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

Abstract

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)Å, β= 106.25(1)°, Z= 4, R= 0.047 for 2 927 observed Mo-K_α 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)Å. 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[(d_δ*)(p_σ)]. 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.