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

Abstract

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).

Keywords:

• Aluminum(III)
• Chromium(III)
• DTPA
• Complexes
• Thermal properties
• Thermodynamics

ACKNOWLEDGMENTS

The authors would like to thank Prof. R. Caminiti and Dr. C. Sadun of the University “La Sapienza” of Rome for their helpful in X-ray measurements and data processing.

The National Research Council (CNR) and Ministry of the University and Scientific Technological Research (MURST) of Italy are gratefully acknowledged for financial spport.