Structure and substituent effect on the characteristics of some lanthanide chelates with 3-acetyl-1,5-diarylformazans

ABSTRACT

The ionization constants of a homologous series of 1-[0- carboxyphenyl]-3-acetyl-5-arylformazans have been determined potentiometrically. The substituent effect on the pK values was discussed. Furthermore, the stability constants of the formazan chelates with trivalent La, Gd and Er ions were determined. Linear relation between sigma pK of the formazans and log K of their chelates was established. The chelation affinities of formazans towards La, Gd, Er were discussed in relation to the metal ionic size, basicity and number of donor atoms in the formazan molecule. The 1 2 [M L] solid chelates were isolated and characterized by several techniques as ML HL.nH2O where HL = formazan, M = La, Gd or Er ion and n = 0-6