Bond Lengths Research Articles

Unveiling the Reaction Mechanism of Diels-Alder Cycloadditions between 2,5-Dimethylfuran and Ethylene Derivatives Using Topological Tools.

The [4+2] Diels-Alder cycloaddition reaction between 2,5-DMF (1) and ethylene derivatives (2a-h) activated by electron-withdrawing groups has been studied at the density functional theory levels using a panoply of tools to unravel the reaction mechanisms. From the analysis of the reactivity indices, 2a-h behave as electrophiles while 1 as nucleophile, and the activation of the double bond of ethylene increases its electrophilicity, which is accompanied by an enhancement of the polarity of the reaction. The activation Gibbs free energy decreases linearly as a function of this increase of polarity, as estimated by the electrophilicity difference between the reactants. The difference of electrophilicity drives also the global electron density transfer at the transition state and the asynchronicity of the reaction, as evaluated by the difference of carbon-carbon bond lengths in the transition state. Then, Bonding Evolution Theory shows that the activation of the double bond of ethylene by an electron-withdrawing group changes the reaction mechanism from a one-step synchronous process to a one-step asynchronous process. Generally, the endo pathway is kinetically favored but, thermodynamically, it is the exo pathway. Finally, using the Distortion/Interaction-Activation Strain, it is shown that the endo/exo selectivity is mostly driven by the differences of interaction energies.

HOMAc: A Parameterization of the Harmonic Oscillator Model of Aromaticity (HOMA) That Includes Antiaromaticity.

The harmonic oscillator model of aromaticity (HOMA) offers a straightforward route to quantifying aromaticity that requires no other information than the bond lengths of the conjugated ring in question. Given that such information is often readily obtainable from quantum-chemical calculations, it is pertinent to improve this parametrized model as much as possible. Here, a new version of HOMA is presented where, atypically, the corresponding parameters are derived from the actual bond lengths of both aromatic and antiaromatic (rather than nonaromatic) reference compounds, as calculated with a high-level method. The resulting model, which we denote HOMAc, covers CC, CN, NN, and CO bonds and is tested at eight different levels of theory for 45 (single-ring, multi-ring, carbocyclic, N,O-heterocyclic) molecules across the aromatic-antiaromatic spectrum. Thereby, it is found that HOMAc provides a description of aromaticity and antiaromaticity in better accord with magnetic, energetic, and π-delocalization-based reference data than does the standard parametrization of HOMA. Altogether, the results highlight the possibility to realize more reliable geometry-based probing of (anti)aromaticity with the use of HOMAc and with substantial freedom in the choice of quantum-chemical method.

The chemical bonding and adsorption properties of the umbelliform B6Fe cluster

The interesting report [J. Am. Chem. Soc. 2016, 138, 5644−5651] is that the FeB6 monolayers have pronounced stabilities, in which planar hypercoordinate Fe atoms are located at the centre of six-membered boron rings. Here, we find that the potential energy surface of the FeB6 cluster has a single deep funnel that leads down to an umbelliform structure of the global minimum with the triplet state, which is 0.17 eV lower than that of the reported C2v plane. The chemical bonding analysis by the AdNDP reveals that the FeB6 has six localised two-centre two-electron (2c–2e) B–B bonds and six localised 2c–2e B–Fe bonds|, and the remaining two 7c–1e σ bonds are delocalised over the umbelliform structure, which is further confirmed by the ELF, LOL and bond order analyses. After the CO molecule is adsorbed on the FeB6, it prefers to be located at the top site of Fe atom. The adsorption energy is 1.34 eV that is due to the σ-donation from the CO 5σ orbital to the Fe. The charge transfer makes the C–O stretching frequency and bond length have a red-shift.

