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

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(beta(1)/dm(3) mol(-1)) and log(beta(2)/dm(6) mol(-2)) values of 8.12 +/- 0.20 and 17.06 +/- 0.11, respectively, when M2+ = Co?(2+) 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(beta(3)/dm(9) 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-).