A vibrational study of the diosmacyclobutene complex Os2(CO)8(μ2–η1,η1–C2H2): The use of organometallic complexes as vibrational models for chemisorbed ethyne

Abstract

The vibrational frequencies of the diosmacyclobutene ring in Os2(CO)8(μ2–η1,η1–C2H2) (1) and its dideuterated isotopologue Os2(CO)8(μ2–η1,η1–C2D2) (1-d2) have been measured and assigned. A normal coordinate analysis shows that the CC bond is weakened relative to those in ethene and cis-disubstituted ethenes, whereas the Os–C bonds are stronger than M–C σ-bonds in related complexes, reflecting back-donation from the osmium d-orbitals into the carbon π*-orbitals in 1. The vibrational frequencies of 1 and other ethyne complexes are compared with the vibrational frequencies of ethyne chemisorbed on metal and silicon single-crystal surfaces.