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Constitution, dynamics and structure of binary and ternary actinide complexes
KTH, Superseded Departments, Chemistry.
1999 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Stoichiometry, ligand exchange reactions, coordinationgeometry and stability of complexes of type UO2LpFq(H2O)3-n(p= 1–2,q= 1-3), where L is one of the bidentate ligandspicolinate, oxalate, carbonate or acetate have beeninvestigated using single crystal X-ray diffraction, an arrayof19F-,13C-,17O- and1H-NMR techniques and potentiometric titration usingboth F-and H+selective electrodes. The experiments wereperformed in a 1.00 M NaClO4medium. The equilibrium constants were determinedat 25°C while most of the kinetic experiments were done at- 5°C. The equilibrium constants for the stepwise additionof F-to UO2L and UO2L2indicates that the prior coordination of L toU(VI) has a fairly small effect on the subsequent bonding offluoride, except for a statistical effect determined by thenumber of available coordination sites. This indicates thatternary complexes might be important for the speciation andtransport of hexavalent actinides in ground and surface watersystems. A single crystal structure of UO2(picolinate)F32-has been determined showing the same pentagonalbipyramidal symmetry as in aqueous solution studied by NMR. Theexchangeable donor atoms are situated in a plane perpendicularto the linear uranyl group. The complexes show a variety ofdifferent exchange reactions depending on the ligand used. Ithas been possible to quantify external fluoride and the otherligands exchange reactions as well asintra-molecular reactions. This type of detailedinformation has not been observed in aqueous solution before.Water takes a critical part in the exchange mechanism, and whenit is eliminated from the inner coordination sphere a muchslower kinetics can be observed.19F-NMR has showed to be a powerful technique tostudy these reactions, both because of the sensitivity of thisNMR nucleus and also the possibility to observe reactions wherefluoride is not directly involved in the mechanism. TernaryTh(edta)F1-2and (UO2)2(edta)2F1-4have been investigated using1H and19F-NMR. The fluoride complexation to Cm(III) wasstudied using time resolved fluorescence spectroscopy (TRLFS)and the stability constant for the CmF2+complex was determined at 25°C in 1.0 mNaCl.

Keywords. Ternary complexes, actinides,dioxouranium(VI), curium(III), thorium(IV), ligand exchange,isomers, NMR, potentiometric titrations, aqueous solution,oxalate, picolinate, acetate, EDTA.

Place, publisher, year, edition, pages
Stockholm: Kemi , 1999. , p. 68
Series
TRITA-OOK, ISSN 0348-825X ; 1051
Identifiers
URN: urn:nbn:se:kth:diva-2777OAI: oai:DiVA.org:kth-2777DiVA, id: diva2:8489
Public defence
1999-03-29, 00:00
Note

NR 20140805

Available from: 2000-01-01 Created: 2000-01-01 Last updated: 2017-01-20Bibliographically approved

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