Tetrahedral gold–phosphine clusters: a relativistic molecular orbital study

Abstract

The recently characterized cluster [{Au(PBu₃^t)}₄]²⁺ has been investigated by the quasi-relativistic and relativistic versions of the LCAO-SCF molecular orbital approach at the non-empirical CNDO/1 level. The optimized geometry agrees well with available experimental data. The naked gold cluster alters its properties dramatically when phosphine ligands are added. The simple phosphine PH₃ is a rather poor model of more complex phosphines, like PBu^t₃. The former is not capable of sufficient donation and thus it induces an instability with respect to reduction. The polar environment assists positively in the redox stabilization of the cluster. The effect of the phosphine ligands lies in the saturation of the high electron affinity of the {Au₄}²⁺ core and in the population of the d_5//2 sublevel.