Stability Constants of Tervalent Rare Earth Metal Complexes with 1,10-Diaza-4,7,13,16-tetraoxacyclooctadecane in Aqueous Sodium Chloride Solutions

摘要

The metal complex stability between tervalent rare earth metal ions (ytterium, praseodymium, europium, gadolinium, holmium and ytterbium) and 1,10-diaza-4,7,13,16-tetraoxacyclooctadecane (kryptofix 22) in aqueous sodium chloride solution was studied by solvent extraction method. The solvent extraction included 2-thenoyltrifluoroacetone as a chelating extractant and carbon tetrachloride as a solvent. The metal extractability in the absence and presence of kryptofix 22 gave a quantitative measure of the stability of metal-kryptofix 22 complexes formed in aqueous solution which were found to be unanimously 1:1 (metal:ligand ratio) in composition. The complex stability constants thus obtained (0.1 M sodium chloride, 298 K) were in the range 109 - 1011, being maximum at gadolinium. The values were discussed in com-parison with those of the related ligand 18-crown-6.