AROMATIC 1,2-DITHIOLS AND 1,2-DIAMINES AS CHROMOGENIC REAGENTS FOR NICKEL, PALLADIUM AND PLATINUM IN NEAR-INFRARED SPECTROPHOTOMETRY

The near-infrared (NIR) color forming reagents are described for Ni, Pd, and Pt ions, pi-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, lambda=878 nm (epsilon=1.49X10(4) M-1 cm-1); Pd-tcbt, lambda=1125 nm (epsilon=2.00X10(4)); Pt-tcbt, lambda=880 nm (epsilon=1.92X10(4)), 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 epsilon values are obtained: Pd-Br2dab, lambda=828 nm (epsilon=4.54X10(4)); Pt-Br2dab, lambda=738 nm (epsilon=1.29X10(5)), 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.