Theoretical evidence for transannular metal-metal interactions in dinuclear coinage metal complexes

The dinuclear head-to-tail complexes [M-2(PPh2CH2SPh)(2)](2+) (M = Cu (1), Ag (2a, 2b), Au (4)) are obtained either by reaction of [Cu(CH3CN)(4)]CF3SO3, AgClO4, AgCF3SO3, with equimolecular amounts of PPh2CH2SPh or of [AuCi(PPh2CH2SPh)] (3), prepared by reaction of [AuCl(tht)] and PPh2CH2SPh, with AgCF3SO3. The crystal structures of complexes 2a and 4 have been established by X-ray diffraction studies. Ab initio HF/II and MP2/II calculations have been performed on the [M-2(H2PCH2SH)(2)](2+) model, indicating that metallophilic attraction is indeed present for all the coinage metals as a correlation effect and is strengthened in the case of gold by relativistic effects. Since experimental and theoretically predicted geometries are in close agreement, we assume that our calculations are accurate enough to obtain valid conclusions.