Analytical Sciences

Several Factors Influencing the Stability of Extracted Species in Synergistic Extraction of Lanthanide(III) with Pivaloyltrifluoroacetone and 2,2′-Bipyridyl

Tadahisa SAITO, Kazuaki SATO, Mitsunobu MIRATSU, Izuru MATSUBAYASHI, Masayuki INOUE, and Yuko HASEGAWA

Department of Chemistry, Faculty of Science, Science University of Tokyo, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan

The stability constants and the hydration number of a complex between tris(pivaloyltrifluoroacetonato)lanthanide(III) (LnA₃) and 2,2′-bipyridyl (B), LnA₃B, and the complexation heat were determined across the Ln series by a solvent-extraction technique, Karl Fischer coulometry, and calorimetry, successively. The number of water molecules released from LnA₃ upon the complexation with B as well as the values of the stability constant increased along with increasing Ln atomic number to around Dy(III); via a maximum, it decreased. It is concluded that the largest stability constant of the complex of Ho(III) or this vicinity is derived from the strongest bond energy, due to the fitness between LnA₃ and B. This conclusion was supported by the trend of the variation of the entropy change as well as that of the hydration number across the Ln series.

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