Structure and dynamics in the complex ion (UO_2)_2(CO_3)(OH)_3~-

摘要

The structure and ligand exchange dynamics of the ternary complex (UO_2)_2(CO_3)(OH)_3~- have been investigated by EXAFS and NMR spectroscopy. Very broad signals can be observed in both the ~(13)C and the ~(17)O NMR spectra. The EXAFS data show the presence of 1.3 +- 0.3 short uranium-oxygen distances at 2.26 A, consistent with single bonded hydroxide and 3.9 +- 0.6 distances at 2.47 A for the other ligands in the first co-ordination shell. There is also evidence for a U…U interaction at 3.90 A. based on the EXAFS and NMR data we suggest the presence of three isomers with different bridge arrangements, the dominant one, C, contains 80% of the uranium and the minor ones A and B, 5 and 15%, respectively. The ligand exchange reactions between these isomers are slow. The NMR data indicate that the main reactions involve intramolecular exchanges between isomers with different positions of the non-bridging ligands in A, B and C. we suggest that these take place through water exchange as discussed earlier for ternary uranium(VI) complex.