Ab initio calculations on cis-[PtCl2(PMe3)2]:: Search for a model chemistry for platinum(II) complexes

The capacity of Hartree-Fock (HF), Moller-Plesset second order perturbation (MP2), and density functional (DF) calculations to predict the experimental dipole moment and the metal-ligand bond lengths of a planar platinum(II) complex, cis[PtCl2(PMe3)(2)], was investigated. Highly erroneous results were obtained from uncorrelated HF calculations and from MP2 and DF calculations which included the 5s and 5p electrons of platinum in a frozen core or in an effective core potential. DF calculations including these (n-1)s and (n-1)p electrons in the valence space are shown to have the ability to correctly reproduce the platinum-ligand bond lengths and the dipole moment, provided that sufficiently large basis sets including polarization functions are used. MP2 calculations yielded dipole moments comparable to those obtained from DF calculations with the same basis set and reproduced better the difference between the Pt-Cl and Pt-P bond lengths, but required 2-6 times more computer time. The best agreement between calculated and experimental dipole moment and bond length values was obtained with DF calculations using the program ADF, provided that the scalar relativistic terms were included in the hamiltonian. Our results indicate that the mutual influence of the platinum-ligand bonds in trans-position (the so-called trans-influence) involves both electron correlation and relativistic effects.