Aurophilic attraction and luminescence of binuclear gold(I) complexes with bridging phosphine ligands: ab initio study.

Electronic structure and spectroscopic properties of [Au2(dpm)2]2+ (dpm = bis(diphosphino)methane) were studied by ab initio calculations. The absorption and emission spectra of this binuclear gold(I) complex in acetonitrile and in the solid state were calculated by single excitation configuration interaction (CIS) method. In the calculations, the solvent effect was taken into account by the weakly solvated [Au2(dpm)2]2+ x (MeCN)2 complex. The ground state structures of [Au2(dpm)2]2+ and [Au2(dpm)2]2+ x (MeCN)2 were optimized by the second-order Møller-Plesset perturbation (MP2) method, while the emissive triplet excited state structures were optimized by the CIS calculations. The results reveal that coordination of acetonitrile to the gold atom in the 3[d(sigma*)s(sigma)] excited state causes a significant red shift in emission energy. The weak aurophilic attraction exists in the ground states of [Au2(dpm)2]2+ and [Au2(dpm)2]2+ x (MeCN)2, and is greatly enhanced in their 3[d(sigma*)s(sigma)] excited states. In acetonitrile, the 3Au(s(sigma)) --> 1Ag(d(sigma*)) transition (phosphorescence) of [Au2(dpm)2]2+ was calculated at 557 nm, in consistent with the observed emission of [Au2(dppm)2](ClO4)2 (dppm = bis(diphenylphosphino)methane) at 575 nm. A high energy emission at 331 nm is predicted for [Au2(dpm)2]2+ in the absence of the interaction between the gold atom and solvent molecule and/or neighboring anion in the excited state. The CIS calculations on the excited states also reveal that the two absorption bands at 278 and 218 nm recorded for [Au2(dcpm)2](ClO4)2 in acetonitrile can be attributed to the 1Ag(d(sigma*)) --> 1Au(p(sigma)) and 1Ag(d(sigma*)) --> 1Au((sp)sigma) transitions, respectively.