Despite the rich coordination capabilities of the oxo-carbon rhodizonate anion (C6O62-) which has found analytical applications, such as in Pb detection from gunshot residues (Na-rhodizonate test), and in radionuclide separation applications, such as Ra(II) adsorption, its coordination chemistry has not been explored sufficiently . One of the reasons is the limited solubility of many metal rhodizonate complexes. Another is the limited stability of rhodizonate in water: While alkali metal rhodizonate salts are water soluble, they have very short lifetime in aqueous solutions (~2 hours), limiting detailed metal complexation studies. Na-rhodizonate is not soluble in typical polar organic solvents, such as alcohols, but it is soluble in aqueous/organic mixed solvents. The stability of rhodizonate anion is also improved in aqueous/organic solvent mixtures: Na-rhodizonate was found to be stable at water/acetone 50:50 v/v. Complexation between rhodizonate and several metal cations, was studied by structural and spectroscopic methods. UV-Vis, FT-IR and X-ray diffraction provide useful probes for metal complexation under different conditions. For example the insoluble Pb(II)-rhodizonate complex showed notable changes in rhodizonate C-O and C-C FT-IR stretching frequencies, compared to the FT-IR spectrum of Na-rhodizonate.

Coordination chemistry of the rhodizonate anion: Towards understanding the Na-rhodizonate test for Pb

251st National Meeting (2016)

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