Luminescence of Salicylic Acid in Concentrated Aqueous ZnCl₂ + LiCl Solutions

Abstract

The luminescence of 1.158 × mol dm^-6 solutions of salicylic acid in (1-X)ZnCl₂,4H₂O + XLiCl,4H₂O has been investigated. The luminescence band half-width (Δ_½) and (λ_max)wavelength of maximum intensity (λ_max) have been determined as a function of the relative proportions of the components ZnCl₂,4H₂O and LiCl,4H₂O. Both Δ_½ and λ_max are invariant or almost invariant within experimental precision in the approximate composition regions O ≤ X ≤ 0.4 and 0.6 ≤ X ≤ 1. λ_max shifts to shorter wavelength and Δ_½ decreases sharply, in the approximate composition range 0.4 ≤ X ≤ 0.6.

The results are interpreted as indicating that addition of LiCl,4H₂O to ZnCl₂,4H₂O causes initially depolymerization of species in which both water and chloride are coordinated to zinc, and that replacement of H₂O by Cl- in the primary coordination sphere of zinc begins to occur at about X = 0.4 and is complete at a composition close to that corresponding to the tetrachlorozincate anion stoichiometry.