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

The acetylide-functionalised thiophene gold(I) complexes [(PPh3)Au(C=C(C4H2S)(C4H3S))] 1, [(PPh3)Au(C=C(C4H2S)C=C)Au(PPh3)] 2, [(PR3)Au(C=C(C4H2S)(2)C=C)Au(PR3)] (R = Ph 3, Cy 4) and [(PPh3)Au(C=C(C4H2S)(3)C=C)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) Angstrom] between the molecular units. With the longer acetylene-functionalised spacer groups no Au...Au interactions are present, but hydrogen bonding and pi...pi 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 pi-pi* transitions.