Despite the importance of group 6 metal-centered 17-electron radicals CpM(CO)3• (M = Cr, Mo, W) in establishing many of the fundamental reactions now known for metal-centered radicals, spectroscopic characterization of their electronic properties and structures has been very challenging, due to their high reactivity. Here we report a gas-phase study of these species by photodetachment photoelectron spectroscopy (PES) of their corresponding 18-electron anions and by theoretical electronic structure calculations. Three well-separated spectral features are observed by PES for each anionic species. Electron affinities (EAs) of CpM(CO)3 • were experimentally measured from the threshold of each spectrum and were found to be 2.38 ± 0.02 (M = Cr), 2.63 ± 0.02 (Mo), and 2.63 ± 0.01 eV (W). These experimental values correlate well with the reported redox potentials measured in solution. Theoretical calculations for all anionic and neutral (radical) species gave calculated EAs and band gaps that are in good agreement with the experimental data. Molecular orbital (MO) analyses for each anion indicate that the top three occupied MOs are mainly metal-based and contribute to the first spectral feature, whereas the next two MOs are associated with Cp-M π bonding and contribute to the second spectral feature. The calculations further exhibit appreciable anion-to-neutral structural changes for all three species, with the change for the W species being the smallest.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry