Near-ir spectroscopic study of platinum(II) chelates with 2-aminobenzenethiol and its derivatives in aqueous micellar solutions and its application to the determination of trace platinum(II) ion

Halogeno derivatives of 2-aminobenzenethiol (ABT), 4-chloro-2-aminobenzenethiol (4-ClABT), 5-chloro-2-aminobenzenethiol (5-ClABT) and 4-bromo-2-aminobenzenethiol (4-BrABT) react with platinum(II) ion in aqueous Triton X-100 micellar solutions to form stable near-IR absorbing 1: 2 complexes with a molar absorptivity, ε, of 7 to 8 × 10⁴ M^-1 cm^-1, in the presence of iodine (1.0 x 10^-4 M). As compared with the platinum(II)-ABT complex (ε = 5.8 × 10⁴ M^-1 cm^-1 at 735 nm), the absorption maxima (λ_max) of these ABT derivative complexes shift to longer wavelengths with increased molar absorptivities; the platinum(II)-4-BrABT complex has a value of ε = 7.5 × 10⁴ M^-1 cm^-1 at 759 nm. Consequently, the introduction of electron-withdrawing groups to the 4th position of the ABT ligand as near-IR colorimetric reagents is of great advantage to the trace analysis of platinum(II) ion.