Solvation of silver ions in a range of binary solvent systems. Radiation and electron spin resonance study

Abstract

Exposure of dilute solutions of silver perchlorate in a range of pure and mixed solvents to ⁶⁰Co γ-rays at 77 K gave Ag⁰ and Ag^II centres with reduced silver hyperfine coupling indicating delocalisation onto solvent molecules. In certain cases this was confirmed by the detection of hyperfine coupling to ligand nuclei. Solvents used included water, methanol, cyanomethane, acetone, methyltetrahydrofuran, dimethyl-sulphoxide, dimethylformamide, ethylamine, triethylamine, pyridine, ammonia, benzene and toluene.

Results for the Ag⁰ centres are interpreted in terms of primary species, which retain the solvation of the original Ag⁺ ions, and secondary centres, which have lost one or more of the primary solvent molecules of the cation, the limiting species being generally the unsolvated atoms. In some cases Ag⁺₂, Ag²⁺₃ and Ag³⁺₄ clusters were also detected either at 77 K or after annealing.

A linear correlation between the isotropic hyperfine coupling to ¹⁰⁹Ag and the solvent donor number was followed by the majority of pure solvents, the most marked exceptions being pyridine and cyanomethane. Reasons for this trend and the exceptions are discussed.

Other species with relatively low isotropic hyperfine coupling to ¹⁰⁹Ag were detected, and possible structures are suggested.