Synthetic and structural investigation of new Au(i) complexes featuring bidentate imidazole-2-thione ligands

Gold(i) imidazole-2-thione (IMT) complexes [Au(IMT)₂]⁺, [Au(diIMT)]⁺ and [Au₂(diIMT)₂]²⁺ were synthesized by reacting Au(SMe₂)Cl with ligands containing one or two IMT groups. These Au^I-IMT complexes were characterized by X-ray diffraction, NMR spectroscopy, and mass spectrometry. The IMT ligands provided a linear coordination array around the Au^I center, with IMT C = S bonds orthogonal to the S-Au-S axis. In some cases for complexes of form [Au(IMT)₂]⁺ or [Au(diIMT)]⁺, the cations aggregate to create dimeric or trimeric units in the solid state, and exhibit inter-cation Au⋯Au distances in the range of ∼3.03-3.07 Å, indicative of aurophilic interactions. The new Au^I-IMT complexes exhibit NMR and mass spectra that are generally consistent with the structures of cations of the form [Au(IMT)₂]⁺, [Au(diIMT)]⁺ or [Au₂(diIMT)₂]²⁺ as seen in the solid state. In two cases, however, ¹H NMR spectra suggested that mononuclear and dinuclear complexes [Au(diIMT)]⁺ and [Au₂(diIMT)₂]²⁺ existed in equilibrium, undergoing exchange reactions rapidly on the NMR timescale. Density functional theory (DFT) analysis supported the experimental conformations, showing agreement between the energetically favorable conformers and experimental structures. Photochemical and electrochemical properties were reported, with only one complex being strongly luminescent. The luminescence, at least in solution, did not appear to result from aurophilic interactions.