Syntheses, structures, and photophysical properties of mono- and dinuclear sulfur-rich gold(I) complexes

The dinuclear gold complexes [{Au(PPh3)}2(µ-dmid)] (1) (dmid) 1,3-dithiole-2-one-4,5-dithiolate) and [{Au(PPh3)}2(µ-dddt)] (2) (dddt) 5,6-dihydro-1,4-dithiine-2,3-dithiolate) were synthesized and characterized by X-ray crystallography. Both complexes exhibit intramolecular aurophilic interactions with Au · · · Au distances of 3.1984(10) Å for1and 3.1295(11) Å for2. A self-assembly reaction between 4,5-bis(2-hydroxyethylthio)-1,3-dithiole-2-thione ((HOCH2CH2)2dmit) and [AuCl(tht)] affords the complex [AuCl{(HOCH2CH2)2dmit}]2(4), which possesses an antiparallel dimeric arrangement resulting from a short aurophilic contact of 3.078(6) Å. This motif is extended into two dimensions due to intra- and intermolecular hydrogen bonds via the hydroxyethyl groups, giving rise to a supramolecular network. Three compounds were investigated for their rich photophysical properties at 298 and 77 K in 2-MeTHF and in the solid state; [Au2(µ-dmid)(PPh3)2] (1), [Au2(µ-dddt)(PPh3)2] (2), and [AuCl{(HOCH2CH2)2dmit}] (4).1exhibits relatively long-lived LMCT (ligand-to-metal charge transfer) emissions at 298 K in solution (370 nm;τe∼17 ns, where M is a single gold not interacting with the other gold atom; i.e., the fluxional C-SAuPPh3units are away from each other) and in the solid state (410 nm;τe∼70 µs). At 77 K, a new emission band is observed at 685 nm (τe=132µs) and assigned to a LMCT emission where M is representative for two gold atoms interacting together consistent with the presence of Au · · · Au contacts as found in the crystal structure. In solution at 77 K, the LMCT emission is also red-shifted to 550 nm (τe∼139 µs). It is believed to be associated to a given rotamer.2also exhibits LMCT emissions at 380 nm at 298 K in solution and at 470 nm in the solid state.4exhibits X/MLCT emission (halide/metal to ligand charge transfer) where M is a dimer in the solid state with obvious Au · · · Au interactions, resulting in red-shifted emission band, and is a monomer in solution in the 10-5M concentration (i.e., no Au · · · Au interactions) resulting in blue-shifted luminescence. Both fluorescence and phosphorescence are observed for4.