Theoretical Examination of the Thermodynamic Factors in the Selective Extraction of Am³⁺ from Eu³⁺ by Dithiophosphinic Acids

A detailed thermodynamic examination of the selective extraction of Am³⁺ from Eu³⁺ by two dithiophosphinic acids was performed using DFT. By examination of two extractants with two metal ions, the most uncertain terms of these calculations were eliminated, resulting in free energies (ΔΔΔ<i>G</i>_ext) that are directly related to the selectivity data. The calculated relative selectivities agree well with experimental data, indicating that the extraction factor is primarily due to the binding free energy of the ligands to the metals and is not dependent on side reactions or complicated solvent effects

How Does Nishibayashi’s Molybdenum Complex Catalyze Dinitrogen Reduction to Ammonia?

Recently, Nishibayashi et al. reported a dimolybdenum–dinitrogen complex that is catalytic for complete reduction of dinitrogen to ammonia. This catalyst is different from the Schrock molybdenum catalyst in two fundamental aspects: it contains two metal centers, and the oxidation state is Mo⁰ instead of Mo^III. We show that a remarkable feature of the bimetallic complex is the bond-mediated delocalized electronic states, resulting from the two metal centers bridged by a dinitrogen ligand. Using first-principles calculations, we found that this property makes the bimetallic complex the effective catalyst, as opposed to the originally postulated monometallic fragment. A favorable reaction pathway is identified, and the nature of the intermediates is examined. Furthermore, studies of the intermediate states led us to propose possible deactivation processes of the catalyst. The finding that the central bimetallic unit (Mo–N₂–Mo) is relevant for catalytic activity may provide a guideline for the development of more efficient dinitrogen-reducing catalysts

Degradation of Alkali-Based Photocathodes from Exposure to Residual Gases: A First-Principles Study

Photocathodes are a key component in the production of electron beams in systems such as X-ray free-electron lasers and X-ray energy-recovery linacs. Alkali-based materials display high quantum efficiency (QE), however, their QE undergoes degradation faster than metal photocathodes even in the high vacuum conditions where they operate. The high reactivity of alkali-based surfaces points to surface reactions with residual gases as one of the most important factors for the degradation of QE. To advance the understanding on the degradation of the QE, we investigated the surface reactivity of common residual gas molecules (e.g., O₂, CO₂, CO, H₂O, N₂, and H₂) on one of the best-known alkali-based photocathode materials, cesium antimonide (Cs₃Sb), using first-principles calculations based on density functional theory. The reaction sites, adsorption energy, and effect in the local electronic structure upon reaction of these molecules on (001), (110), and (111) surfaces of Cs₃Sb were computed and analyzed. The adsorption energy of these molecules on Cs₃Sb follows the trend of O₂ (−4.5 eV) > CO₂ (−1.9 eV) > H₂O (−1.0 eV) > CO (−0.8 eV) > N₂ (−0.3 eV) ≈ H₂ (−0.2 eV), which agrees with experimental data on the effect of these gases on the degradation of QE. The interaction strength is determined by the charge transfer from the surfaces to the molecules. The adsorption and dissociation of O containing molecules modify the surface chemistry such as the composition, structure, charge distribution, surface dipole, and work function of Cs₃Sb, resulting in the degradation of QE with exposure to O₂, CO₂, H₂O, and CO

Exploring Electrochemical Windows of Room-Temperature Ionic Liquids: A Computational Study

Room-temperature ionic liquids (RTILs) are regarded as green solvents due to their low volatility, low flammability, and thermal stability. RTILs exhibit wide electrochemical windows, making them prime candidates as media for electrochemically driven reactions such as electro-catalysis and electro-plating for separations applications. Therefore, understanding the factors determining edges of the electrochemical window, the electrochemical stability of the RTILs, and the degradation products is crucial to improve the efficiency and applicability of these systems. We present here computational investigations of the electrochemical properties of a variety of RTILs covering a wide range of electrochemical windows. We proposed four different approaches with different degrees of approximation and computational cost from gas-phase calculations to full explicit solvation models. It was found that, whereas the simplest model has significant flaws in accuracy, implicit and explicit solvent models can be used to reliably predict experimental data. The general trend of electrochemical windows of the RTILs studied is well reproduced, showing that it increases in the order of imidazolium < ammonium < pyrrolidinium < phosphonium giving confidence to the methodology presented to use it in screening studies of ionic liquids

Extending Stannyl Anion Chemistry to the Actinides: Synthesis and Characterization of a Uranium–Tin Bond

We have synthesized a rare example of a uranium­(IV) stannyl (κ⁴-N­(CH₂CH₂NSi­(<i>ⁱ</i>Pr)₃)₃­U­(SnMe₃), <b>1</b>) via transmetalation with LiSnMe₃. This complex has been characterized crystallographically and shown to have a U–Sn bond length of 3.3130(3) Å, substantially longer than the only other crystallographically observed U–Sn bond (3.166 Å). Computational studies suggest that the U–Sn bond in <b>1</b> is highly polarized, with significant charge transfer to the stannylate ligand. We briefly discuss plausible mechanistic scenarios for the formation of <b>1</b>, which may be relevant to other transmetalation processes involving heavy main group atoms. Furthermore, we demonstrate the reducing ability of [SnMe₃]⁻ in the absence of strongly donating ligands on U­(IV)

