Aromatic 1, 2-Dithiols and 1, 2-Diamines as Chromogenic Reagents for Nickel, Palladium and Platinum in Near-Infrared Spectrophotometry

Abstract

The near-infrared (NIR) color forming reagents are described for Ni, Pd, and Pt ions, π-electron conjugated 1, 2-dithiols and 1, 2-diamines. The dithiol ligands forms the yellow 1:2 chelates with these metal ions and subsequent oxidation with I₂ or IO₃^- ion yields the corresponding NIR active species. The spectroscopic data are: Ni-tcbt, λ=878nm (ε=1.49×10⁴M^-1 cm^-1); Pd-tcbt, λ=1125nm (ε=2.00×10⁴); Pt-tcbt, λ=880nm (ε=1.92×10⁴), where tcbt means 3, 4, 5, 6-
tetrachlorobenzene-1, 2-dithiol. In contrast with the dithiolato chelates, the complexation and oxidation processes for metal-diamine systems are concurrently accomplished under slightly acidic (for Pt ion) or slightly alkaline (for Pd ion) conditions, respectively. Very large E values are obtained: Pd-Br₂dab, λ=828nm (ε=4.54×10⁴); Pt-Br₂dab, λ=738nm (ε=1.29×10⁵), where Br₂dab denotes 3, 5-dibromo-1, 2-diaminobenzene. A new idea for designing unique NIR color formation systems is reported; the complexation reactions must be linked with reduction-oxidation processes. The satisfactory selectivity of the Br₂dab system for Pt in the presence of iron, copper, and zinc ions is demonstrated for Pt determination in possible clinical practices.