Electronic structure of the {Pd Cl4}2-ion

The structure of the {Pd Cl4}2- anion was calculated within a non-empirical pseudopotential model, using the PSHONDO program. The molecular orbital ordering is compared with previous calculations using CNDO, INDO, X α and other semiempirical schemes. A comparison with the photoelectron spectra is carried out. It is argued that the simplified molecular orbital identification proposed in semiempirical studies to reproduce such spectra is not unique and the application of Koopmans' theorem to this complex is questioned; consequently a new identification is here proposed that correlates well with the experimental data. Several other ab initio studies on different square planar complexes are reviewed, showing the same trends and conclusions reached in the present work.