Electronic Structures and Unusual Chemical Bonding in Actinyl Peroxide Dimers [An₂O₆]²⁺ and [(An₂O₆)(12-crown-4 ether)₂]²⁺ (An = U, Np, and Pu)

Abstract

As known, actinyl peroxides play important roles in environmental transport of actinides, and they have strategic importance in the application of nuclear industry. Compared to the most studied uranyl peroxides, the studies of transuranic counterparts are still few, and more information about these species is needed. In this work, experimentally inspired actinyl peroxide dimers ([An 2 O 6 ] 2+ , An = U, Np, and Pu) have been studied and analyzed by using density functional theory and multireference wave function methods. This study determines that the three [An 2 O 6 ] 2+ have unique electronic structures and oxidation states, as 2+ . This study demonstrates the significance of two bridging oxo ligands with at most four electron holes availability in ionically directing actinyl and resulting in the unusual multiradical bonding in [(Pu VI/V O 2 ) 2 (O 2 ) 1− ] 2+ . In addition, thermodynamically stable 12-crown-4 ether (12C4) chelated [(An 2 O 6 )(12C4) 2 ] 2+ complexes have been predicted, that could maintain these unique electronic structures of [An 2 O 6 ] 2+ , where the An ← O 12C4 dative bonding shows a trend in binding capacity of 12C4 from κ 4 (U) to κ 3 (Np) and κ 4 (Pu). This study reveals the interesting electronic character and bonding feature of a series of early actinide elements in peroxide complexes, which can provide insights into the intrinsic stability of An-containing species.

Trends in the Electronic Structure and Chemical Bonding of a Series of Porphyrinoid–Uranyl Complexes

“…As it is apparent in Figure , [UO 2 (POR)] and [UO 2 (COR)] − share a similarity in the coordination phenomenon that the uranyl resides above the L 4 ligand in [UO 2 (L 4 )] 0/1– and lies between two ligands in [UO 2 (L 4 ) 2 ] 2–/4– . These structures have been commonly reasonable because the small cavities of these two ligands are not enough to accommodate uranyl ions, which have been found in actinyl crown ether complexes. − The side-on complexes are undercoordinated, which further tend to coordinate with other molecules to satisfy the equatorial coordination. For example, the [UO 2 (ORA)­(H 2 O) 2 ] − with two-water coordination shows a larger B.E, compared to that of side-on [UO 2 (ORA)] − (Table S1).…”

Theoretical Insights into the Substitution Effect of Phenanthroline Derivatives on Am(III)/Eu(III) Separation

“…Based on the best-substituted site, as discussed below, we explored the effect of electron-withdrawing (Br, CF 3 ) and electron-donating (OH) groups on Am­(III)/Eu­(III) separation (displayed in Scheme ). Computational chemistry can provide reliable results for the more complicated calculations in actinide chemistry, thanks to its exciting development. − We theoretically explored different substituent groups of Et-Tol-DAPhen and evaluated the Am­(III)/Eu­(III) separation performance. This work can provide useful information in understanding the role of electron-withdrawing and electron-donating groups in tuning the selectivity of Et-Tol-DAPhen derivatives and pave the way for designing new ligands modified by substituted groups with better An­(III)/Ln­(III) selectivity.…”

Multiconfiguration Pair-Density Functional Theory for Vertical Excitation Energies in Actinide Molecules

“…MC-PDFT has also been employed to perform geometry optimizations and compute bond dissociation energies of actinide systems . Hu et al used DMRG-PDFT with large active spaces such as (34e, 44o) and (38e, 40o) to understand the electronic structure and bonding features of various oxo-bridged dimeric actinide molecules . However, to describe the correct topology of potential energy surfaces at conical interactions, which are important for spectroscopy and photochemistry, one needs to consider multistate PDFT (MS-PDFT) similar to the MS-CASPT2 and QD-NEVPT2 methods.…”

“…23 Hu et al used DMRG-PDFT with large active spaces such as (34e, 44o) and (38e, 40o) to understand the electronic structure and bonding features of various oxo-bridged dimeric actinide molecules. 24 However, to describe the correct topology of potential energy surfaces at conical interactions, which are important for spectroscopy and photochemistry, one needs to consider multistate PDFT (MS-PDFT) similar to the MS-CASPT2 25 and QD-NEVPT2 26 methods. The recently developed compressed-state multistate PDFT (CMS-PDFT) method 27 has been shown to outperform other multistate PDFT methods 28 in obtaining smooth potential energy surfaces, conical interactions, and accurate dipole moment calculations both for ground and excited states.…”