SOLUTION STABILITIES OF SOME MIXED-LIGAND COMPLEXES OF UO22+ AND TH-4+ WITH COMPLEXONES AND SALICYLIC ACIDS

Formation constants (log K(MAI)MA) of mixed ligand complexes (MAL), where M = UO2(2+) or Th4+, A = IMDA, NTA, HEDTA, EDTA, CDTA or DTPA, L = salicylic acid (SA) or 5 - sulphosalicylic acid (SSA), have been determined by pH titrations using Irving - Rossotti approach at 25-degrees-C and at I = 0.2 (mol dm-3, KNO3). The solution stabilities exhibit the sequence (i) Th4+ > UO2(2+), (ii) IMDA > NTA > HEDTA > EDTA > CDTA > DTPA, and (iii) SA > SSA with respect to metal ions, primary ligands and secondary ligands, respectively. The formation constants log K(ML)M and log K(ML2)ML have also been determined. The DELTA-log K values have been found to be negative-increasing numerically with the negative charge on the deprotonated primary ligand (A(n-)).