Solvation of silver ions in mixed methyl cyanide + water and methyl cyanide + methanol systems. Radiation and electron spin resonance study

Abstract

Exposure of solutions of silver perchlorate in methyl cyanide to ⁶⁰Co γ-rays at 77 K gave Ag⁰ centres with a reduced silver hyperfine coupling indicative of electron delocalisation on to solvent molecules. Extra splitting into 9 features separated by 6 G established the presence of four equivalent solvent ligands coordinated via nitrogen. This shows that Ag⁺ is solvated by four MeCN molecules and that electron addition does not cause desolvation at 77 K. A similar pattern of ¹⁴N hyperfine features for the Ag^II centre establishes the presence of four strongly coupled ¹⁴N nuclei and the form of the g and A(¹⁰⁹Ag+¹⁰⁷Ag) hyperfine components showed that a square planar arrangement of ligands was probably achieved at 77 K.

Addition of water or methanol had little effect on the e.s.r. spectra up to ≈ 0.5 mole fraction (MF) of protic solvent, showing that Ag⁺ is solvated preferentially by methyl cyanide. However, in the 0.45–0.90 MF region (D₂O) a new species exhibiting hyperfine coupling to only one ¹⁴N nucleus and a greatly increased ¹⁰⁹Ag/¹⁰⁷Ag hyperfine coupling was detected, whose concentration increased on warming above 77 K. This is thought to be formed from Ag⁺(H₂O)₃(MeCN) ions by loss of water following electron addition. Also, an atom-like Ag⁰ centre was detected in this mole fraction range.

Other species detected by e.s.r. spectroscopy included a species with A(¹⁰⁹Ag)= 180 G, thought to be [Ag—C(Me)N], and a species with A(¹⁰⁹Ag)= 130 G, thought to be [Ag[graphic omitted]CH₂OH]⁺.