Studies of metal carbonate equilibria. 8. Structure of the hexakis(carbonato)tris[dioxouranate(VI)] ion, (UO2)3(CO3)66-, in aqueous solution. An x-ray diffraction and carbon-13 NMR study

Abstract

The X-ray scattering from moderately concentrated dioxouranium(VI) carbonate solutions with the major part of uranium bound in the trinuclear complex (U02)3(C03)66" has been measured. A model for the structure of this complex consistent with the scattering data and compatible with 13C NMR data is suggested. The complex is triangular with a U-U distance of 4.946 (5) A. There are two sets of coordinated carbonate ions, three bridging and three terminal ones. The latter are bonded through two oxygens to uranium. The bridges are formed through bidentate coordination of the carbonate ion to two uranium atoms. The overall symmetry of the complex is close to Dih, and each uranium(VI) has an approximately hexagonal-bipyramidal coordination geometry, similar to those found in e.g. U02C03(s) and K4[U02(C03)3](s). The 13C NMR chemical shifts for the two types of carbonate ions in the complex have been determined to be 168.7 and 167.3 ppm, respectively, from Me4Si.

Coordination Mode and Kinetic Behavior of the Tetracarbonatozirconate Ion

“…Partly for this reason, Raman spectroscopy allows us to distinguish essentially between monodentate and bidentate or bridging coordination modes. 13 C-NMR Spectroscopy provides additional information about the coordination mode.…”

“…The other one with a depolarization factor of 0.9 is depolarized and corresponds to the n C-NMR Spectroscopy. As Raman spectroscopy does not distinguish between a bidentate or bridging coordination mode, 13 C-NMR spectroscopy is used to resolve this last ambiguity. Separately recorded spectra of carbonate and hydrogencarbonate solutions show chemical shifts d at 168.6 and 161, respectively, for the ionic strengths of 1 and 2 mol´l À1 in KNO 3 media.…”

Similarities between the Coordination of Actinide Ions in Solution and the Structures of their Related Crystalline Phases

“…Pair distribution functions (PDF)s, obtained by the Fourier transform of higherenergy x-ray scattering data, are providing new opportunities to probe the coordination environments of actinide ions in solution [14][15][16][17][18][19]. In addition to higher fluxes of tunable x-rays for EXAFS and microprobe studies, the higher critical energies of these sources results in a significant flux of higher energy (> 60 keV) x-rays for use in scattering experiments.…”

Kinetic and thermodynamic study of the Na4(UO2)2(OH)4(C2O4)2 complex

“…EXAFS technique was combined with potentiometric and spectrometry (NMR, RAMAN, and X‐ray diffraction) techniques 6. Since the complexing properties of natural humics isolated from different waters appear to be similar, and the complexation with functional carboxyl groups has been identified as the most suitable mechanism with most radionuclides, the complexation of the UO 2 2+ ion with the oxalate ion 3, 5, 7, 8 have been largely studied.…”