Gas-Phase Reactions of the Bare Th²⁺ and U²⁺ Ions with Small Alkanes, CH₄, C₂H₆, and C₃H₈: Experimental and Theoretical Study of Elementary Organoactinide Chemistry

Abstract

The gas-phase reactions of two dipositive actinide ions, Th(2+) and U(2+), with CH(4), C(2)H(6), and C(3)H(8) were studied by both experiment and theory. Fourier transform ion cyclotron resonance mass spectrometry was employed to study the bimolecular ion-molecule reactions; the potential energy profiles (PEPs) for the reactions, both observed and nonobserved, were computed by density functional theory (DFT). The experiments revealed that Th(2+) reacts with all three alkanes, including CH(4) to produce ThCH(2)(2+), whereas U(2+) reacts with C(2)H(6) and C(3)H(8), with different product distributions than for Th(2+). The comparative reactivities of Th(2+) and U(2+) toward CH(4) are well explained by the computed PEPs. The PEPs for the reactions with C(2)H(6) effectively rationalize the observed reaction products, ThC(2)H(2)(2+) and UC(2)H(4)(2+). For C(3)H(8) several reaction products were experimentally observed; these and additional potential reaction pathways were computed. The DFT results for the reactions with C(3)H(8) are consistent with the observed reactions and the different products observed for Th(2+) and U(2+); however, several exothermic products which emerge from energetically favorable PEPs were not experimentally observed. The comparison between experiment and theory reveals that DFT can effectively exclude unfavorable reaction pathways, due to energetic barriers and/or endothermic products, and can predict energetic differences in similar reaction pathways for different ions. However, and not surprisingly, a simple evaluation of the PEP features is insufficient to reliably exclude energetically favorable pathways. The computed PEPs, which all proceed by insertion, were used to evaluate the relationship between the energetics of the bare Th(2+) and U(2+) ions and the energies for C-H and C-C activation. It was found that the computed energetics for insertion are entirely consistent with the empirical model which relates insertion efficiency to the energy needed to promote the An(2+) ion from its ground state to a prepared divalent state with two non-5f valence electrons (6d(2)) suitable for bond formation in C-An(2+)-H and C-An(2+)-C activated intermediates.

Rapid Determination of Uranium in Water Samples by Adsorptive Cathodic Stripping Voltammetry Using a Tin-Bismuth Alloy Electrode

“…The tight convergence criteria and no symmetry restrictions were used during the optimizations. Previous studies have been shown that the main features of actinide complexes can be accurately reproduced at this level of theory [43][44][45].…”

Theoretical investigations of spin‐orbit coupling and intersystem crossing in reaction carbon dioxide activated by [Re(CO)2]+

“…In this work, intermediate optimization and transition state search were calculated by B3LYP (the Becke's three‐parameter hybrid functional (B3) combined with the Lee‐Yang‐Parr (LYP) correlation functional) method of density functional theory (DFT). It is the most widely used functional and corresponds with experimental value . In addition, for obtaining more reliable structural parameters, M06‐L method also was used.…”

Chemie mit Methan: Studieren geht über Probieren!

“…5f-Orbitalen experimentell und theoretisch untersucht worden. [123] Interessant ist hier der Befund, dass die Insertionseffizienz zur Erzeugung der C-An 2+ -H-oder C-An + -H-Spezies von der Promotionsenergie abhängt, die nçtig ist, um jene elektronisch angeregten Zustände zu erreichen, die zur Bildung zweier kovalenter Bindungen unter Beteiligung von Nicht-5f-Valenzlektronen geeignet sind. [124] Außerdem ist ein Spinwechsel vom Triplett-Grundzustand in den angeregten Singulett-Zustand der Reaktanten erforderlich, um die thermische Dehydrierung von Methan, durch beispielsweise Th 2+ , in einer exothermen Reaktion ablaufen zu lassen.…”