Matrix-Isolation Infrared Spectra and Electronic Structure Calculations for Dinitrogen Complexes with Uranium Trioxide Molecules UO₃(η¹-NN)_1–4

Abstract

Investigations of the interactions of uranium trioxide (UO 3 ) with other species are expected to provide a new perspective on its reaction and bonding behaviors. Herein, we present a combined matrix-isolation infrared spectroscopy and theoretical study of the geometries, vibrational frequencies, electronic structures, and bonding patterns for a series of dinitrogen (N 2 ) complexes with UO 3 moieties UO 3 (η 1 -NN) 1−4 . The complexes are prepared by reactions of laser-ablated uranium atoms with O 2 /N 2 mixtures or laser-ablated UO 3 molecules with N 2 in solid argon. UO 3 (η 1 -NN) 1−4 are classified as "nonclassical" metal−N 2 complexes with increased Δν(N 2 ) values according to the experimental observations and the computed blue-shifts of N−N stretching frequencies and N−N bond length contractions. Electronic structure analysis suggests that UO 3 (η 1 -NN) 1−4 are σ-only complexes with a total lack of π-back-donation. The energy decomposition analysis combined with natural orbitals for chemical valence calculations reveal that the bonding between the UO 3 moiety and N 2 ligands in UO 3 (η 1 -NN) 1−4 arises from the roughly equal electrostatic attractions and orbital mixings. The inspection of orbital interactions from pairwise contributions indicates that the strongest orbital stabilization comes from the σ-donations of the 4σ*-and 5σ-based ligand molecular orbitals (MOs) into the hybrid 7s/6d x 2 −y 2 MO of the U center. The electron polarization induced by electrostatic effects in the N inner ← N outer direction provides complementary contributions to the orbital stabilization in UO 3 (η 1 -NN) 1−4 . In addition, the reactions of UO 3 with N 2 ligands and the origination of the nonclassical behavior in UO 3 (η 1 -NN) 1−4 are discussed.

Spectroscopic and Theoretical Insights into H2 Activation on Uranium Monoxide: Homolytic H2 Cleavage Mediated by Intermediate OU(η2-H2)

“…The experimental setup and procedures used for investigating the reaction of H 2 with laser-ablated UO molecules have been previously published. , A rotating UO 2 ceramic disc target with a size of Φ 10 mm × 2 mm was ablated by an Nd: YAG laser fundamental beam operating at a laser length of 1064 nm, a repetition rate of 10 Hz, and a pulse width of <10 ns. The typical laser power ranged from 15 to 30 mJ/pulse.…”

CO Oxidation to CO2 on Uranium Dioxide Molecules through Intermediate O2U(η1-CO)

“…The experimental details for investigating CO reactions with laser-ablated UO 2 molecules in solid argon matrices are similar to those in our previous works. 27,29 An Nd:YAG laser fundamental beam (1064 nm wavelength, <10 ns pulse width, and 10 Hz repetition rate) was focused onto a rotating ceramic UO 2 disc target (Φ10 mm*2 mm), which was fabricated by powder sintering for 6.5 h at 1700 K. 30 The typical laser power was 15−20 mJ/pulse. Notice that UO, UO 2 , and UO 3 molecules were produced simultaneously at varying concentrations during laser ablation.…”