Preparation and electronic structure of substituted aromatic dithiolene complexes of gold (III)

Ab initio calculations on the complex ion bis(benzene-1,2-dithiolato)aurate(III), I, have been performed and show that the two highest occupied MO's have π-fcharacter and correspond to the symmetric and antisymmetric combination of the pure ligand HOMO's with only a very small contribution from gold orbitals. Both ligand and metal orbitals contribute significantly to the LUMO which has σ-character. A series of 10 derivatives of I have been prepared and isolated as tetra-n-butylammonium salts. The electronic spectra of these species show two symmetry-forbidden transitions in good agreement with calculations. A spectrochemical series is proposed and related to the electron-releasing efficiency of the substituents. Comparison of the potentials for the reversible oxidation of the complexes (measured by cyclic voltammetry) with the energy of the lowest lying electronic transition reveals a linear relationship which is discussed in terms of the degree of charge transfer from ligands to metal. Improved synthesis of some of the ligands is reported.