Synthesis, structure, luminescence, and Raman-determined excited state distortions of a trinuclear gold(I) phosphine thiolate complex

The synthesis, crystal structure and spectroscopic properties of a new luminescent trinuclear gold complex, bis(triethylphosphine)gold(I) [mu-(1,1-dicyanoethylene-2,2-dithiolato-1 kappa S:2 kappa S')][mu-(1,1-dicyanoethylene-2,2-dithilato-2 kappa S2:3 kappa S')] (triethylphosphine-1 kappa P)(triethylphosphine-3 kappa P)triaurate(I), 1, are reported. The structure contains a linear array of three gold atoms, the central gold on an inversion center. 1 crystallizes in the P2(1)/n space group with a = 13.681(1) Angstrom, b = 11.433(1) Angstrom, c = 15.608(1) Angstrom, beta = 106.93(1)degrees, V = 2335.4(3) Angstrom(3), and Z = 2. The luminescence spectrum is centered at 19 600 cm(-1) and displays poorly resolved vibronic structure with a spacing of 470 cm(-1), characteristic of a normal mode primarily Au-S in character. The transition is assigned to a dithiolate to gold charge transfer. The vibrational frequencies and intensities obtained from the preresonance Raman spectra are used to calculate the distortions the molecule undergoes when excited to its emissive charge transfer excited state. The largest distortions are along the C=C normal mode centered on the dithiolate ligand and along the Au-S stretching coordinate. These distortions assist in making the charge transfer assignment as dithiolate to gold. The analysis of the emission spectrum and the preresonance Raman spectrum using the time-dependent theory of electronic spectroscopy is discussed.