Ab initio on Ir(IV), Os(IV) and Ru(III, IV)

[Achim Lienke <achim' at \`psipsy.uct.ac.za>]

 I am calculating a series of chloro and aqua-chloro complexes of
 Platin-Group-Metals (PGMs) (e.g. PtCl6-2, RhCl6-3, IrCl6-2) with ab
 initio methods in order to obtain geometries, IR frequencies and point
 charges.
 The results for all closed shell systems are good and reflect
 experimental data and trends, but for the open-shell systems like
 IrCl6-2 and OsCl6-2 this is probably not the case. There is a slight
 Jahn-Teller distorsion (which is expected), but the avaraged bond
 lengths are smaller than expected and - more important - the point
 charges on the axial and equatorial chlorines differ substantially and
 are larger than one would expect from experimental data (solvation).
 My question: Can it be that those results are just artefacts because
 some important effects and couplings are neglected? I am using Gaussian
 94, Methods are SVWN (produces good results), B3LYP and MP2 (to check,
 methods are in for this application inferior), basisset is LANL2DZ for
 the metal and 6-31G for Cl, H and O
 Achim Lienke
 Department of Chemistry
 University of Cape Town
 achim' at \`psipsy.uct.ac.za