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NaLa1–xBixS2 solid solutions with tunable band gaps were synthesized, and their optoelectronic structures and photocatalytic performance were investigated via experimental and theoretical approaches. The solid solution powders with various La/Bi ratios were synthesized with Na2CO3, La2O3, and Bi2O3 as precursors and via sulfurization with flowing CS2 at 800 °C for 2 h. The Vegard’s law behavior of cell parameters showed a perfect Bi/La solid solution in the cubic NaLa1–xBixS2 with the associated linear variation of the lattice constants. On the contrary, the combination of diffuse reflectance ultraviolet–visible spectroscopy with density functional theory (DFT) calculations employing the HSE06 functional reveals a monotonic but nonlinear variation of the band gap of the solid solution. While consistent valence band maximum was obtained in NaLa1–xBixS2—consisting mainly of S 3p orbitals—the conduction band minimum was contributed by discrete Bi orbitals present at more positive potential than La. As a resu...

The interaction between hydrogen sulfide and ZIF-8 was studied via structural characterizations and guest molecule diffusion measurements. It was found that hydrogen sulfide reacts with the ZIF-8 external particle surface to form a surface barrier that excludes the uptake of larger molecules (ethanol) and slows down the uptake of smaller molecules (carbon dioxide). Nonetheless, bulk transport properties were unaltered, as supported by pulsed field gradient nuclear magnetic resonance studies. Dispersion-corrected density functional theory calculations revealed that H2S is consumed by reactions occurring at the ZIF external surface. These reactions result in water and defect formation, both of which were found to be exothermic and independent of both crystallographic facets ({001} and {110}) and surface termination. We concluded that these surface reactions lead to structural and chemical changes to the ZIF-8 external surface that generate surface barriers to molecular transport.

Understanding the degradation mechanisms of zeolitic imidazolate frameworks (ZIFs) is crucial to improve their chemical stability and realize their potential industrial applications. Here, we conduct a comprehensive study utilizing dispersion-corrected density functional theory calculations to investigate the chemical stability of bulk ZIFs and their external surfaces under conditions of acid-gas exposure. We examine the influence of steric factors such as topology and ligand functionalization on the relative chemical stability of prototypical ZIFs (ZIF-2 and ZIF-8), including their hypothetical polymorphs. We find that defect formation is more thermodynamically and kinetically favorable at ZIF external surfaces versus the bulk, and that both topology and ligand functionalization impact defect formation. In addition, we provide a detailed mechanism for the reaction of ZIFs with sulfurous and sulfuric acids, of which the latter serves as a catalyst in potential degradation reactions of ZIFs. We also provid...

We present a study of the effects of oxygen vacancies (Ovac) on the oxygen evolution reaction (OER) on the TiO2-terminated (001) surface of cubic BaTiO3 (cBTO-TiO2) using spin-polarized DFT+U calculations and the standard (cation-based) four proton-coupled-electron-transfer methodology. We find that the excess electrons associated with Ovac’s are involved in charge transfer (CT) to the intermediate adsorbate species HO*, O*, and HOO* and/or new surface oxygen hole states that we identified. The CT is responsible for an increase in these species’ binding energies to the oxygen-deficient surface (cBTO-TiO2–x) to an extent consistent with their electronegativity. The much stronger stabilization of HO* and O* compared to HOO* results in an increased overpotential ηOER on the reduced oxide. This result is at odds with experiment that shows a significantly increased efficiency for oxygen-deficient BTO, suggesting that a different mechanism and/or surface must be involved under the experimental conditions. We al...

