An electron spin resonance and optical study of the behaviour of Cs2[TcNCl5] in hydrochloric acid solutions

Abstract

Optical spectroscopy, magnetic susceptibility, and e.s.r. have been used to study the behaviour of Cs₂[TcNCl₅] in aqueous HCl solutions. In 5.6 mol dm^–3 HCl the predominant species is the [TcNCl₄]^– anion (λ_max 398 nm, ε 440 m² mol^–1) possibly with H₂O weakly bound trans to the N atom. Addition of 1 volume of H₂O to Cs₂[TcNCl₅] followed by 2 volumes of 5 mol dm^–3 HCl gives a deep blue species (λ_max. 558 nm, ε 393 m² mol^–1), which is converted to [TcNCl₄]^– on standing. Cs₂[TcNCl₅] dissolved in 0.5 mol dm^–3 HCl gives a pink solution (λ_max. 540 nm, ε 215 m² mol^–1) which is stable over several days. The magnetic susceptibility and e.s.r. measurements indicate that the blue and pink species are diamagnetic. Possible structures of the diamagnetic species are discussed by analogy to the behaviour of [MOX₅]^n– in solutions of varying acidity.