Nuclear magnetic resonance study of ligand exchange on dioxopentakis(trimethyl phosphate)uranium(VI) ion and its triethyl phosphate analogue
Ligand exchange processes on UO/sub 2/L/sub 5//sup 2 +/ where L is either trimethyl phosphate (TMP) or triethyl phosphate (TEP) have been studied using /sup 1/H and /sup 31/P NMR techniques, respectively. In CD/sub 2/Cl/sub 2/ diluent the rate law for L exchange is rate = 5k/sub ex/ (UO/sub 2/I/sub 5//sup 2 +/), and the exchange mechanism is considered to be either D or I/sub d/. Typical observed rate parameters are k/sub ex/ (260 K) = 95 +- 6 (32.2 +- 2.7) s/sup -1/, ..delta..H/sup double dagger/ = 6.0 +- 0.3 (10.4 +- 0.4) kcal mol/sup -1/, ..delta..S/sup double dagger/ = - 26.1 +- 2.3 (-11.3 +- 1.4) cal deg/sup -1/ mol/sup -1/ for solutions in which (UO/sub 2/L/sub 5//sup 2 +/) = 0.039 (0.139) M, (L) = 0.198 (0.745) M, and (CD/sub 2/Cl/sub 2/) = 12.18 (11.21) M where in each case the first magnitude refers to the TMP system and that in parentheses refers to the TEP system. From a comparison of ..delta..H/sup double dagger//..delta..S/sup double dagger/ linear free energy relationships it is concluded that the surface charge density at the uranium center seen by the equatorial ligands in UO/sub 2/L/sub 5//sup 2 +/ lies between that on the tervalent aluminum and the divalent first-row transition metal centers in AlL/sub 6//sup 3 +/ and ML/sub 6//sup 2 +/, respectively.
- Research Organization:
- Univ. of Adelaide
- OSTI ID:
- 5217808
- Journal Information:
- Inorg. Chem.; (United States), Vol. 16:11
- Country of Publication:
- United States
- Language:
- English
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400702* - Radiochemistry & Nuclear Chemistry- Properties of Radioactive Materials