Diphosphines and pyrazole/pyrazolate-type ligands as building blocks in luminescent Au(I) complexes

A series of gold(I) complexes containing diphenylphosphine bridging ligands, dppm, dppe, dpephos, dbfphos and biphep and co-ligands of the type pyrazole have been synthesized. The X-ray crystal structures of [Au2(μ-dpephos)(μ-pz2CH3)][PF6], [Au2(μ-dbfphos)(μ-pz2CH3)][PF6], and of the starting compound [Au2Cl2(μ-biphep)] indicate that the structural and stoichiometric characteristics of the new complexes depend on the diphosphine ligand. The three complexes show Au⋯Au contacts between 3.27 Å and 3.30 Å, with that of the biphep compound being the shortest. Digold (I)-diphosphine derivatives with a bridging pyrazolate ligand are obtained in all cases, except when [Au2Cl2(μ-biphep)] is used as starting material. Surprisingly, in this case, two monodentate neutral pyrazole ligands are attached to the gold atoms. The new complexes are luminescent in the solid state at 77 K and in solution both at room temperature and 77 K. Low energy emission bands related to the presence of Au⋯Au interactions have been identified in some of the compounds in the solid state and/or in solution.