METAL EXTRACTION BY ALKYL SUBSTITUTED DIPHOSPHONIC ACIDS. PART 2. P,P’-DI(2-ETHYLHEXYL) ETHANEDIPHOSPHONIC ACID AGGREGATION AND IR STUDY*

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Abstract
The complexation and aggregation behavior of P,P′-di(2-elhylhexyl) ethanediphosphonic acid, H2DEH[EDP], a novel solvent extraction reagent for metal ions, was investigated. The aggregation of H2 DEH[EDP] was studied in toluene at 25 °C by vapor pressure osmometry. H2 DEH[EDP] was found to be hexameric in the concentration range 0.2 -0.005 m. 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 H2 DEH[EDP] exists in toluene as a cyclic hexamer similar to an inverted micelle with a large hydrophilic cavity. Ca(II), Ba(II), Eu(m), Fe(UJ), Th(IV) and U(VI) salts of H2 DEH[EDP] were also investigated. The infrared spectra of these compounds reveal that the asymmetric, VASYM(POO−), and symmetric, VASYM (POO−), phosphorus-oxygen stretching modes of the ligand are sensitive to the metal ion present. The shift of both VASYM (POO−) and VASYM (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 (A v) between the two frequencies, i.e. [ VASYM POO′) - VASYM (POO−)], becomes smaller as the ionic potential of the metal ion increases.