Photoelectron spectra of nitrosyldicarbonyl(η⁵-cyclopentadienyl)chromium and thionitrosyldicarbonyl(η⁵-cyclopentadienyl)chromium. Comparison of the electronic structures of metal-nitrosyl and metal-thionitrosyl complexes

Legzdins and Kolthammer recently reported the preparation and structure of the first organometallic thionitrosyl complex, (η⁵-C₅H₅)Cr(CO)₂NS (I).^1-2 This complex is isoelectronic and basically isostructural with a large group of (η⁵-C₅H₅)M-(CO)₂L complexes, where L is a small molecule or fragment species. We have found that such complexes are highly useful for providing detailed information on the relative bonding and electronic interactions between the metal and the attached ligand.^3-6 Our approach combines high-resolution study of the valence ionizations of the complex in the gas phase with appropriate theoretical calculations. It is useful to compare the thionitrosyl complex with the corresponding nitrosyl complex, (η⁵-C₅H₅)Cr(CO)₂NO (II), and the isoelectronic and basically isostructural manganese carbonyl and thiocarbonyl complexes, (η⁵)Mn(CO)₂CS (III) and (η-⁵)Mn-(CO) (IV). It follows from the results of our similar study on complexes III and IV⁴ that NS should be a better π-accepting ligand than NO, which is interesting since NO is already considered to be a strong π acid. Another very important feature should be the greater interaction of the filled NS orbitals with the metal electrons.