Oligomerization of Au(CN)(2)(-) and Ag(CN)(2)(-) ions in solution via ground-state aurophilic and argentophilic bonding

Dicyanoaurate(I) and dicyanoargentate(I) ions undergo significant oligomeri zation in aqueous and methanolic solutions. The absorption edges of K[Au(CN )(2)] and K[Ag(CN)(2)] solutions undergo progressive red shifts with an inc rease in concentration up to near the saturation limits, whereupon total re d shifts of 13.3 x 10(3) and 11.9 x 10(3) cm(-1) are obtained from the resp ective maxima of the corresponding lowest energy monomer bands. Two types o f deviations from Beer's law are observed: a negative deviation for the mon omers' MLCT bands and a positive deviation for the oligomers' bands. Increa sing the concentration within a given concentration range leads to red shif ts in the oligomers' absorption and/or excitation bands dominant in that ra nge, while further increases in concentration lead to die appearance of new lower energy bands. Electronic structure calculations suggest that this be havior is attributed to metal-metal interactions between neighboring Au(CN) (2)(-) or Ag(CN)(2)(-) ions. Formation constants of 1.50 +/- 0.05 and 17.9 +/- 2.0 M-1 are obtained for [Ag(CN)(2)(-)](2) and [Au(CN)(2)(-)](2) dimers , respectively, at ambient temperature.