Studies on the complexes of lanthanide ion with multidentate ligand (I)

Log K, ΔH and ΔS for the complexation of La3+, Ce3+ and Eu3+ with various multidentate ligand containing crown ether, diaza crown ether and diamine ether have been determined in methanol and acetonitril solutions at 25deg C by solution calorimetric titration method. The greater stability constant of La3+-15C5 than those of 18C6 diaza [2.2] in methanol are discussed in terms of the size of metal ion and the ligand cavity and of metal ion solvation. The stabilities of Ce3+ and La3+ ion complexes with a various multidentate ligand in acetonitril are in the order of (diamine ether) < 18C6 < 15C5 < diaza [2.1] < diaza [2.2]. This result are discussed in terms of the covalent bonding of -NH group in diaza ligand in addition to the ion-dipole interaction and of the optimum size concept and of the macrocyclic effect. The stability constants of Ce3+, La3+ and Eu3+ -diaza [2.2] complexes in acetonitril are increased with the following order: Eu3+ < La3+ < Ce3+, that is increasing order of the optimum size and of the charge density of metal ion. (Author)