Effects of bridging hydrogens on metal-metal bonds. 2. UV photoelectron and UV-visible spectra and quantum chemical calculations for Fe3(.mu.-H)3(CO)9(.mu.3-CMe) and Co3(CO)9(.mu.3-CMe)

Abstract

The valence-level photoelectron spectrum of Fe/sub 3/(..mu..-H)/sub 3/(CO)/sub 9/(..mu../sub 3/-CCH/sub 3/) (II) has been measured in the gas phase with He I and Ne I radiation, and the UV-visible spectrum has been measured in solution. The observed bands in the former are assigned on the basis of model compound spectra, intensity changes with photon energy, and relative band areas. Comparison of the results with similar measurements on isoelectronic Co/sub 3/(CO)(..mu../sub 3/-CCH/sub 3/) (I) reveals significant differences associated with the presence of the bridging H atoms in II. These are described in terms of protonation of the M-M bonds in going from I to II. Molecular orbital calculations of the Fenske-Hall type on I and II corroborate both the assignment of the spectra and the differences in going from I to II. Examination of the results of Mulliken population analyses and selected orbital contour diagrams clearly demonstrates the essential localized, hydridic, and ligandlike behavior of the bridging H atoms in II. The calculations on I and II also demonstrate that the cluster bonding of Co(CO)/sub 3/ and Fe(CO)/sub 3/ fragments in these molecules is adequately represented by CH and BH fragments. 8 figures, 3 tables.