Electrospray ionization mass spectra of the reactions of NaAuBr_4 and related aurates with nucleophiles

摘要

Electrospray ionization mass spectra in the negative ion mode, ESI(-)MS, of aqueous solutions of AuBr3 at different pH values have been reported by us, confirming the rapid equilibria (speciation) that were observed by spectrophotometry: AuBr_4~- and [AuBr_3 (OH)]~- predominate at pH4 and [AuBr_2(OH)_2]~- in neutral solutions. Independently, other authors have reported similar ESI mass spectra of [AuCl_n(OH)_(4-n)]~-. Thus, gold seems to be unique among all the elements of the periodic table, not only because of the properties of the metal, known fromthe beginning of themankind, and of the gold nanoparticles, but also because gold(III) salts do not precipitate easily Au(OH)_3 under neutralization, particularly in the presence of anions such as bromide or cyanide. With the aim of uncovering further features of aurate(III) ions, we carried out a series of MS experiments that are reported for the first time: (1) the characterization of commercially available samples of NaAuBr_4 and NaAuCl_4 at different pH values, (2) the detection by ESI(-)MS of the exchanges of ligands (Cl/Br/CN) in aurates and (c) a study of the reactivity (or lack of reactivity) of NaAuBr_4 with alcohols, phenols, carbonyl compounds, 1,3-dicarbonyl or 1,3-dicarboxyl compounds, and oximes, also followed by ESI(-)MS.