Observation and investigation of the uranyl tetrafluoride dianion (UO2F42−) and its solvation complexes with water and acetonitrile

Abstract

Bare uranyl tetrafluoride (UO 2 F 4 2À) and its solvation complexes by one and two water or acetonitrile molecules have been observed in the gas phase using electrospray ionization and investigated by photoelectron spectroscopy and ab initio calculations. The isolated UO 2 F 4 2À dianion is found to be electronically stable with an adiabatic electron binding energy of 1.10 AE 0.05 eV and a repulsive Coulomb barrier of $2 eV. Photoelectron spectra of UO 2 F 4 2À display congested features due to detachment from U-O bonding orbitals and F 2p lone pairs. Solvated complexes by H 2 O and CH 3 CN, UO 2 F 4 (H 2 O) n 2À and UO 2 F 4 (CH 3 CN) n 2À (n ¼ 1, 2), are also observed and their photoelectron spectra are similar to those of the bare UO 2 F 4 2À dianion, suggesting that the solvent molecules are coordinated to the outer sphere of UO 2 F 4 2À with relatively weak interactions between the solvent molecules and the dianion core. Both DFT and CCSD(T) calculations are performed on UO 2 F 4 2À and its solvated species to understand the electronic structure of the dianion core and solute-solvent interactions. The strong U-F interactions with partial (d-p)p bonding are shown to weaken the U]O bonds in the [O]U]O] 2+ unit. Each H atom in the water molecules forms a H-bond to a F atom in the equatorial plane of UO 2 F 4 2À , while each CH 3 CN molecule forms three H-bonds to two F ligands and one axial oxygen.

Photoelectron spectroscopy and the electronic structure of the uranyl tetrachloride dianion: UO2Cl42−

“…56,57 These basis sets and pseudopotential are shown to produce reasonably accurate results for excitation energies of actinide complexes. 17,32,49,58 Figure 1 displays the PES spectra of UO 2 Cl 4 2− at four different photon energies. The 157 nm spectrum ( Fig.…”

“…Single-point CCSD(T) energies of the ground and excited states of UO 2 Cl 4 − were calculated at the optimized SR-CCSD(T) geometry of UO 2 Cl 4 2− , generating accurate state-specific SR energies for all the states. The electron detachment energies corresponding to one-electron transitions from the closed-shell ground state of UO 2 Cl 4 2− to the ground and excited states of UO 2 Cl 4 − were obtained using the CASSCF/CCSD(T)/SO approach, 17,[45][46][47][48] which has been shown to generate accurate excitation energies for molecules containing heavy elements. 17,32,49 In this approach, the SO splittings were treated as a perturbation to the SR state energies and were calculated on the basis of CASSCF wavefunctions with the diagonal matrix elements replaced by the individual CCSD(T) state energies.…”

“…SO splitting was calculated by using a state-interacting method with SO pseudopotentials. We also used the CASSCF/CR-EOM-CCSD(T)/SO approach, 17,32,49 where the completely renormalized equation-of-motion CCSD(T) (CR-EOM-CCSD(T), 50 ) energies, derived from the EOM-CCSD calculations with completely renormalized EOM-CCSD(T) corrections as implemented in NWChem 6.0, were used as the diagonal elements. 51 In this approach, the CR-EOM-CCSD(T) calculations were performed on the monoanion at the optimized CCSD(T) geometry of the dianion to obtain the vertical energies of the excited states, with the CCSD(T) energy of the first state used as a reference.…”

“…We have recently studied the isolated UO 2 F 4 2− species by combining photoelectron spectroscopy (PES) and ab initio calculations, revealing that the U-F bonding and the electrostatic repulsion from the F − ligands weaken the axial U-O bonds. 17 The calculated U-O a) E-mail: junli@mail.tsinghua.edu.cn. b) lai-sheng_wang@brown.edu.…”

Gas Phase Reactions of Ions Derived from Anionic Uranyl Formate and Uranyl Acetate Complexes

“…Electrospray ionization (ESI) provides easy access to a wide range of gasphase complexes containing uranium in high oxidation states (+5 and +6) for studies of intrinsic structure and reactivity (i.e., outside of the influence of solvent or other condensed phase effects) in a species specific fashion. For example, the transfer of uranium as mono-positive, pentavalent U V O 2 + from solution to the gas phase using ESI was first reported in 1992 [5] and since then, advances in the fundamental understanding of uranyl coordination chemistry have been made using the ionization method [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Most importantly, ESI has been used to generate gas-phase, doubly charged complexes containing UO 2…”