On the reaction of dioxouranium(VI) with diethylene triaminepentaacetic acid (DTPA) and with chromium(III)-DTPA chelating agent

Formation of complexes by dioxouranium(VI) with chromium(III)DTPA as "chelating agent" has been investigated, by potentiometry, in aqueous solution. Two chelates, a monomer and a dimer, with the same 1:1 dioxouranium(VI)/chromium(III)-DTPA molar ratio have been evidenced. The monomer, uncharged, has also been obtained in the solid state and has been characterised by IR and thermoanalytical techniques. Complexes of dioxouranium(VI) with DTPA alone were also studied. These were 1:1, with a different degree of protonation, or 2:1 metal to ligand molar ratio and were evidenced in aqueous solution. The stability constants of the above equilibria have been calculated at 20 degrees C, in NaClO4 1.0 mol/dm(3). In the solid state, several compounds were prepared and no stoichiometric metal to ligand molar ratios are found (the values range from 1.2 to 1.8). Tn the case of these fractional values a polymeric structure may be assumed for the solid compounds.