Cation–Cation Interactions in [(UO₂)₂(OH)_n]^4–n Complexes

Abstract

The structures and bonding of gas-phase [(UO2)2(OH)n](4-n) (n = 2-6) complexes have been studied using density functional theory (DFT), MP2, and CCSD(T) methods with particular emphasis on ground state structures featuring cation-cation interactions (CCIs) between the uranyl groups. An interesting trend is observed in the stabilities of members of this series of complexes. The structures of [(UO2)2(OH)2](2+), [(UO2)2(OH)4], and [(UO2)2(OH)6](2-) featuring CCIs are found at higher energies (by 3-27 kcal/mol) in comparison to their conventional μ2-dihydroxo structures. In contrast, the CCI structures of [(UO2)2(OH)3](+) and [(UO2)2(OH)5](-) are respectively degenerate with and lower in energy than the structures with the μ2-dihydroxo format. The origin of this trend lies in the symmetry-based need to balance the coordination numbers and effective atomic charges of each uranium center. The calculated IR vibrational frequencies provide signature probes that can be used in differentiating the low-energy structures and in experimentally confirming the existence of the structures featuring CCIs.

Preorganization of N,O-hybrid phosphine oxide chelators for effective extraction of trivalent Am/Eu ions – a computational study

“…40 For all the atoms, the generalized gradient approximation (GGA)-Becke and Perdew 86 (BP86) 42,43 exchange and correlation functional 44 and the Slater-type basis set triple-z plus (TZP) polarization function is utilized. 45,46 To preserve a balance between the precision and the computational cost, the calculations are completed using a frozen core approximation to the inner shells with [1s 2 ] for C, N, and O, [1s 2 -2p 6 ] for P, [1s 2 -4d 10 ] for Eu and [1s 2 -5d 10 ] for Am, as described in earlier studies. 47,48 In addition, the solvent effect was accounted for using the COSMO continuum solvation model.…”

Uranyl to Uranium(IV) Conversion through Manipulation of Axial and Equatorial Ligands

“…15,16 A key factor in accessing reduction to U V has been shown experimentally and by DFT calculations to be the coordination of the relatively inert -yl oxo groups to electropositive Lewis acids. 11,17,18 This interaction has a strong influence on the UO bonding and results in the U VI/V redox couple shifting to more positive potentials. 19 Exploiting these insights has allowed easier reduction to U IV , a process intrinsic to uranium remediation.…”

Controlling Cation‐Cation Interactions in Uranyl Coordination Dimers by Varying the Length of the Dicarboxylate Linker

“…[71] Stand-alone com-putational studies have assessed stabilities of elementary CCIs in gas-phase uranyl dimers. [72,73] In the present work, electrospray ionization (ESI) of solutions containing uranyl and dicarboxylates was employed to generate gas-phase uranyl coordination complexes for reactivity studies in a quadrupole ion trap mass spectrometer (QIT-MS). Among the species produced were uranyl dimers supported by aliphatic α,ω-dicarboxylates, Cn 2-≡ [OOC-[(CH 2 ) n-2 ]-COO] 2-.…”

“…[ 71 ] Stand‐alone computational studies have assessed stabilities of elementary CCIs in gas‐phase uranyl dimers. [ 72,73 ]…”