Jimkrieghite, Ca(C2H3O3)2, a New Glycolate Mineral, from the Santa Catalina Mountains, Tucson, Arizona, USA

ABSTRACT A new organic mineral species, jimkrieghite, ideally Ca(C2H3O3)2, was discovered from the western end of Pusch Ridge in the Santa Catalina Mountains, north of Tucson, Arizona, USA. It occurs as pseudo-cubic or thick-tabular crystals (up to 0.12 × 0.12 × 0.10 mm) associated with calcite, cerussite, chrysocolla, hematite, lazaraskeite, malachite, microcline, mimetite, phlogopite, phosphohedyphane, quartz, stanevansite, and wulfenite. Jimkrieghite is colorless and transparent with a white streak and vitreous luster. It is brittle and has a Mohs hardness of ∼2½; cleavage is perfect on {100}. No twinning was observed. The measured and calculated densities are 1.85(5) and 1.879 g/cm3, respectively. Optically, jimkrieghite is biaxial (−), with α =1.539(5), β = 1.579(5), γ = 1.595(5), 2Vmeas. = 68(3)°, 2Vcal. = 63°. Calcium is the only metal cation detected by electron microprobe, and the chemical formula was derived from the structural data showing that jimkrieghite is an anhydrous calcium glycolate. Jimkrieghite is orthorhombic with space group Pbca and unit-cell parameters a = 9.01716(12), b = 9.70761(11), c = 15.3554(2) Å, V = 1344.13(3) Å3, and Z = 8. It is isostructural with the orthorhombic Pbca form of synthetic Cd(C2H3O3)2. In the structure of jimkrieghite, edge-sharing dimers of [CaO8] polyhedra link with one another by corner sharing to form a polyhedral layer parallel to (001). Two different (C2H3O3)− glycolate anions form linkages between the [CaO8] polyhedra. One links polyhedra only within the same layer, whereas the other links polyhedra in adjacent layers, thereby creating a three-dimensional framework. The eight O atoms coordinated to a Ca atom are from five (C2H3O3)− groups, three being bidentately bonded and two monodentately bonded, with the Ca–O bond lengths ranging from 2.369 to 2.868 Å. The discovery of jimkrieghite, together with other glycolate minerals documented thus far, namely lazaraskeite Cu(C2H3O3)2, stanevansite Mg(C2H3O3)2·2H2O, lianbinite (NH4)(C2H3O3)(C2H4O3), and glecklerite Na(C2H3O3), implies that glycolate minerals may be rather widespread in nature, thus serving as a potential reservoir for biologically fixed carbon.

Adsorption of lithium, sodium, gallium, and sulfur atoms onto a GaS monolayer

Abstract Hexagonal gallium sulfide (GaS) monolayer is a very promising monochalcogenide for applications such as electronics, optoelectronics, and catalysts. The adsorption and the diffusion of lithium (Li), sodium (Na), gallium (Ga), and sulfur (S) atoms onto the 2 × 2-GaS hexagonal monolayer are investigated using density functional theory (DFT), along with atomic pseudopotentials. The values of the calculations for the adsorption energy show that the energetically most favorable site for the Li, Na, and Ga adsorbates is the H site, while the most energetically favorable site for the S adsorbate is the TS site. The values calculated for the adsorption energy at the energetically most favorable sites for the Li, Na, Ga, and S atomic adsorbates are −1.853 eV, −1.378 eV, −1.028 eV, and −1.525 eV, respectively. Analysis of the structural properties revealed that after the adsorption process, the GaS+ads system maintains its structure and geometry, since the lattice constants and the lGa-Ga, lGa-S, and lS-S bond lengths do not change significantly with respect to the pristine monolayer. The diffusion of Li, Na, Ga, and S atoms on the 2 × 2-GaS monolayer’s surface shows energy barriers of 28 meV, 40 meV, 72 meV, and 161 meV, respectively. From the total density of states (DOS), it is established that in all cases the GaS+ads monolayer system acquires metallic behavior. Finally, analysis of the Bader charge of the GaS+ads system just at the energetically most favorable sites shows that the Li and Na atoms transfer charge to the monolayer (cations), becoming ionized, while the Ga and S atoms transfer and gain charge from the monolayer, respectively, becoming partially ionized. This electronic behavior makes the GaS monolayer a promising material for use as an anode in batteries.

