Comparative calculations for the A-frame molecules [S(MPH3)2] (MÂ =Â Cu, Ag, Au) at levels up to CCSD(T)

The geometries of the A-frame molecules S(MPH3)2 (M = Cu, Ag, Au) are optimized at the HF, MP2, MP3, MP4, CCSD, and CCSD(T) levels using 19-valence-electron pseudopotentials. The M-M distances show oscillations which increase in the order Ag < Au < Cu. This result qualitatively parallels recent findings for the metallophilic bond strength by O'Grady and Kaltsoyannis [E. O'Grady, N. Kaltsoyannis. Phys. Chem. Chem. Phys. 6 (2004) 680.]. Local MP2 and local CCSD calculations were also performed for comparison. These methods allow to partition the correlation contributions to the M-M interaction energy into dispersion and ionic terms. The latter were found to be unprecedently important for M = Cu.