Structure of tetrakis(phosphine)nitrido- or -phosphinidyne or arsinidyneultragold(1+): Td or C4v?

Quasirelativistic pseudopotential methods at HF and MP2 levels are used for optimizing the geometry of the title compounds. The naked clusters EM 4 + (M=H, Ag, Au) are also considered. In agreement with experiment, N(AuPH 3 ) 4 + is T d and the As(AuPH 3 ) 4 + ion is a C 4v . The calculated MP2 Au...Au distance for E=As is 296 (experimental 290) pm, and the Au-As-Au is angle 69.1 (70.7) o . The bonding is analyzed. The secondary Au...Au bond is attributed to correlation, not 5d6s6p hybridization