Systematic density functional theory calculations that treat the strong on-site 3d electron–electron interactions on iron via a Hubbard Ueff = 3.0 eV and the van der Waals (vdW) interactions between the substrate and adsorbate within the vdW-DF framework are employed to study the adsorption of the iron porphyrin (FeP) molecule to the Pt(111) surface. The more accurate vdW-DF-optPBE and vdW-DF-optB88 functionals found the same binding site to be the most stable and yielded binding energies that were within ∼20% of each other, whereas the binding energies computed with the vdW-DF-revPBE functional were substantially weaker. This work highlights the importance of vdW interactions for organometallic molecules chemisorbed to transition metal surfaces. The stability of the binding sites was found to depend upon the number of Fe–Pt and C–Pt bonds that were formed. Whereas in the gas phase the most stable spin state of FeP is the intermediate spin S = 1 state, the high spin S = 2 state is preferred for the FeP–Pt...

Finding new solar-energy absorber materials is one of the most significant challenges in artificial photosynthesis. Starting from the experimentally available LaTaON2 and LaTiO2N oxynitrides, we use DFT to propose new sunlight absorbing semiconductors. The synthetically unknown YTaON2 and YTiO2N are semiconductors with indirect band gaps of 2.7 eV and 2.9 eV, respectively. For the first time, we compute within Boltzmann transport theory the DOS-averaged effective mass and mobility of LaTaON2, LaTiO2N, YTaON2 and YTiO2N. Our first principles calculations indicate that the Y-based materials possess advantageous dielectric (er ≥ 47), optical (α ≥ 104 cm−1 near band edge), and charge transport properties (me,h*DOS ≈ 0.2; μe,h ≈ 102 cm2 V−1 s−1) for the conversion of solar energy into storable fuels. Herein, our work leads to the complete in silico design of semiconductors for water splitting.

Density functional theory calculations were carried out to study the interaction of various models for methylaluminoxane and the active and dormant species in polymerization with the (110) MgCl2 surface. MAO species may bind to the surface via Al–Cl, Mg–O, and Al−μ-CH3–Mg bonds. Our results suggest that the activity of supported MAO may be higher than of homogeneous MAO because the support stabilizes (AlOMe)n·(AlMe3)m, precursors to the active species in polymerization. Moreover, the support lowers the free energy of formation of species that are active in polymerization relative to those that are dormant. Finally, it may be that the support decreases the energy associated with the cation–anion separation in [Cp2ZrMe]+[Me(AlOMe)n]−, a species that is likely dormant in homogeneous processes, hinting that the support has the possibility of increasing the number of potentially active sites.

In this study we report the synthesis and characterization of [Cu(T1Et4iPrIP)(CH 3 OH)Cl]Cl ( 1 ) (T1Et4iPrIP = tris(1-ethyl-4-isopropyl-imidazolyl)phosphine). T1Et4iPrIP serves as a His 3 biomimetic ligand binding metals through the 3-nitrogen of the imidazolyl group. The structure of 1 features copper(II) bonded to three nitrogen ligands from T1Et4iPrIP along with an oxygen ligand from methanol and a chloride ligand to form slightly distorted square pyramidal geometry with an imidazole group occupying the axial position and the methanol and chloride ligands situated in the basal plane. The weak sigma donation of the ligand set results in low energy d–d electronic transitions and small A ‖ (131 G). Time-dependent DFT calculations (B3LYP, 6-311+G(d,p)) on the optimized structure of 1 in methanol solvent allowed for the assignment of specific electronic transitions in the UV–Vis spectrum. The highest occupied molecular orbital (HOMO) was noted to consist of 65% Cu-d character identified as the d x 2 - y 2 orbital.

Species likely to be present in methylaluminoxane (MAO) are studied via dispersion-corrected DFT, which we show is able to accurately predict thermochemical parameters for the dimerization of trimethylaluminum (TMA). Both cage-like, (AlOMe)n,c, and TMA-bound nanotubes, (AlOMe)n,t·(AlMe3)m, are found to be important components of MAO. The most stable structures have aluminum/oxygen atoms in environments whose average hybridization approaches sp3/sp2. The (AlOMe)n,t·(AlMe3)m isomers with the lowest free energies possess Al−μ-Me–Al bonds. At 298 K a novel Td-(AlOMe)16,c oligomer is one of the most stable structures among the six stoichiometries with the lowest free energies: (AlOMe)20,c·(AlMe3)2, Td-(AlOMe)16,c, (AlOMe)18,c, (AlOMe)20,c·(AlMe3), (AlOMe)10,t·(AlMe3)4, and (AlOMe)20,c. As the temperature rises, the abundance of (AlOMe)n,t·(AlMe3)m decreases, and that of (AlOMe)n,c increases. Because the former are expected to be precursors for the active species in polymerization, this may in part be the reaso...

