THERMODYNAMIC STUDIES ON THE COMPLEXATION OF ALKALINE-EARTH METAL-IONS WITH ORTHO-PHENYLENEDIAMINE-N,N,N',N'-TETRAACETATE IN AQUEOUS-SOLUTIONS

Potentiometric and calorimetric studies were carried out for the complexation of o-phenylenediamine-N,N,N',N'-tetraacetate (PhDTA, L4-) with alkaline-earth metal ions (M2+) in aqueous solutions at 25.0-degrees-C and 1.0 M (NaClO4). The formation constants (log K(ML)) obtained are 6.48 (Be), 6.481 (Mg), 8.27 (Ca), 5.47 (Sr), and 3.99 (Ba), respectively. The changes in enthalpy (DELTA-H-degrees(ML)/kJ mol-1) are 45.5 (Be), 34.3 (Mg), -14.0 (Ca), 2.7 (Sr), and 2.5 (Ba), respectively.