Structure and dynamics in the complex ion (UO2)2(CO3)(OH)3–

The structure and ligand exchange dynamics of the ternary complex (UO2)2(CO3)(OH)3- have been investigatedd by EXAFS and NMR spectroscopy. Very broad signals can be observed in both the 13C and the 17O NMR spectra.
The EXAFS data show the presence of 1.3 ± 0.3 short uranium–oxygen distances at 2.26 Å, consistent with single bonded hydroxide and 3.9 ± 0.6 distances at 2.47 Å for the other ligands in the first co-ordination shell. There is also evidence for a U U interaction at 3.90 Å. 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 other ternary uranium() complexes.