Inelastic neutron scattering studies of benzene-containing organometallic complexes. Part 1. Complexes [Cr(CO)3(η6-C6H6)] and [ Mn(CO)3(η6-C6H6)]Br

Abstract

Inelastic neutron scattering spectra (0–875 cm^–1) of [Cr(CO)₃(η⁶-C₆H₆)](1) and [Mn(CO)₃(η⁶-C₆H₆)]Br (2) have been measured. In addition, low-frequency i.r. (60–600 cm^–1) and Raman (0–l 000 cm^–1) spectra of (2) are reported for the first time. Those low-frequency modes of both compounds which involve significant benzene-ligand displacement have been assigned. From the assignments of the benzene-ligand torsion (ν₂₂) in complexes (1) and (2) to bands at 88.5 and 116.5 cm^–1 respectively, values for the activation energy for benzene-group rotation have been calculated to be 27.5 and 46.5 kJ mol^–1 respectively. In the case of complex (1) this value has been compared with that determined from n.m.r. measurements (17.6 kJ mol^–1).