Metal extraction by alkyl substituted diphosphonic acids .2. P,P'-di(2-ethylhexyl) ethanediphosphonic acid aggregation and IR study

The complexation and aggregation behavior of P,P'-di(2-ethylhexyl) ethanediphosphonic acid, H2DEH[EDP], a novel solvent extraction reagent for metal ions, was investigated. The aggregation of H2DEH[EDP] was studied in toluene at 25 degrees C by vapor pressure osmometry. H2DEH[EDP] was found to be hexameric in the concentration range 0.2-0.005 (m) under bar. Metal ions introduced into the organic phase were shown to have little effect on the aggregation of the extractant. The infrared spectra of metal containing solutions of the extractant and that of the ligand itself suggest that H2DEH[EDP] exists in toluene as a cyclic hexamer similar to an inverted micelle with a large hydrophilic cavity. Ca(Il), Ba(II), Eu(III), Fe(III), Th(IV) and U(VI) salts of H2DEH[EDP] were also investigated. The infrared spectra of these compounds reveal that the asymmetric, nu(asym)(POO-), and symmetric, nu(sym)(POO-), phosphorus-oxygen stretching modes of the ligand are sensitive to the metal ion present. The shift of both nu(asym)(POO- and nu(sym)(POO-) to lower frequencies relative to their values in the sodium salt indicates symmetrical coordination of the phosphonate groups through chelate and/or bridging interactions. The difference (Delta nu) between the two frequencies, i.e. [nu(asym)(POO-)-nu(sym)(POO-)], becomes smaller as the ionic potential of the metal ion increases.