He I and He II photoelectron spectra of some trifluorophosphine, carbonyl, and hydrido transition metal complexes

Abstract

The He I and He II gas-phase ultraviolet photoelectron (p.e.) spectra of [M(PF₃)₅](M = Fe or Ru), [ReH(PF₃)₅], and [RuH₂(PF₃)₄], together with the He I spectrum of [OsH₂(CO)₄], have been recorded and assigned empirically. The highest energy bands, corresponding to ionisation from the σ(M-L) and ligand localised orbitals, are separated from the predominantly metal-based bands by bands associated with the metal–hydrogen bonding orbitals (where present). For the [M (PF₃)₅] complexes, evidence is presented for significant phosphorus character in the e′(highest occupied molecular orbital) level, indicating a greater metal–phosphorus interaction than is found for the e″(second highest occupied molecular orbital) level. The p.e. bands due to ionisation from the M-H localised orbitals of [OsH₂(CO)₄] occur at 11.1 and 11.5 eV, values significantly lower than those found for the bridging hydrido moieties of [Os₃(µ-H)₂(CO)₁₀] and [Os₄(µ-H)₄(CO)₁₂](12.1–12.8 eV). A comparison of the p.e. data reported herein with literature data reveals two trends: a trend towards increasing ionisation energy of the metal d bands in [M (PF₃)_x] complexes with the atomic number of M, and a trend towards lower ionisation energy for the σ(M—H) bands of PF₃ complexes on descending a Group. This latter trend contrasts with the approximately constant, or slightly increasing, ionisation energy associated with the analogous bands of the related hydrido carbonyl complexes.