3-Deoxy-D-erythro-hexos-2-ulose bis(thiosemicarbazone) copper(II) chelate. Studies in solution and in the solid state

The 3-deoxy-D-erythro-hexos-2-ulose bis(thiosemicarbazone) (LH2) acts as a tetradentate ligand with S2N2 donor sites to form a copper(II) chelate (Cu(II)L). The Cu K-edge X-ray absorption spectra analysis of a powdered sample revealed a square-planar S2N2 local coordination geometry with average Cu-N and Cu-S distances of 1.92 and 2.33 Angstrom. The EXAFS and XANES spectra and the structural parameters of a DMF solution sample indicate the retention of the square-planar local structure of the Cu(II)S2N2 chromophore upon dissolution. Semiempirical PM3 calculations indicate that the structure of Cu(II)L with the copper(II) ion bound to the S2N2 donor set disposed in a square-planar geometry is the most favorable one (with the highest \Delta H-f\). The formation constant (log K-f = 20.65 +/- 0.06) of the neutral [CuL] species was calculated in 30% v/v dioxane-water and the protonation and deprotonation constants determined.