Abstract

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 2CH 2PH 2) 2] 2+, [M 2(NHCHNH) 2], [M 2(SCHS) 2] (M = Au, Ag, Cu), [Au 2(PH 2CH 2PH 2) 2]-Cl 2, halogenometal(I) [M 2X 4] 2- (M = Au, Ag, Cu; X = Cl, Br, I), and [Au 2Te 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 2PH 2CH 2) 2]- The Au(I) is then oxidized to Au(II), and the Au-Au distance is shortened to 261 pm, corresponding to a ? bond. This value is in agreement with experiment.