BINUCLEAR CHELATES OF DTPA WITH ALUMINUM(III) AND CHROMIUM(III) IONS

The reaction of aluminum(III) with chromium(III)-DTPA “complex chelating agent” has been investigated, in aqueous solution, at 20°C in NaClO4 1.0 mol dm-3 by potentiometric methods. In acidic medium and with ligand excess three different complex species (AlCrL+, Al(OH)CrL and Al(CrL)-2) were evidenced and, knowing the protonation constants of the chromium(III)-DTPA complex, the stability constants were calculated. The comparison of these constants with those of the corresponding complexes of aluminium(III) with iminodiacetic acid proved the coordination of aluminum(III) occurs in all cases by iminodiacetic groups. The mononuclear [H2AlL (H2O)] and the heterobinuclear [Al(OH)CrL(H2O)6] complexes were also obtained as solid compounds and were characterized by X-ray and IR spectroscopy and thermoanalytical techniques (TG and DSC).