Complexation of zinc(II) and other divalent metal ions by the fluorophore 2-methyl-8-(toluene-p-sulfonamido)-6-quinolyloxyacetic acid in 50% aqueous ethanol

Abstract

A potentiometric and fluorescence study of the complexation of divalent metal ions (M²⁺) by the fluorophore 2-methyl-8-(toluene-p-sulfonamido)-6-quinolyloxyacetic acid (H₂L) in 50% (v/v) aqueous ethanol at 298.2 K and I = 0.10 mol dm^–3 (NaClO₄) showed that the [ML] and [ML₂]^2– complexes are characterised by log(β₁/dm³ mol^–1) and log(β₂/dm⁶ mol^–2) values of 8.12 ± 0.20 and 17.06 ± 0.11, respectively, when M²⁺ = Co²⁺ and corresponding values of < 8 and 15.73 ± 0.03 when M²⁺ = Ni²⁺, 11.96 ± 0.02 and 21.40 ± 0.03 when M²⁺ = Cu²⁺, 9.65 ± 0.02 and 19.11 ± 0.06 when M²⁺ = Zn²⁺ and 8.44 ± 0.50 and 15.38 ± 0.40 when M²⁺ = Cd²⁺. In the cobalt(II) system, [CoL₃]^4–, where log(β₃/dm⁹ mol^–3) = 25.56 ± 0.11, was also detected. The pK_a values for H₃L⁺ are 1.87 ± 0.10, 3.72 ± 0.03 and 10.01 ± 0.02. These data are discussed together with the fluorescence characteristics of HL^–, [ZnL] and [ZnL₂]^2–.