HOMO-LUMO gap in Pt(II)

[Jirka Kozelka <kozelka : at : citi2.fr>]

Dear CCL-members,
 I have carried out a number of SCF calculations on Pt(II) complexes with
 chloride, amine, and phosphine ligands, using Gaussian 94 and 98, with
 different basis sets, and find consistently HOMO-LUMO gaps of 0.3-0.4
 Hartrees, i.e., 65000-90000 cm-1. This is roughly 3 times the excitation
 energies of spin-allowed d-d bands seen in
 solutions of these species. The difference seems too big to me to be
 explained by electron relaxation. I would very much appreciate comments
 and/or explications on/of this apparent discrepancy.
 We have seen that the bond lengths and dipole moment coming from HF
 calculations are quite wrong for these compounds, and one has to apply
 correlated methods to get these quantities right. But can it be that the
 difference in energies of the HF HOMO/LUMO one-electron orbitals is so
 far from the excitation energy?
 I shall summarize the answers.
 Thanks,
 Jirka Kozelka
 --
 Jirka Kozelka
 Universite Rene Descartes
 URA CNRS 400
 45 rue des Saints-Peres
 75270 Paris 06
 FRANCE
 Tel. +331 42 86 21 75
 Fax  +331 42 86 83 87
 E-mail: kozelka : at : citi2.fr