THE HYDROLYSIS OF GOLD(I) IN AQUEOUS ACETONITRILE SOLUTIONS

The hydrolysis and subsequent decomposition of gold(I) in aqueous solu tions with acetonitrile were found not to yield the expected dispropor tionation products gold(0) and gold(III) in a ratio of 2:1, but more t han 98% gold(0), and also oxygen when acetonitrile from the gold(I) st ock solution was removed first. The pH dependence of the reaction rate is attributed to a hydrolysis equilibrium established before the redo x decomposition. The species [Au(CH3CN)(OH)] and Au(OH) were identifie d by alkalimetric titrations and numerical analysis, with the logarith ms of their formation constants being 10.7 and 10.2 respectively. Thes e species seem to be sources of the OH. radical, which explains the ox ygen formation in the absence of acetonitrile, and an alteration of it s UV spectrum when it is left in the reaction mixture. The high comple x stability of gold(I) with hydroxide ions means that it is one of the most acidic univalent cations, similar to HgCH3+. The known relativis tic contraction of the 6s orbital in gold(I) may account for this unus ual property.