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 for 1 and 3.1295(11) Å for 2. A self-assembly reaction between 4,5-bis(2-hydroxyethylthio)-1,3-dithiole-2-thione ((HOCH 2 CH 2 ) 2 dmit) and [AuCl(tht)] affords the complex [AuCl{(HOCH 2 CH 2 ) 2 dmit}]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{(HOCH 2 CH 2 ) 2 dmit}] (4). 1 exhibits 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-SAuPPh3 units 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 = 132 μs) 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. 2 also exhibits LMCT emissions at 380 nm at 298 K in solution and at 470 nm in the solid state. 4 exhibits 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 10−5 M concentration (i.e., no Au···Au interactions) resulting in blue-shifted luminescence. Both fluorescence and phosphorescence are observed for 4.