Proton-linked bi- and tri-metallic gold cyanide complexes observed by ESI-MS spectrometry

Electrospray ionization spectra of potential cyanide-containing gold-drug metabolites revealed additional, weak, unanticipated peaks at approximately twice the mass of the gold(I) and gold(III) cyanide complexes. The exact masses correspond to proton-linked bimetallic complexes, [H{Au(CN)m}2]−, (m = 2,4). Further investigation revealed a total of 12 examples, including trimetallic complexes, [H2{Au(CN)m}3]−; mixed species with two complexes, [H{Au(CN)2}{Au(CN)4}]−; and thiolato species, [H{(RS)Au(CN)3}2]−. trans-[AuX2(CN)2Cl2]− and trans-[AuX2(CN)2Br2]− generated 35Cl/37Cl and 79Br/81Br isotopic patterns for the protonated bi- and tri-metallic analogues which were in good agreement with the presence of four or six halide ligands, respectively. Concentration-dependent studies demonstrated that the signals are independent of the solution concentrations of mono-metallic precursors, suggesting formation in the gas phase during or following droplet desolvation.