Infrared, Raman, and resonance-Raman spectra of [Mo2(O2CCH3)4] and [Mo2(O2CCD3)4]

Abstract

The i.r., Raman, and resonance-Raman spectra of [Mo₂(O₂CCH₃)₄] and [Mo₂(O₂CCD₃)₄] over the range 3 100–50 cm^–1 have been measured, and the bands assigned. The band shifts on deuteriation are discussed in detail. In particular, ν(Mo–Mo) at 404 cm^–1 is insensitive (as expected) to deuteriation, but the wavenumbers of many other modes [apart from the obvious ν(CH), CH₃ deformation, and rocking modes], viz.ν(CC), ρ_r(COO), and δ(OCO), are sensitive to deuteriation. This implies extensive coupling of the ring co-ordinates. Raman spectra at resonance with transitions in the violet and ultraviolet display short overtone and combination-band progressions involving ν(Mo–Mo), ν(Mo–Mo), and ρ_r(COO) which indicate that the geometric changes on excitation occur all around the Mo–O–C–O–Mo rings but are small along any one co-ordinate.