In Situ IR Study of the Anodic Polarization of Gold Electrodes in Polar Aprotic Solvents: DMSO and DMF Solutions of Cyanate, Thiocyanate and Selenocyanate Ions

Abstract

Subtractively normalised Fourier transform infrared spectroscopic (SNIFTIRS) studies combined with volammetric and supporting model solution studies have conclusively shown that Au electrodes anodically polarized in DMSO and DMF solutions containing the pseudohalide ions: cyanate, thiocyanate and selenocyanate with tetrabutylammonium perchlorate as supporting electrolyte dissolve to form Au(I) pseudohalide complex ions (i.e. [Au(NCO)₂]⁻, [Au(SCN)₂]⁻ and [Au(SeCN)₂]⁻. This work has demonstrated the significance of the Au(I) oxidation state which occurs after applied voltages of +500 mV(AgCl/Ag) in the little characterized electrochemistry of this metal in polar aprotic solvents, DMSO and DMF The Au(I) species observed electrochemically by SNIFTIRS were confirmed by independent preparation in DMSO/DMF containing mixtures of KAuBr₄ and the pseudohalide salt (KOCN/NaSCN/KSeCN) and exploiting fortuitous redox chemistry where Au(I) formed spontaneously. The model solutions examined by transmission FTIR and ESI-MS confirmed the existence of the Au(I) species posited in the SNIFTIRS experiments but additionally revealed other interesting side reactions occurring in the model solutions.