A computational study on the effect of structural isomerism on the excited state lifetime and redox energetics of archetype iridium photoredox catalyst platforms [Ir(ppy)2(bpy)]+ and Ir(ppy)3.

This study investigates the impact of structural isomerism on the excited state lifetime and redox energetics of heteroleptic [Ir(ppy)2(bpy)]+ and homoleptic Ir(ppy)3 photoredox catalysts using ground-state and time-dependent density functional theory methods. While the ground- and excited-state reduction potentials differ only slightly among the isomers of these complexes, our findings reveal significant variations in the radiative and non-radiative decay rates of the reactivity-controlling triplet 3MLCT states of these closely related species. The observed differences in radiative decay rates could be traced back to variations in the transition dipole moment, vertical energy gaps, and spin-orbit coupling of the isomers. In [Ir(ppy)2(bpy)]+, transition dipole moment differences play a significant role in controlling the relative lifetime of the triplet states, which we rationalized by a vectorial analysis of permanent dipole moments of the ground and excited states. Regarding the two isomers of Ir(ppy)3, changes in radiative decay rates were primarily attributed to variations in vertical energy gaps and intensity borrowing from other singlet-singlet transitions driven by spin-orbit coupling. Non-radiative decay variations were assessed in terms of differences in reorganization energies, adiabatic energy gap, and spin-orbit coupling. For both complexes, reorganization energies associated with low-energy molecular vibrations and metal-ligand bond length changes following the de-excitation process were major contributors. These insights provide a deeper understanding of how molecular design can be leveraged to optimize the performance of iridium-based photoredox catalysts, potentially guiding the development of more efficient catalytic systems for future applications.

Theoretically Guided Development of Excitation-Wavelength-Dependent Multifunctional Phosphor Based on Gallium Vacancy Perturbation.

Constructing multifunctional phosphors grounded in the intricate relationship between energy level structures and luminescent properties has captivated researchers in the luminescent material field. Herein, using the embedded cluster multiconfigurational ab initio method, the energy levels of Bi3+ in the SrLaGa3O7 host at different geometries were calculated, which results in the establishment of complete configurational coordinate curves, yielding breathing mode vibrational frequencies and equilibrium bond lengths for all excited states. These curves supply deep insight into the luminescence properties of Bi3+-doped phosphors and highlight the impact of ions in the second coordination sphere on luminescence. Inspired by the calculated results, we designed SrLaGa3(1-x)O7-δ:0.01 Bi3+ phosphors with different Ga3+ reductions. The artificially introduced gallium vacancy results in perturbed Bi3+ luminescence, as verified by systematic experimental analysis, and causes the material to exhibit a novel greenish-yellow emission band in addition to the original blue band, leading to excitation-wavelength-dependent multicolor emission phosphors. The obtained phosphor displayed a multicolor fluorescent anticounterfeiting function, and a multicolor switching system was designed with the merits of direct visualization and easy identification of encrypted information. Additionally, white light-emitting diodes were fabricated by employing the prepared phosphors and UV chips. These results indicate that the SrLaGa3(1-x)O7-δ:0.01 Bi3+ phosphor has significant potential in both anticounterfeiting and lighting applications. Our study demonstrates the necessity of considering two coordinate spheres of ligands when interpreting the luminescent properties and illustrates the effectiveness of spectral design under theoretical guidance, providing a feasible path for the development of multifunctional phosphors.

