Luminescent μ-ethynediyl and μ-butadiynediyl binuclear gold(I) complexes: Observation of 3(ππ*) emissions from bridging C n 2- units

Abstract

The synthesis and X-ray structural and spectroscopic characterization for LAuC≡CAuL·4CHCl 3 and LAuC≡C-C≡CAuL·2CH 2Cl 2 (1·4CHCl 3 and 2·2CH 2Cl 2, respectively; L = PCy 3, tricyclohexylphosphine) are reported. The bridging C n 2- units are structurally characterized as acetylene or diacetylene units, with C≡C distances of 1.19(1) and 1.199(8) Å for 1·4CHCl 3 and 2·2CH 2Cl 2, respectively. An important consequence of bonding to Au(I) for the C n 2- moieties is that the lowest-energy electronic excited states, which are essentially acetylenic 3(ππ*) in nature, acquire sufficient allowedness via Au spin-orbit coupling to appear prominently in both electronic absorption and emission spectra. The origin lines for both complexes are well-defined and are observed at 331 and 413 nm for 1 and 2, respectively. Sharp vibronic progressions corresponding to v(C≡C) are observed in both emission and absorption spectra. The acetylenic 3(ππ*) excited state of 2 has a long lifetime (τ 0 = 10.8 μs) in dichloromethane at room temperature and is a powerful reductant (E°[Au 2 +/Au 2*] ≤ -1.85 V vs SSCE).