Novel luminescent polynuclear gold(I) phosphine complexes. Synthesis, spectroscopy, and X-ray crystal structure of [Au3(dmmp)2]3+[dmmp = bis(dimethylphosphinomethyl)methylphosphine]

Reaction of K[AuCl4] with bis(dimethylphosphinomethyl)methylphosphine (dmmp) in the presence of thiodiglycol (2,2′-thiodiethanol) in methanol yielded [Au3(dmmp)2]3+, which was isolated as its perchlorate salt. The X-ray crystal structure of [Au3(dmmp)2][ClO4]3 has been determined: monoclinic, space group P21/n, a= 1 2.880(3), b= 14.210(1), c= 21.208(2)A, β= 106.25(1)°, Z= 4, R= 0.047 for 2 927 observed Mo-Kα data. The Au–Au–Au bond angle of 136.26(4)° is greatly distorted from rectilinear geometry, with intramolecular Au ⋯ Au distances of 2.981 (1) and 2.962(1)A. Excitation of a degassed acetonitrile solution of [Au3(dmmp)2]3+ at 300–370 nm resulted in dual phosphorescence (λ= 467 nm, τ0= 1.6 ± 0.2 µs; λ= 580 nm, τ0= 7.0 ± 0.5 µs). A comparison between the electronic absorption and emission spectra of [Au3(dmmp)2]3+ and [Au2(dmpm)2]2+[[dmpm = bis(dimethylphosphino)methane] has been made. The assignment of the lowest electronic excited state in the (P2Au)n system has been suggested to be 3[(dδ*)(pσ)]. The excited-state redox potentials of [Au3(dmmp)2]3+* and [Au2(dmpm)2]2+* have been determined through oxidative quenching experiments with a series of pyridinium acceptors of variable reduction potential.