Electrochemistry and Coordination Behaviors of Hypoxanthine-Au(III) Ion in the Cyanide-Free Gold Electrodeposition

Alkaloid hypoxanthine is a novel complexant for green cyanide-free Au(III) electrodeposition. In this work, the electrochemical and coordination behaviors of hypoxanthine-Au(III) ion in the green cyanide-free bath are studied. The electrochemical behavior confirms that hypoxanthine-Au(III) ion is in the irreversible two-step electro-reductions with the first controlled by diffusion and the second by diffusion and electrochemistry. The stability constant of hypoxanthine-Au(III) ion is 4.8 × 1030. DFT calculations further indicate that the optimal coordination structure is N3-Au-N7 with the N-Au average bond energy of 11.03 eV. The bath component of potassium citrate plays almost no influence, whereas the additive of sulfocompounds shows a significant effect on the electro-reduction of hypoxanthine-Au(III) ion. Based on the cyanide-free Au(III) electrodeposition bath, the obtained gold coating is fine and compact in grains without organic inclusion and in the resistivity of 2.84 × 10−8 Ω·m.