(2,9-Dimethyl-1,10-phenanthroline)bis[2-(pyridin-2-yl)phenyl]iridium(III) hexafluorophosphate and (2,9-dimethyl-1,10-phenanthroline)bis[5-methyl-2-(pyridin-2-yl)phenyl]iridium(III) hexafluorophosphate–diethyl ether–acetonitrile (1/0.61/0.78)

The title compounds, [Ir(C14H12N2)(C11H8N)2]PF6 (1) and [Ir(C14H12N2)(C12H10N)2]PF6·0.61C2H10O·0.78CH3CN (2), crystallize in the space groups Pbca and P 1, respectively, each structure containing one monocationic Ir complex and one PF6 − anion in the asymmetric unit. The anion and solvent in compound 2 are disordered. The Ir—N(phenanthroline) bond lengths of ca. 2.21 Å indicate a greater steric effect of the 2,9-dimethyl-1,10-phenanthroline ligand compared to 1,10-phenanthroline. Both structures show offset parallel intermolecular π–π interactions between the pyridine rings of the phenanthroline ligands, and that of 1 also exhibits similar interactions between the phenyl and pyridine rings of the phenylpyridine ligands.

Experimental Investigation of Cadmium Isotope Fractionation during Adsorption on Montmorillonite and Kaolinite.

Cadmium (Cd) isotopes have recently emerged as novel tracers of Cd sources and geochemical processes. Widespread clay minerals play a key role in Cd migration due to their strong adsorption capacity, but the mechanism of Cd isotope fractionation during adsorption onto clay minerals is poorly understood. Here, we experimentally investigated the adsorption mechanisms of Cd on montmorillonite (2:1) and kaolinite (1:1) by using extended X-ray absorption fine structure (EXAFS) spectroscopy. Our results show that lighter Cd isotopes are preferentially adsorbed on clay minerals, with Δ114/110Cddissolved-adsorbed values of 0.03 ± 0.02‰ for montmorillonite and 0.03 ± 0.03‰ for kaolinite. These values are independent of the pH, initial Cd concentration, and ionic strength. EXAFS indicate that the adsorbed Cd forms octahedral outer-sphere surface complexes with an average Cd-O bond length of 2.25-2.26 Å, identical to Cd-O bonding environment in the Cd(NO3)2 solution. Our results demonstrate that the extent of Cd isotope fractionation is constrained by structural changes (including the bond length and coordination number) in surface complexes. These findings suggest that Cd adsorption on clay minerals has a minimal impact on the variability of Cd isotopic compositions in soils and sediments, implying that variations in Cd isotope ratios in soils and sediments primarily reflect changes in Cd sources.

Carbonless DNA.

Carbonless DNA was designed by replacing all carbon atoms in the standard DNA building blocks with boron and nitrogen, ensuring isoelectronicity. Electronic structure quantum chemistry methods (DFT(ωB97XD)/aug-cc-pVDZ) were employed to study both the individual building blocks and the larger carbon-free DNA fragments. The reliability of the results was validated by comparing selected structures and binding energies using more accurate methods such as MP2, CCSD, and SAPT2+3(CCD)δMP2. Carbonless analogs of DNA components, including cytosine, thymine, guanine, adenine, and deoxyribose, were investigated, showing strong resemblance to the carbon-based versions in terms of spatial structure, polarity, and molecular interaction capabilities. Complementary base pairs of the carbonless analogs exhibited a similar number and length of hydrogen bonds as those found in their carbon-containing counterparts, with binding energies for A-T and G-C analogs remaining comparable. Carbonless DNA fragments containing two and six base pairs were studied, revealing double-helix structures analogous to natural DNA. Structural parameters such as fragment size, hydrogen bond lengths, and rise per base pair were consistent with those observed in unmodified DNA. Docking simulations with a 12 base pair fragment and netropsin as a ligand indicated a slight shift in binding preference for the carbonless DNA through the minor groove, with an approximate 25% increase in binding affinity compared to natural DNA.

