Solvation of exchangeable cations in sulfonated polystyrene ion-exchange resins: An ESR study

The solvation of Cu²⁺ ions in sulfonated poly(styrene-co-divinylbenzene) ion-exchange resins has been studied by electron spin resonance (ESR) spectroscopy. The ESR spectrum of Cu²⁺ ions in hydrated resins is characteristic of the freely tumbling hexahydrated cation. On dehydration of the gel, the spectrum gradually broadens suggesting that dehydration occurs in a relatively disordered way. Reversible loss of ESR signal intensity is attributed to dipolar interactions between neighbouring Cu²⁺ ions. In resins fully solvated with methanol, the ESR spectrum is characteristic of the unconstrained, fully solvated Cu²⁺ ion and, again, on drying, loss of solvent occurs without the formation of any well-defined Cu²⁺ centres. Similar behaviour is seen for resins solvated with i-propanol and n-butanol.