ON THE REACTION OF DIOXOURANIUM(VI) WITH DIETHYLENETRIAMINEPENTAACETIC 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 diox ouranium(VI)/chromium(III)-DTPA molar ratio have been evidenced. The m onomer, uncharged, has also been obtained in the solid state and has b een characterised by IR and thermoanalytical techniques. Complexes of dioxouranium(VI) with DTPA alone were also studied. These were 1:1, wi th a different degree of protonation, or 2:1 metal to ligand molar rat io 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 r ange from 1.2 to 1.8). Tn the case of these fractional values a polyme ric structure may be assumed for the solid compounds.