Molecular Design and Theoretical Study on Dioxadiazine Energetic Compounds Involving Intramolecular Hydrogen Bonds

ABSTRACTThe high nitrogen and high oxygen content of energetic dioxadiazine compounds makes them exhibit high detonation performance and good stability, showing possible application in both military and civilian fields. Energetic dioxadiazine compounds with intramolecular hydrogen bonds were designed and optimized, while introducing —NH2, —NHNO2, —CH3, —NO2, and —OH as modified groups. The bond order, density, enthalpy of formation, stability, detonation performance and inter/intramolecular interactions were analyzed. Results showed that the skeleton of 1,4,2,6‐dioxadiazine and 1,4,2,5‐dioxadiazine had good stability and symmetrical structure. Analysis of bond length revealed the strong hydrogen bonding between the hydroxyl group and dioxadiazine ring. The introduction of —NH2 and —OH groups proved beneficial in increasing molecular planarity. Bond order analysis, molecular electrostatic potential (ESP) analysis and detonation parameter calculations showed that B5 and C5 have good stability and detonation properties. Crystal structure prediction suggested that B5 would most likely crystallize in monoclinic (P21 space group) while C5 would crystallize in orthorhombic (Pbca space group). Hirshfeld surface analysis indicated strong O···H and N···H interactions for compounds B5 and C5. The above results have a positive promoting effect on obtaining high‐energy dioxadiazine compounds with high stability.

Force-Activated Spin-Crossover in Fe2+ and Co2+ Transition Metal Mechanophores.

Transition metal mechanophores exhibiting force-activated spin-crossover are attractive design targets, yet large-scale discovery of them has not been pursued due in large part to the time-consuming nature of trial-and-error experiments. Instead, we leverage density functional theory (DFT) and external force explicitly included (EFEI) modeling to study a set of 395 feasible Fe2+ and Co2+ mechanophore candidates with tridentate ligands that we curate from the Cambridge Structural Database. Among nitrogen-coordinating low-spin complexes, we observe the prevalence of spin crossover at moderate force, and we identify 155 Fe2+ and Co2+ spin-crossover mechanophores and derive their threshold force for low-spin to high-spin transition (FSCO). The calculations reveal strong correlations of FSCO with spin-splitting energies and coordination bond lengths, facilitating rapid prediction of FSCO using force-free DFT calculations. Then, among all Fe2+ and Co2+ spin-crossover mechanophores, we further identity 11 mechanophores that combine labile spin-crossover and good mechanical robustness that are thus predicted to be the most versatile for force-probing applications. We discover two classes of mer-symmetric complexes comprising specific heteroaromatic rings within extended π-conjugation that give rise to Fe2+ mechanophores with these characteristics. We expect the set of spin-crossover mechanophores, the design principles, and the computational approach to be useful in guiding the high-throughput discovery of transition metal mechanophores with diverse functionalities and broad applications, including mechanically activated catalysis.

Prediction of Thermodynamic Properties of C60-Based Fullerenols Using Machine Learning.

Traditional machine learning methods face significant challenges in predicting the properties of highly symmetric molecules. In this study, we developed a machine learning model based on graph neural networks (GNNs) to accurately and swiftly predict the thermodynamic and photochemical properties of fullerenols, such as C60(OH)n (n = 1 to 30). First, we established a global method for generating fullerenol isomers through isomer fingerprinting, which can generate all possible isomers or produce diverse structural types on demand. Significantly, by incorporating interpretable descriptors such as atomic labels, bond lengths, and bond angles from highly symmetric isomers, our multilayer GNN model achieved over 90% accuracy in predicting the thermodynamic stability of fullerenols. The model also performed excellently in predicting electronic properties, including the highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), and the energy gap. Overall, this work demonstrates a new strategy using interpretable descriptors for accurately predicting the properties of highly symmetric structures, offering theoretical chemists a valuable tool for studying these materials.

