Comparative calculations for the A-frame molecules [S(MPH3)2] (M = 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.