Analytical Sciences

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

Kazuho INABA* and Yoshitaka MASUDA**

*National Institute for Environmental Studies, Onogawa, Tsukuba 305, Japan
**Department of Chemistry, Faculty of Science, Kobe University, Rokkodai, Nada, Kobe 657, Japan

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 chelat-ing 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 10 9 - 10 11 , being maximum at gadolinium. The values were discussed in com-parison with those of the related ligand 18-crown-6. (Keywords: Stability constant, liquid-liquid extraction, masking, rare earth(III), kryptofix 22)

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