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- Author or Editor: A. Saidel x
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Abstract
Thermal gravimetric (TG) and differential thermal (DTA) analyses were performed to characterize the thermal behavior and the stoichiometry of uranyl bis-1,3-diketonate complexes (R1COCR2COR3)2 UO2 x H2O, where R1,3=CH3; C2H5; C6H5; CF3; pNO2−C6H4; pCl−C6H4; pMe−C6H4; NH−C6H5; R2=H, C6H5 andx=1; 2. Based on the data obtained, a thermal degradation mechanism for each complex was proposed. The final degradation product for all studied complexes was U3O8 oxide. The temperature of the first organic fragment rupture including the U-O (ligand) bond was taken as criterion for the thermal stability of the metal-oxygen donor bond in these complexes. The observed stability order is in good agreement with the IR determined constant force values,k, of the U-O (ligand) bond.
31P-NMR study of the organophosphorous complexes of uranium(VI)
I. The intermolecular ligand exchange kinetics in uranyl nitrate complexes with TBP and TOPO
Abstract
The intermolecular ligand exchange in uranyl nitrate complexes with TBP and TOPO is studied by31P-NMR. The constant rates at 25°C in CCl4 are: (8.47±1.86)·103 s–1 for U-TBP and (1.3±0.04)·104M–1·s–1 for U-TOPO system. The very similar activation parameters values of the ligand exchange suggest the same mechanism for both systems, namely an one-step interchange mechanism. The differences between the systems regarding the rate equations and the extraction properties are discussed.
31P-NMR study of the organophosphorous complexes of uranium(VI)
II. The system uranyl nitrate-tri- N -butylphosphate-tri- N -octylphosphine oxide
Abstract
The formation of the mixed complex UO2(TOPO)(TBP)(NO3)2 is reported by31P-NMR spectroscopy for the first time. The extraction of the uranyl nitrate by a TBP and TOPO mixture was simulated in a NMR vial and monitored 
in situ
. The equilibrium constant values of the processes in which the mixed complex is involved, i.e.:K
R
, for the redistribution of TBP and TOPO ligands between their uranyl complexes,K
M
, for the formation from consititutive molecules,K
s
, for the substitution of the uranyl coordinated TBP by TOPO are determined. The redistribution constant,K
r
at 25°C (4.43±0.5) and the changes of the thermodynamic variables 
H (0.59±0.14 kcal/mol).
S (5.04±0.51 cal/mol·degree) have values close to the statistical values, suggesting a random nature of this process. TheK
S
value (4.5·103) reveals the much greater affinity for uranium(VI) of TOPO relative to TBP.
