Coordination chemistry of UO/sub 2//sup 2+/ and VO/sup 2+/ in KSCN-KF ionic melts

Journal Article · Wed Apr 20 04:00:00 EDT 1988 · Inorg. Chem.; (United States)

DOI:https://doi.org/10.1021/ic00281a010· OSTI ID:5832779

Jarring, K; Holmberg, B

The stepwise complexation of fluoride ions with UO/sub 2//sup 2+/ and VO/sup 2+/ in molten KSCN has been investigated at 185/degree/C. Fluoride activities were measured in systems (K/sup +/, UO/sub 2//sup 2+/)-(SCN/sup /minus//, F/sup /minus//) and (K/sup +/, VO/sup 2+/)-(SCN/sup /minus//, F/sup /minus//) by a recently developed potentiometric method utilizing a fluoride-selective membrane electrode. Average ligand numbers from 0 to 4.9 and from 0 to 3.8 were established for the uranyl(VI) and vanadyl(IV) systems, respectively. Higher ligand numbers cannot be achieved due to precipitation of K/sub 3/UO/sub 2/F/sub 5/ and K/sub 3/VOF/sub 5/. Stability constants for five consecutive steps for uranyl(VI) and four consecutive steps for vanadyl(IV) have been determined. A specific interaction energy parameter, /Delta/A/sub j/, for each step of ligand exchange of thiocyanate for fluoride is determined. For VO/sup 2+/ the overall fluoride complexation is well described by one single parameter: /Delta/A = /minus/39.6 kJ /times/ mol/sup /minus/1/, independent of j for 1 /le/ j /le/ 4. For UO/sub 2//sup 2+/ a slight increase in /delta/A/sub j/ with increasing j is ascribed to increasing electrostatic repulsion in the equatorial plane of the O-U-O moiety. Changes in hard-sphere Coulomb interaction energies can qualitatively explain the stability sequence Co/sup 2+/ < Cr/sup 3+/ < VO/sup 2+/ < UO/sup 2//sup 2+/ for fluoride complexes in molten KSCN only if formal charges higher than +3.0 and +3.5 are assigned to V and U in VO/sup 2+/ and UO/sub 2//sup 2+/, respectively. Differences in standard free energy change for the substitution of SCN and F between aqueous solution (298 K) and KSCN-KF melt (458 K) for these four acceptors are found to be remarkably constant, 29 kJ /times/ (mol F)/sup /minus/1/, irrespective of central ion and j for J = 1 and 2. 57 refs., 5 figs., 1 tab.

• Research Organization: Univ. of Lund (Sweden)
• OSTI ID: 5832779
• Journal Information: Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 27:8; ISSN INOCA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400201* -- Chemical &amp; Physicochemical Properties
400702 -- Radiochemistry &amp; Nuclear Chemistry-- Properties of Radioactive Materials
ACTINIDE COMPOUNDS
ALKALI METAL COMPOUNDS
ANTITHYROID DRUGS
CARBONIC ACID DERIVATIVES
CHEMICAL REACTIONS
DATA
DRUGS
EXPERIMENTAL DATA
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
HORMONE ANTAGONISTS
INFORMATION
MOLTEN SALTS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
OXYGEN COMPOUNDS
POTASSIUM COMPOUNDS
POTASSIUM FLUORIDES
SALTS
THIOCYANATES
TRANSITION ELEMENT COMPOUNDS
URANIUM COMPOUNDS
URANYL COMPOUNDS
VANADIUM COMPOUNDS