An ab initio study on luminescent properties and aurophilic attraction of binuclear gold(I) complexes with phosphinothioether ligands.

Electronic structures and spectroscopic properties of the binuclear head-to-tail Au(2)(PH(2)CH(2)SH)(2) (1) complex were investigated by ab initio calculations. The solvent effect of the complex in the acetonitrile solution was taken into account by the weakly solvated Au(2)(PH(2)CH(2)SH)(2).(MeCN)(2) (2) moiety in the calculations. The ground-state geometries of 1 and 2 were fully optimized by the MP2 method, while their excited-state structures were optimized by the CIS method. Aurophilic attraction apparently exists between the two Au(I) atoms in the ground state and is strongly enhanced in the excited state. A high-energy phosphorescent emission was calculated at 337 nm for 1 in the absence of the interactions with solvent molecules and/or counteranion in solid state; however the lowest-energy emission of 2 was obtained at 614 nm with the nature of (3)A(u)(s(sigma)) --> (1)A(g)(d(sigma)) (metal-centered, MC) transition. The coordination of acetonitrile to the gold atom in solution results in a dramatic red shift of emission wavelength. The investigations on the head-to-tail Au(2)(PH(2)CH(2)SCH(3))(2) (5) and Au(2)(PH(2)CH(2)SCH(3))(2).(MeCN)(2) (6) moieties indicate that the CH(3) substituent on the S atom causes blue shifts of emission wavelength for 5 and 6 with respect to 1 and 2. By comparison between Au(I) thioether 1 and head-to-tail Au(I) thiolate [Au(2)(PH(2)CH(2)S)(2)] (7), it is concluded that the S-->Au dative bonding results in evidently different transition characteristics from the S-Au covalent bonding in the Au(I) thioether/thiolate complexes.