An inelastic neutron scattering study and re-assignment of the vibrationalspectrum of [Os-3(CO)(9)(mu(2)-CO)(mu(3)-eta(2)-C2H2)], a model compound for chemisorbed ethyne

The complex [Os-3(CO)(9)(mu(2)-CO)(mu(3)-eta(2)-C2H2)] (1) has been used as a vibrational model compound for the bonding of ethyne on metal single cry stal surfaces. The original vibrational assignment of the ethyne ligand in 1 was based on the infrared and Raman spectra of the protonated and deutera ted complexes and comparison with the spectra of related compounds. We have now measured the inelastic neutron scattering (INS) spectrum of the comple x, and the assignment of the C-H bending and the Os-C stretching modes of 1 has been partially revised in the light of this. Since the revisions large ly affect the antisymmetric modes, (A "), the conclusions from previous wor k regarding the assignment of the type B (di-sigma/pi) ethyne chemisorption on metal single crystals are still valid.