Use of vibrational spectroscopy to identify the formation of neptunyl–neptunyl interactions: a paired density functional theory and Raman spectroscopy study

Abstract

Actinyl-Actinyl interactions (AAIs) occur in pentavalent actinide systems, particularly for Np(V), and lead to complex vibrational signals that are challenging to analyze and interpret. Previous studies have focused on...

Periodic Density Functional Theory Calculations of Uranyl Tetrachloride Compounds Engaged in Uranyl–Cation and Uranyl–Hydrogen Interactions: Electronic Structure, Vibrational, and Thermodynamic Analyses

“…Additionally, efforts will further be needed to understand related Np and Pu systems to provide added insights into the electronic structure of f -block elements. Only a handful of related Np compounds have been reported in the literature, but these systems display enhanced NCIs compared to their uranyl counterparts. ,,, However, the experimental determination of Δ H f of neptunyl can be far more challenging than that of uranyl systems due to limited availability, high cost, and the increased radioactivity of neptunium-237.…”

“…The binding of these equatorial ligands leads to additional electron donation to the An­(VI) metal center and weakening of the UO yl bond, an effect often observed through red-shifting of the ν 1 and ν 3 modes in Raman and IR spectroscopy. − UO yl bond weakening is known to increase the Lewis basicity of the axial oxo groups, enhancing their ability to interact with Lewis acids through different non-covalent interactions (NCIs) . These second-sphere NCIs, including Coulombic, hydrogen bonding, and halogen bonding, can influence the overall chemical and physical properties of the material, including structural topologies, redox potentials, , and activation of vibrational modes. − …”

Periodic Trends within Actinyl(VI) Nitrates and Their Structures, Vibrational Spectra, and Electronic Properties

“…The actinyl bond is both Raman-active, ν 1 , the symmetric stretching of the dioxo cation, and infrared (IR)-active, ν 2 , the bending mode, and ν 3 , the asymmetric stretching mode. Early studies of uranyl complexes developed empirical relationships between the observed vibrational frequencies, the −yl bond length, and the nature of the equatorial ligand interactions highlighting the correlation between a lengthening uranyl bond and a lower vibrational frequency consistent with Badger’s rules. − Subsequent studies, including our own, have extended these studies to the transuranium molecules with the goal of understanding the periodic properties of the actinyl ions beyond uranium. − …”

Dinuclear Complexes of Uranyl, Neptunyl, and Plutonyl: Structures and Oxidation States Revealed by Experiment and Theory

“…Effective charges in uranyl(VI), for example, are +3.2e on U and −0.6e on O yl , i.e., [ 0.6− O�U 3.2+ �O 0.6− ] 2+ . 3,4 Condensed phase AAIs are prevalent for pentavalent actinyls like neptunyl(V), 5,6 whereas less common for dipositive hexavalent actinyls due to greater Coulombic repulsion. 2,7−9 Small gas-phase complexes are well suited for high-level ab initio electronic structure computations to provide elucidation that may be relevant to understanding more complicated condensed-phase systems.…”

“…The AAI is between polar actinyl cations, [ δ− OAn (2δ+ n )+ O δ− ] n + , where n = 1 for An V and n = 2 for An VI . Effective charges in uranyl­(VI), for example, are +3.2e on U and −0.6e on O yl , i.e., [ 0.6– OU 3.2+ O 0.6– ] 2+ . , Condensed phase AAIs are prevalent for pentavalent actinyls like neptunyl­(V), , whereas less common for dipositive hexavalent actinyls due to greater Coulombic repulsion. ,− …”