Crystal structures of three salts of the triphenylsulfonium ion

The reactions of triphenylsulfonium chloride ([TPS][Cl]) with various acids in methanol yield the corresponding salts triphenylsulfonium triiodide, C18H15S+·I3 − or [TPS][I3] (I), triphenylsulfonium perchlorate, C18H15S+·ClO4 − or [TPS][ClO4] (II), and triphenylsulfonium hexafluorophosphate, C18H15S+·PF6 − or [TPS][PF6] (III), as crystalline products. These crystals were structurally characterized by single-crystal X-ray diffraction. In all three compounds, the sulfur atom in the triphenylsulfonium cation adopts a distorted trigonal–pyramidal geometry. [TPS][I3] (I) and [TPS][PF6] (III) both crystallize in the space group P21/n, while [TPS][ClO4] (II) crystallizes in P21. The S—C bond lengths are comparable across the three salts, and the S—C—S bond angles are consistently between 102 and 106°. Hirshfeld surface analyses reveal that each structure is dominated by hydrogen-based intermolecular contacts, supplemented by anion-specific interactions such as I...H in (I), O...H in (II), and F...H in (III). These contacts organize the ions into mono-periodic ribbon- or chain-like arrangements. No significant π–π stacking is observed.

Confining Phosphoric Acid in Quaternized COF Channels for Ultra-stable and Fast Anhydrous Proton Transport.

Phosphoric acid (H3PO4) doping is a widely employed strategy to facilitate anhydrous proton transport in high-temperature proton exchange membrane fuel cells (HT-PEMFCs). However, significant H3PO4 leaching during long-term operation poses critical challenges to maintaining membrane stability and proton conductivity. Herein, H3PO4 is incorporated into positively charged nanochannels of quaternized covalent organic framework membranes (QACOFMs), leveraging strong electrostatic interactions and confinement effects to achieve exceptional H3PO4 retention under hydration conditions. Moreover, the shortened hydrogen bond length between H3PO4 (O-H…O <2.7 Å) and the highly interconnected hydrogen bond network in the H3PO4@QACOFMs facilitate ultra-fast anhydrous proton transport. As a result, the H3PO4@QACOFMs exhibit superior anhydrous proton transport in a broader temperature range (60-200 oC) and the highest proton conductivity reaches about 379.7 mS cm-1 at 200 oC.

Theoretical study on highly nitrated sensitive pyrazole isomers in the presence of external electric field.

This article mainly studies three isomers of C5H3N7O10, namely 5-methyl-3,4-dinitro-1- (trinitromethyl) -1H pyrazole (1), 4-methyl-3,5-dinitro-1- (trinitromethyl) -1H pyrazole (2), and 3,5-bis (dinitromethyl) -4-nitro-1H-pyrazole (3). These three substances are excellent candidates for energetic materials, but their properties under external electric fields (EEF) have not been studied. Therefore, this article studied the properties of three isomers under EEF using density functional theory (DFT), and conducted statistical analysis on the obtained data, including the molecular structure, frontier molecular orbitals, surface electrostatic potential, and nitrate charge of the three isomers. The results showed that applying EEF to the trigger bonds of 1 and 2 increased bond length, leading to a decrease in material stability. The change in bond length induced by 3 was relatively stable, and the results obtained from calculating the nitro charge were consistent with the bond length results. When an EEF is applied to three substances, the polarization degree of the molecules of the three substances increases. It is worth mentioning that the polarization degree of the molecules under the influence of a negative EEF is greater than that of a positive EEF. Using density functional theory, the B3LYP/6-311 + G (d, p) method was employed for structural optimization. After optimizing convergence, ensure that there are no imaginary frequencies to obtain a stable structure. Wave function analysis was performed using Multiwfn 3.8 and VMD 1.9.3. The EEF strength ranged from - 0.02 a.u. to 0.02 a.u., with a growth gradient of 0.005 a.u.

Analysis of Microstructure Molecular Dynamics and Slag–Metal Reaction of Low‐Basicity CaOSiO2Al2O3MgO System Refining Slag

To clarify the effect of slag composition changes on the slag–metal interface reaction, the microstructure of the CaOSiO2Al2O3MgO system molten refining slag is analyzed using molecular dynamics simulation. In the simulation results, it is shown that in the slag, the SiO bond and AlO bond mainly exist in a tetrahedral coordination, mainly including five structural forms: Q0, Q1, Q2, Q3, and Q4. In addition, AlO also exists in a pentahedral and hexahedral coordination. With the increase of basicity, the proportion of aluminum–oxygen tetrahedral structure in the slag increases, the AlO bond length decreases, and the average diffusion ability of each atom in the slag increases, which can promote the reduction of aluminum in the slag into the steel melt. With the increase of Al2O3 content, the degree of slag polymerization increases, the proportion of pentacoordinated and hexacoordinated aluminum increases, the AlO bond length increases, and the average diffusion ability of each atom in the slag decreases, which can inhibit the reduction of aluminum in the slag into the steel melt.