Some of the most popular computational methods have been utilized to determine a dependency of the acidity trend of the first-row hydrides on a choice of basis set. For about three decades, methyl anion ( CH3−) was known as the strongest base but after Tian et al. were able to produce the gas phase lithium monoxide anion (LiO–) they discovered it was a stronger base than CH3− (Tian et al., Proc Natl Acad Soc USA 2008, 105, 7647). Furthermore, the authors confirmed their experimental results using high-level ab initio methods, namely W1 and W2C composite methods, as well as complete active space-averaged quadratic coupled cluster and Brueckner Doubles with triple excitation contribution (BD(T)) within the aug-cc-pVQZ basis set. These methods are highly demanding in terms of the computational effort as well as a level of expertise needed from the user to correctly conduct such calculations. We have shown that the proper acidity trend, that is, ΔHacid298K(CH4)

Chiral saturated oxygen heterocycles are important components of bioactive compounds. Cyclization of alcohols onto pendant alkenes is a direct route to their synthesis, but few catalytic enantioselective methods enabling cyclization onto unactivated alkenes exist. Herein reported is a highly efficient copper-catalyzed cyclization of γ-unsaturated pentenols which terminates in C-C bond formation, a net alkene carboetherification. Both intra- and intermolecular C-C bond formations are demonstrated, thus yielding functionalized chiral tetrahydrofurans as well as fused-ring and bridged-ring oxabicyclic products. Transition-state calculations support a cis-oxycupration stereochemistry-determining step.

Ethylation of imidazole-4-acetate methyl ester affords 1-ethyl-1H-Imidazol-4-ylacetic acid methyl ester (1) and 1-ethyl-1H-Imidazol-5-ylacetic acid methyl ester (2) in a 3:1 ratio. Both 1 and 2 can be converted to their potassium carboxylate salts, 3 and 4, respectively. Reaction of 3 with CuCl2 in methanol yields [Cu(eia)2]·4MeOH (5·4MeOH) (eia− = 1-ethyl-1H-imidazol-4-yl)acetate). EPR measurement of 5 in methanol glass exhibits near axial symmetry with g⊥ (gx = 2.060, gy = 2.087) and g|| = gz = 2.293 with A||Cu = AzCu = 152 G, A⊥Cu~ 10 G, and AyN = 14 G. Accordingly, the structure of 5·4MeOH reveals Cu(II) in tetragonally distorted octahedral geometry with O, N coordination from eia− and elongated bonding (2.506 A) to methanol oxygens in the axial positions. An infinite 1-dimensional hydrogen bonding network involving methanol molecules is present. DFT studies have been carried out to assist in assignment of electronic transitions. Electrochemical studies on 5 in methanol and DMF reveal quasi-reversible redox behavior for the CuII/I couple while for MeCN a CuI/0 stripping process is seen.

Chiral saturated oxygen heterocycles are important components of bioactive compounds. Cyclization of alcohols onto pendant alkenes is a direct route to their synthesis, but few catalytic enantioselective methods enabling cyclization onto unactivated alkenes exist. Herein reported is a highly efficient copper-catalyzed cyclization of γ-unsaturated pentenols which terminates in CC bond formation, a net alkene carboetherification. Both intra- and intermolecular CC bond formations are demonstrated, thus yielding functionalized chiral tetrahydrofurans as well as fused-ring and bridged-ring oxabicyclic products. Transition-state calculations support a cis-oxycupration stereochemistry-determining step.