Solvation spectra. Part 52.—The aquation of silver atoms and cations: a radiation and electron spin resonance study

Abstract

Exposure of a range of aqueous solutions containing Ag^I cations to ⁶⁰Co γ-rays at 77 K gave Ag^II and Ag^O together with other paramagnetic products. The Ag^II centres have [graphic omitted] configurations, which means that linear solvation for Ag⁺ is unlikely, since this would lead to a [graphic omitted] configuration. A range of distinct Ag^O centres displaying low (∼80 %) atom character was detected. Their yield was enhanced, but their distribution largely unaltered, when certain additives, such as potassium fluoride, were used to give glassy solids. However, their distribution varied with dose and with temperature. The major initial product exhibited an extra 6 G doublet splitting due to hyperfine coupling to a single proton. On further irradiation, this centre was superceded by others exhibiting no resolved coupling to protons but, in some cases, well defined g and A anisotropy. For all the Ag^O centres, g_av was less than the free-spin value. When water enriched in ¹⁷O was used, superhyperfine coupling was detected for some of the Ag^O centres. From the apparent anisotropic and isotropic coupling constants, delocalisation of ∼5% per water molecule was deduced. The intensities indicated the presence of several equivalent water ligands but solvation numbers could not be derived accurately.

These results for Ag^O are significant for two reasons; (1) they show that solvation is not lost in aqueous glasses when the charge on an ion is neutralised. This contrasts with the fact that when small neutral molecules become charged, solvation is acquired, even at 77 K. (2) They indicate the presence of a range of discrete Ag^I solvates in solution rather than a single preferred unit.