Synthesis of a New Tetrakis(2-pyridinyl)pyrazine Complex of Gold(III) and Its Computational, Spectroscopy and Electrochemical Characterization

The cationic dinuclear (hydroxo)AuIII complex [Au2(OH)2(tppz)]Cl4 [tppz = 2,3,5,6-tetrakis(2-pyridinyl)pyrazine] was prepared by allowing the ligand tppz to react with K[AuCl4]·2H2O in refluxing methanol. Its NMR and IR spectra support the formation of a symmetric hydroxo derivative instead of the expected chloro complex. DFT B3PW91 calculations were performed with various basis sets to give better insights into the properties of the prepared complex and to compare it with the known derivative [Au(OH)(terpy)]2+ (terpy = 2,2′:6′,2″-terpyridine). The electrochemical behaviour of [Au2(OH)2(tppz)]Cl4 was investigated by cyclic voltammetry and it was found that two main irreversible reduction processes occurred. In particular, a four-electron process, leading to the formation of gold(I) complex species in solution, and a two-electron process affording metallic gold were observed. The electronicity involved in the two processes was verified by macroelectrolysis at controlled potential.