Inclusion of relativistic effects into ZDO methods. VI

Quasirelativistic and relativistic (four-component) versions of the CNDO (Complete Neglect of Differential Overlap) methods were used in studying the electronic structure of octahedral 2[CuF6]4-, 2[AuF6]4- complexes and m[Cu6]q, m[Au6]q and m[Au6(PH3)6]q clusters for various charges, q, and spin multiplicities, m. A strong spin-orbit splitting of levels t1u in [Au6]2+ cluster removes the degeneracy of the ground electronic state 3T1g into a nondegenerate state so that the Jahn-Teller instability disappears as a consequence of the relativistic effect. The phosphine ligands change the redox stability of the cluster as the orbital energies are shifted to higher values. On the contrary, the spin-orbit splitting of completely filled t2u levels in [AuF6]4- is irrelevant since the degeneracy of the ground electronic state2Eg (Γ8g in the double group notation) remains unchanged. Consequently the Jahn-Teller instability of the octahedral geometry exists and thus a considerable tetragonal distortion appears. (author). 5 figs., 5 tabs., 22 refs