Ma. Rawashdeh-omary et al., Oligomerization of Au(CN)(2)(-) and Ag(CN)(2)(-) ions in solution via ground-state aurophilic and argentophilic bonding, J AM CHEM S, 122(42), 2000, pp. 10371-10380
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.