Gold bromide complexes in acidic aqueous solutions from 25� to 300�C. A laser raman spectroscopic study

Abstract

Raman spectra of gold bromide complexes in acidic solutions (pH=−0.3–3) have been recorded at 25° to 300°C and at pressures on the liquid vapor curve for the system. At 25°C, only the square planar Au(III) bromide complex, AuBr 4 − , is present in solution with bands at approximately 105, 197 and 215 cm−1. However, in these acidic solutions, when the temperature is 50°C or higher, the square planar Au(III) bromide complex is partially transformed into the linear Au(I) bromide complex, AuBr 2 − , with a single band near 208 cm−1. The transformation of the Au(III) square planar tetrabromo complex into the Au(I) linear dibromo complex is also favored by a reduction of the oxygen fugacity and an increase in pH.