Theory of d10−d10 Closed-Shell Attraction. III. Rings

We study the dependence of the intramolecular M I −M I interaction on electron correlation effects in eight-membered rings of type [M 2 (PH 2 CH 2 PH 2 ) 2 ] 2+, [M 2 (NHCHNH) 2 ], [M 2 (SCHS) 2 ] (M = Au, Ag, Cu), [Au 2 (PH 2 CH 2 PH 2 ) 2 ]Cl 2, halogenometal(I) [M 2 X 4 ] 2 - (M = Au, Ag, Cu; X = Cl, Br, I), and [Au 2 Te 4 ] 2 - at the quasirelativistic pseudopotential ab initio MP2 and Hartree−Fock levels. The intramolecular M I −M I distances, R, at the MP2 level fall in the same range as the experimental ones. The R values are reduced from HF to MP2 level. All the calculations suggest that correlation effects are essential. The reduction of R depends on the particular M−L combination (L = ligand). In the rings, short Cu I −Cu I distances are recovered for the first time. The explicit inclusion of the counterions is unimportant for M I and essential for M II, as shown by a study of the oxidative addition of Cl 2 to the model [Au 2 (CH 2 PH 2 CH 2 ) 2 ]. The Au(I) is then oxidized to Au(II), and the Au−Au distance is shortened to 261 pm, corresponding to a σ bond. This value is in agreement with experiment.