Achieving Photocatalytic Overall Nitrogen Fixation via an Enzymatic Pathway on a Distorted CoP4 Configuration

AbstractPhotocatalytic nitrogen (N2) fixation over semiconductors has always suffered from poor conversion efficiency owing to weak N2 adsorption and the difficulty of N≡N triple bond dissociation. Herein, a Co single‐atom catalyst (SAC) model with a C‐defect‐evoked CoP4 distorted configuration was fabricated using a selective phosphidation strategy, wherein P‐doping and C defects co‐regulate the local electronic structure of Co sites. Comprehensive experiments and theoretical calculations revealed that the distorted CoP4 configuration caused a strong charge redistribution between the Co atoms and adjacent C atoms, minimizing their electronegativity difference. Consequently, the N2 adsorption pattern switched from an “end‐on” to a “side‐on” mode with a high N2 adsorption energy of −1.40 eV and an elongated N−N bond length of 1.20 Å, notably decreasing the N2 adsorption/activation energy barrier. In the absence of sacrificial agents, the Co SAC achieved excellent photocatalytic overall N2 fixation performance via an enzymatic pathway. The NH3 yielding rate peaked at 1249.5 μmol h−1 g−1 with an apparent quantum yield of 3.51 % at 365 nm. Moreover, the selective phosphidation strategy has universality for synthesizing other SACs, such as those containing Ni and Fe. This study offers new insight into co‐regulating the electronic structure of SACs for efficient photocatalytic overall N2 fixation.

A Closer Look at the FeS Heme Bonds in Azotobacter vinelandii Bacterioferritin: QM/MM and Local Mode Analysis

ABSTRACTUsing the QM/MM methodology and a local mode analysis, we investigated a character and a strength of FeS bonds of heme groups in oxidized and reduced forms of Bacterioferritin from Azotobacter vinelandii. The strength of the FeS bonds was correlated with a bond length, an energy density at a bond critical point, and a charge difference of the F and S atoms. Changing the oxidation state from ferrous to ferric generally makes the FeS bonds weaker, longer, more covalent, and more polar. We also investigated the SFeS bond bending and found that the stronger FeS bond, generally makes the SFeS bond bending stiffer, which could play a key role in the balance between ferric and ferrous oxidation states and related biological activities.

Structural and electronic features enabling delocalized charge-carriers in CuSbSe2

Inorganic semiconductors based on heavy pnictogen cations (Sb3+ and Bi3+) have gained significant attention as potential nontoxic and stable alternatives to lead-halide perovskites for solar cell applications. A limitation of these novel materials, which is being increasingly commonly found, is carrier localization, which substantially reduces mobilities and diffusion lengths. Herein, CuSbSe2 is investigated and discovered to have delocalized free carriers, as shown through optical pump terahertz probe spectroscopy and temperature-dependent mobility measurements. Using a combination of theory and experiment, the critical enabling factors are found to be: 1) having a layered structure, which allows distortions to the unit cell during the propagation of an acoustic wave to be relaxed in the interlayer gaps, with minimal changes in bond length, thus limiting deformation potentials; 2) favourable quasi-bonding interactions across the interlayer gap giving rise to higher electronic dimensionality; 3) Born effective charges not being anomalously high, which, combined with the small bandgap (≤1.2 eV), result in a low ionic contribution to the dielectric constant compared to the electronic contribution, thus reducing the strength of Fröhlich coupling. These insights can drive forward the rational discovery of perovskite-inspired materials that can avoid carrier localization.