Electron structure of [{Ni(η⁵-C₅H₅)(μ-CO)}₂] by He(I) and He(II) photoelectron spectroscopy

The electronic structure of the title compound is discussed on the basis of the He(I) and He(II) excited photoelectron spectra and extended Hückel calculations. The compared He(I) and He(II) band intensities proved to be of crucial importance in order to assign the very complicated spectral pattern. The most interesting result of this study is the observation that four metal-based d electrons are strongly involved in two back-bonding interactions to bridging carbonyl π* molecular orbitals which are localized respectively in- and out-of-the-plane defined by the Ni₂(CO)₂ core.