Probing the protonation and reduction of heptavalent neptunium with computational guidance.

Influence of pH on the speciation and stability of heptavalent neptunium is poorly understood although it is frequently invoked in the literature to explain experimental observations. The present study employs Density Functional Theory (DFT) methodology to assess the thermodynamic feasibility of protonation reactions for the Np(VII) anion complex and the impact on its reduction to Np(VI). This theoretical framework is then explored experimentally through the titration and systematic protonation of Np(VII) in solution and solid-state samples while monitoring them spectroscopically.

Synthesis, characterization, and density functional theory investigation of (CHN)[NpOCl] and Rb[NpOCl(HO)] chain structures.

The actinyl tetrachloro complex [An(V/VI)OCl] tends to form discrete molecular units in both solution and solid state materials, but related aquachloro complexes have been observed as both discrete coordination compounds and 1-D chain topologies. Subtle differences in the inner sphere coordination significantly influence the formation of structural topologies in the actinyl chloride system, but the exact reasoning for these variations has not been delineated. In the current study, we present the synthesis, structural characterization, and vibrational analysis of two 1-D neptunyl(V) chain compounds: (CHN)[NpOCl] (Np-Gua) and Rb[NpOCl(HO)] (Np-Rb).

Insights into the Mechanism of Neptunium Oxidation to the Heptavalent State.

Neptunium can exist in multiple oxidation states, including the rare and poorly understood heptavalent form. In this work, we monitored the formation of heptavalent neptunium [Np(VII)O(OH)] during ozonolysis of aqueous MOH (M=Li, Na, K) solutions using a combined experimental and theoretical approach. All experimental reactions were closely monitored via absorption and vibrational spectroscopy to follow both the oxidation state and the speciation of neptunium guided by the calculated vibrational frequencies for various neptunium species.

Three-Dimensional Noncovalent Interaction Network within [NpOCl] Coordination Compounds: Influence on Thermochemical and Vibrational Properties.

Noncovalent interactions (NCIs) can influence the stability and chemical properties of pentavalent and hexavalent actinyl (AnO) compounds. In this work, the impact of NCIs (actinyl-hydrogen and actinyl-cation interactions) on the enthalpy of formation (Δ) and vibrational features was evaluated using Np(VI) tetrachloro compounds as the model system. We calculated the Δ values of these solid-state compounds through density functional theory+ thermodynamics (DFT+ T) and validated the results against experimental Δ values obtained through isothermal acid calorimetry.