibrational modes of CpRe(NO)(CO)H support a localized two-electron valence bond description of the Re-H interaction.
ASJC Scopus subject areas
- Colloid and Surface Chemistry