Metal-metal and ligand-ligand interactions in gold poly-yne systems

The acetylide-functionalised thiophene gold(i) complexes [(PPh ₃)Au(C≡C(C₄H₂S)(C₄H ₃S))] 1, [(PPh₃)Au(C≡C(C₄H ₂S)C≡C)Au(PPh₃)] 2, [(PR₃) Au(C≡C(C₄H₂S)₂C≡C)Au(PR ₃)] (R = Ph 3, Cy 4) and [(PPh₃)Au(CC(C₄H ₂S)₃CC)Au(PPh₃)] 5 have been prepared by the reaction of the trimethylsilylethynyl oligothiophene with KOH/MeOH, followed by the addition of a stoichiometric amount of the gold(i) phosphine chloride and NaOMe in MeOH. The products have been characterised spectroscopically and their single crystal X-ray structures determined. In the molecular structures of all the complexes the Au(i) centres adopt the expected linear, two-coordinate geometry, except that in 2 the material forms a polymer through additional Au⋯Au interactions [Au⋯Au 3.2915(10) and 3.2347(9) Å] between the molecular units. With the longer acetylene-functionalised spacer groups no Au⋯Au interactions are present, but hydrogen bonding and π⋯π interactions are of significance. The solution absorption and emission spectra of these complexes have been recorded and the maxima are increasingly red-shifted as the length and planarity of the functionalised spacer groups increases which is consistent with the absorptions and emissions being dominated by ligand-centred π-π* transitions.