VIBRATIONAL ASSIGNMENTS FOR METHOXY LIGANDS ON METAL-CLUSTERS - INTERPRETATION OF RAIRS DATA FROM METHOXY GROUPS ON SINGLE-CRYSTAL COPPER SURFACES

Vibrational frequencies of the methoxy groups in the cluster compounds [Re2(mu2-OCH3)3(CO)6] [P(C6H5)4] and [Re3(mu2-H)3(mu3-OCH3)(CO)9][N{P(C6H5)3}2] are assigned using selective deuterium substitution. The nu(s)(CH3) and rho(CH3) modes were found to be the most sensitive to the state of coordination of the methoxy group. A comparison of the cluster data with RAIRS data for methanol adsorbed on Cu(100) and Cu(111) single crystal faces provides a unifying model for the surface methoxy species. This consists of mu2-coordinated methoxy groups tilted to the surface normal on both surfaces at low coverage, but with the tilt angle decreasing with higher surface coverage.