[(ETA-2-C2H4)OS(CO)4] AS A VIBRATIONAL MODEL FOR TYPE-I' ETHENE CHEMISORBED AS A METALLACYCLOPROPANE ON METAL-SURFACES

A comprehensive vibrational assignment of the hydrocarbon features in the infrared and Raman spectra of (eta2-C2H4)Os(CO)4 has been achieved with the help of data from the ((C2H4)-C-13) and (C2D4) isotopologues . Close analogies with the vibrational spectra of thiirane (ethene sul fide) assist in the assignment and emphasize the metallacyclopropane n ature of the (C2H40s) group. Comparisons are made with analogous spect ra from (eta2-C2H4)Fe(CO)4 and from Zeise's salt, K[(eta2-C2H4)PtCl3]. Taking into account the metal-surface selection rule associated with on-specular vibrational electron energy loss or reflection-absorption infrared spectra, good agreement is found between the wavenumber/inten sity pattern from the a1 modes of the complex and from ethene chemisor bed on metal surfaces previously designated Type I'.