Extending Stannyl Anion Chemistry to the Actinides: Synthesis and Characterization of a Uranium–Tin Bond

We have synthesized a rare example of a uranium­(IV) stannyl (κ⁴-N­(CH₂CH₂NSi­(<i>ⁱ</i>Pr)₃)₃­U­(SnMe₃), <b>1</b>) via transmetalation with LiSnMe₃. This complex has been characterized crystallographically and shown to have a U–Sn bond length of 3.3130(3) Å, substantially longer than the only other crystallographically observed U–Sn bond (3.166 Å). Computational studies suggest that the U–Sn bond in <b>1</b> is highly polarized, with significant charge transfer to the stannylate ligand. We briefly discuss plausible mechanistic scenarios for the formation of <b>1</b>, which may be relevant to other transmetalation processes involving heavy main group atoms. Furthermore, we demonstrate the reducing ability of [SnMe₃]⁻ in the absence of strongly donating ligands on U­(IV)

Extending Stannyl Anion Chemistry to the Actinides: Synthesis and Characterization of a Uranium–Tin Bond

We have synthesized a rare example of a uranium­(IV) stannyl (κ⁴-N­(CH₂CH₂NSi­(<i>ⁱ</i>Pr)₃)₃­U­(SnMe₃), <b>1</b>) via transmetalation with LiSnMe₃. This complex has been characterized crystallographically and shown to have a U–Sn bond length of 3.3130(3) Å, substantially longer than the only other crystallographically observed U–Sn bond (3.166 Å). Computational studies suggest that the U–Sn bond in <b>1</b> is highly polarized, with significant charge transfer to the stannylate ligand. We briefly discuss plausible mechanistic scenarios for the formation of <b>1</b>, which may be relevant to other transmetalation processes involving heavy main group atoms. Furthermore, we demonstrate the reducing ability of [SnMe₃]⁻ in the absence of strongly donating ligands on U­(IV)

Impact of Surface Defects on the Binding Strength of Anticorrosion 2D Nanomaterial Surface Coatings for UO₂

Protection against surface corrosion is essential for ensuring the reliability and long-term durability of uranium materials. Atomically thin two-dimensional (2D) nanomaterials, known for their unique chemical inertness, are particularly promising as anticorrosion coatings. The representative 2D nanomaterials from different classes (insulator, semimetal, semiconductor, and conductor), including BN, graphene, MoSe2, MoS2, and oxygen-passivated Ti2C layers (Ti2CO2 and Ti2CO), were selected to investigate their interactions with the UO2(111) surface using quantum mechanical calculations. Our results show that graphene and h-BN exhibit physical adsorption with the lowest binding energies, less than 1.0 J/m2. In contrast, MoS2 and MoSe2 demonstrate chemical adsorption in the range of 1.0 to 1.5 J/m2. The highest binding energy of 1.7 and 3.1 J/m2 was predicted for Ti2C-based MXenes (Ti2CO2 and Ti2CO, respectively). These results establish the MXene class as the most promising coating for UO2 among the 2D materials considered. It is worth noting that surface defects, whether induced by oxidation or reduction, can influence the strength of the coating, with the primary determinant being the nature of the 2D nanomaterial

A Screened Hybrid DFT Study of Actinide Oxides, Nitrides, and Carbides

A systematic study of the structural, electronic, and magnetic properties of actinide oxides, nitrides, and carbides (AnX_1–2 with X = C, N, O) is performed using the Heyd–Scuseria–Ernzerhof (HSE) hybrid functional. Our computed results show that the screened hybrid HSE functional gives a good description of the electronic and structural properties of actinide dioxides (strongly correlated insulators) when compared with available experimental data. However, there are still some problems reproducing the electronic properties of actinide nitrides and carbides (strongly correlated metals). In addition, in order to compare with the results by HSE, the structures, electronic, and magnetic properties of these actinide compounds are also investigated in the PBE and PBE+U approximation. Interestingly, the density of states of UN obtained with PBE compares well with the experimental photoemission spectra, in contrast to the hybrid approximation. This is presumably related to the need of additional screening in the Hartree–Fock exchange term of the metallic phases

Investigation of the Electronic Structure of Mono(1,1′-Diamidoferrocene) Uranium(IV) Complexes

The electronic structure of several mono­(1,1′-diamido­ferrocene) uranium complexes (NN^R)­UX₂ (NN^R = fc­(NR)₂, fc = 1,1′-ferrocenediyl, R = SiMe₃, Si^<i>t</i>BuMe₂, SiMe₂Ph, X = I, CH₂Ph), (NN^TBS)­UI­(OAr) (OAr = 2,6-di-<i>tert</i>-butylphenoxide), and (NN^TBS)­U­(CH₂Ph)­(OAr) was investigated by electrochemistry, electronic absorption and vibrational spectroscopy, and DFT calculations. Similar metrical parameters were observed for (NN^TBS)­U­(CH₂Ph)₂ and (NN^DMP)­U­(CH₂Ph)₂ (and also for the previously reported (NN^TMS)­UI₂­(THF), (NN^TBS)­UI₂­(THF), and (NN^TBS)­U­(CH₂Ph)­(OAr)) that translate in similar DFT parameters (bond orders, metal charges) despite some small differences observed by electrochemistry and IR or electronic absorption spectroscopy