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

The acetylide-functionalised thiophene gold(I) complexes [(PPh₃)Au(CC(C₄H₂S)(C₄H₃S))] 1, [(PPh₃)Au(CC(C₄H₂S)CC)Au(PPh₃)] 2, [(PR₃)Au(CC(C₄H₂S)₂CC)Au(PR₃)] (R = Ph 3, Cy 4) and [(PPh₃)Au(CC(C₄H₂S)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.