UV Photoelectron and Theoretical Studies of Organometal Carbonyl Clusters of Ruthenium and Osmium. μ-Hydrido-μ3-Alkynyl Triangulo Cluster Compounds

The electronic structure of μ-hydrido-μ3-alkynyl triangulo clusters of ruthenium and osmium is discussed on the basis of their He I excited vapor-phase photoelectron spectra and on the basis of CNDO quantum-mechanical calculations. The theoretical results contribute to the discussion of the highly complex PE spectra and provide novel insights into the bonding scheme of these molecules. The most interesting feature that emerges from this study is the inadequacy of the usual representation of the molecular structure with three metal-metal bonds since the μ-H-bridged metal atoms show a very low bond overlap population. On the other hand, the commonly accepted qualitative description of the alkynyl-cluster interactions, in terms of one σ bond and two weaker π interactions, receives strong support. Some selected features of the reactivity of these clusters are discussed on the basis of the emerging electronic structural picture.