Intensely Luminescent Homoleptic Alkynyl Decanuclear Gold(I) Clusters and Their Cationic Octanuclear Phosphine Derivatives

Treatment of Au(SC4H8)Cl with a stoichiometric amount of hydroxyaliphatic alkyne in the presence of NEt3 results in high-yield self-assembly of homoleptic clusters (AuC2R)(10) (R = 9-fluorenol (1), diphenylmethanol (2), 2,6-dimethyl-4-heptanol (3), 3-methyl-2-butanol (4), 4-methyl-2-pentanol (4), 1-cyclohexanol (6), 2-borneol (7)). The molecular compounds contain an unprecedented catenane metal core with two interlocked 5-membered rings. Reactions of the decanuclear clusters 1-7 with gold-diphosphine complex [Au-2(1,4-PPh2-C6H4-PPh2)(2)](2+) lead to octanuclear cationic derivatives [Au-8(C2R)(6)(PPh2-C6H4-PPh2)(2)](2+) (8-14), which consist of planar tetranuclear units {Au-4(C2R)(4)} coupled with two fragments [AuPPh2-C6H4-PPh2(AuC2R)](+). The titled complexes were characterized by NMR and ESI-MS spectroscopy, and the structures of I, 13, and 14 were determined by single-crystal X-ray diffraction analysis. The luminescence behavior of both Au-10(I) and Au-8(I) families has been studied, revealing efficient room-temperature phosphorescence in solution and in the solid state, with the maximum quantum yield approaching 100% (2 in solution). DFT computational studies showed that in both Au-10(I) and Au-8(I) clusters metal-centered Au --> Au charge transfer transitions mixed with some pi-alkynyl MLCT character play a dominant role in the observed phosphorescence.