Electronic structure of the d¹ bent-metallocene Cp₂VCl₂: A photoelectron and density functional study

The Cp₂VCl₂ molecule is a prototype for bent-metallocene complexes with a single electron in the metal d shell, but experimental measure of the binding energy of the d electron by photoelectron spectroscopy eluded early attempts due to apparent decomposition in the spectrometer to Cp₂VCl. With improved instrumentation, the amount of decomposition is reduced and subtraction of ionization intensity due to Cp₂VCl from the Cp₂VCl₂/Cp₂VCl mixed spectrum yields the Cp₂VCl₂ spectrum exclusively. The measured ionization energies provide well-defined benchmarks for electronic structure calculations. Density functional calculations support the spectral interpretations and agree well with the ionization energy of the d¹ electron and the energies of the higher positive ion states of Cp₂VCl₂. The calculations also account well for the trends to the other Group V bent-metallocene dichlorides Cp₂NbCl₂ and Cp₂TaCl₂. The first ionization energy of Cp₂VCl₂ is considerably greater than the first ionization energies of the second- and third-row transition metal analogues.