Co-ordination and conformational isomerism in bis(tricyclohexylphosphine) gold(I) halides

Solid state complexes of bis(tricyclohexylphosphine)gold(I) with halide cou nter ions, Au(PCy3)(2)X (X = Cl, Br or I), have been crystallised from solu tions of[NBu4][AuX2] and PCy3 in dimethylformamide and characterised by sin gle crystal structure determinations, far-infrared spectroscopy and solid s tate P-31 CP MAS NMR spectroscopy. The results show the complexes crystalli se as a unique array of co-ordination and conformational isomers which refl ect the conformational flexibility of the tricyclohexylphosphine ligand and the relative preferences of the halide anions for C-H ... X- versus Au+ .. . X- bonding interactions. The chloride crystallises as a single ionic comp lex, [Au(PCy3)(2)]Cl-+(-), with the gold two-co-ordinate and the cations an d anions well separated in the crystal lattice. The bromide crystallises as three different polymorphs with four distinct molecular structures. The fi rst (alpha) form crystallises as ionic [Au(PCy3)(2)]Br-+(-) with the bromid e adjacent to but not co-ordinated to the gold. The second (beta) form pres ents two crystallographically independent [Au(PCy3)(2)Br] molecules with se mi-co-ordinated bromide and significant differences in the conformational d ispositions of the PCy3 ligands. The third (gamma) form crystallises as [Au (PCy3)(2)Br] with fully co-ordinated bromide. The iodide crystallises with semi-co-ordinated and co-ordinated iodide in [Au(PCy3)(2)I]. PCy3 and [Au(P Cy3)(2)I] complexes respectively. The study provides an unusual series of m olecular 'vignettes' in which the response of the [Au(PCy3)(2)](+) cation t o halide anion can be monitored as it passes through the ligand substituent s and co-ordinates to the central gold atom.