Synthesis, characterization and photophysical properties of gold(I)–copper(I) alkynyl clusters with 1,4-bis(diphenylphosphino)butane, effect of the diphosphine ligand on luminescence characteristics

Abstract

Reactions of the {AuC2R}n polymer (R = –C6H4NO2, –C6H5, –C6H4Ph, –C6H4OMe, –C6H4NMe2, –C(OH)Me2, –C6H10(OH)) with stoichiometric amount of 1,4-bis(diphenylphosphino)butane and Cu(I) ions afford the dicationic complexes of general formula [Au6Cu2(C2–R)6(PPh2(CH2)4PPh2)3](PF6)2. The compounds obtained (1–7) display common “rods-in-belt” structural motif with the “Cu2{Au(C2R)2}3” central cluster core wrapped about by the {Au3(Ph2P(CH2)4PPh2)3} belt. This structural pattern was revealed in solid state by X-ray crystallography and confirmed in solution using the NMR spectroscopy. The complexes 6 and 7 containing hydroxyl substituents in the alkynyl ligands demonstrate structural distortions due to hydrogen bonding inside the cluster core. All complexes studied exhibit intense phosphorescence in dichloromethane solution, the characteristics of which depend on donor ability of the alkynyl ligand substituents. Comparison of the emission wavelengths in 1–7 with those observed in the congeners based on the aromatic diphosphine (PPh2C6H4PPh2) showed considerable blue shift of the emission band maxima in the complexes under study. The theoretical DFT calculations indicated that the triplet emission in 1–7 is mainly determined by electron transitions inside the cluster core with some admixture of MLCT character, the contribution of which plays more important role compared to the analogs with aromatic diphosphine and causes the observed hypsochromic shift of emission.