Additive-driven microwave crystallization of tyramine polymorphs and salts: a quantum crystallography perspective

Polymorphism - the ability of a compound to exist in multiple crystalline forms - needs to be carefully considered in the design of functional materials, particularly in the context of cocrystallization. Tyramine, a biogenic amine, is a promising candidate for polymorph exploration due to its conformational flexibility and ability to form salts. In this study, we investigate the crystallization of tyramine polymorphs using additives and microwave-assisted techniques. Our findings reveal the formation of a new tyramine polymorph and two distinct salts, highlighting the impact of microwave radiation and additive-driven crystallization on polymorph stability and molecular encapsulation. The study demonstrates that the triclinic tyramine polymorph (T2) is thermodynamically more stable due to its lower electronic energy, whereas the monoclinic form (T1) features slightly stronger intermolecular interactions. Over time, in solution, crystals of barbital-tyramine salts (C1 and C2) begin to form, providing an opportunity to assess structural evolution. Optical properties calculations show significant maximum linear birefringence values (0.164 and 0.255) for two polymorphs of tyramine, whereas for C1, this value decreases to 0.095.

Solid-state calculations for iterative refinement in quantum crystallography using the multipole model

A quantum crystallographic refinement methodology has been developed using theoretical multipole parameters generated directly from solid-state calculations using the CRYSTAL17 program. This refinement method is comparable to other transferable form factor approaches, such as the Invariom model, but in contrast to the Hirshfeld atom refinement, it uses theoretical multipole parameters to describe the electron density from a solid-state calculation performed with CRYSTAL17 in an iterative refinement procedure. For this purpose, a Python3 code named ReCrystal has been developed. To start ReCrystal, a CIF, a Gaussian basis set, a DFT functional and the number of CPUs must be defined. The Pack-Monkhorst and Gilat shrinking factors, which define a lattice in the first Brillouin zone, must also be specified. After k-point sampling, CRYSTAL17 calculates structure factors directly from the static electron density. Multipole parameters are generated from these structure factors using the XD program and are fixed during least-squares refinement. The refinement of the xylitol molecular crystal has shown that the hydrogen atom positions can be determined with reasonable agreement to those obtained in the neutron diffraction experiment. This indicates that the periodic boundary condition in ReCrystal is an improvement over gas phase refinement with HAR. The multipole parameters obtained from ReCrystal can be used for further charge density studies especially if weak interactions are the focus. In this work, we demonstrate the performance of ReCrystal on molecular crystals of the small molecules D/L-serine and xylitol with weak hydrogen-bonding motifs using multipole refinement. The advantage of this approach is that multipole parameters can be obtained from high-resolution calculated diffraction data, no database is required, and errors due to the model and errors resulting from the experiment are clearly separated.

Synergistic experimental and computational investigation of azo-linked porphyrin-based porous organic polymers for CO2 capture

We synthesized a series of azo-linked porphyrin-based porous organic polymers (APPs) with linear, bent, and trigonal linkers (APP-1 to APP-6) and with directly connected tetraphenylporphyrin units (APP-7a, APP-7b and APP-8). The synthesized APPs are amorphous solids demonstrating good thermal stability and diverse BET surface areas. APPs with linkers showed significantly higher surface areas (469 to 608 m2 g-1) compared to those with directly connected tetraphenylporphyrin units (0.3 to 23 m2 g-1). Higher surface areas correlated with enhanced CO2 adsorption, particularly for APP-1, APP-2, and APP-5 with experimental CO2 uptake values of 41 mg g-1, 38 mg g-1, and 38 mg g-1, respectively, at 306 K. The computational study supported the experimental findings and provided insights on how surface area and the local landscape affect the CO2 adsorption. Although the computational models were based on ideal structures, while the experiments revealed the materials were amorphous, the calculated CO2 adsorption capacities were roughly comparable to the experimental results, particularly for the 3D systems (APP-5 and APP-6) and the 2D systems with directly connected building units (APP-7 and APP-8). Porphyrin units in the framework serve as additional binding sites for CO2, especially when unhindered and available on either side of the porphyrin plane. This work highlights the potential of 2D layered APPs and 3D topologies for efficient CO2 capture.

Advancing CO2 Conversion with Cu-LDHs: A Review of Computational and Experimental Studies

Layered Double Hydroxides (LDHs) are versatile materials with tuneable properties. They show promising electro- and photo-catalytic activity in the activation and conversion of CO2. Their unique properties make LDHs pivotal materials in emerging sustainable strategies for mitigating the effect of CO2 emissions. However, the intricate structure-property relationship inherent to LDHs challenges their rational design. In this review, we provide a comprehensive overview of both experimental and computational studies about LDHs for photo- and electro-catalytic conversion of CO2, mainly focusing on Cu-based systems due to their superior performance in producing C2 products. We present a background framework, describing the essentials computational and experimental tools, designed to support both experimentalists and theoreticians in the development of tailored LDH materials for efficient and sustainable CO2 valorisation. Finally, we discuss future potential advancements, emphasizing the importance of new synergistic experimental-computational studies.

Structural Elucidation of Na2/3NiO2, a Dynamically Stabilized Cathode Phase with Nickel Charge and Sodium Vacancy Ordering

NaNiO2 (NNO) has been investigated as a promising sodium-ion battery cathode material, but it is limited by degradation-induced capacity fade. On desodiation, NNO forms multiple phases with large superstructures due in part to Na+-ion vacancy ordering; however, their structures are unknown. Here, we report a structural solution to the Na2/3NiO2 (P'3) desodiated phase using combined Rietveld refinement of high-resolution synchrotron X-ray (SXRD) and neutron powder diffraction (NPD) data, magnetic susceptibility, and 23Na solid-state nuclear magnetic resonance (ssNMR) spectroscopy. Our experimental results are compared to ab initio molecular dynamics (AIMD) simulations, which indicate multiple low-energy structures that are dynamically populated. We observe a combination of competing effects that contribute to the resultant dynamic nature of the structure, including honeycomb ordering of mixed-valence Ni, orbital ordering of Jahn-Teller (JT) distorted Ni3+, and zigzag Na+/vacancy ordering. Our work provides evidence of multiple contributions to the structures of desodiated Na2/3NiO2, along with a framework for investigating the other unsolved desodiated structures. This work may also inform our understanding of the Jahn-Teller evolution in other nickel-rich lithium- and sodium-ion cathodes, such as LiNiO2.

Crystallographic, electronic and vibrational properties of 2D silicate monolayers

Phyllosilicates are promising materials for optoelectronic applications because of their interesting electronic and magnetic properties that can be modulated by specific ionic substitutions. They can be easily exfoliated down to a single layer, enabling their use in specific 2D applications, such as the creation of van der Waals heterostructures and other materials with tailored physical properties. The present work reports a theoretical investigation of the structural, electronic, Raman and infrared properties of the (001) monolayer of phlogopite [K(Mg,Fe)3Si3AlO10(OH)2, with Mg/Fe ratio ≥ 2] and how they change with different Fe2+/Mg2+ substitutions in the structure. Although other cations could occupy the octahedral sheet positions in phlogopite (and phyllosilicate in general), here the focus is only on Fe2+/Mg2+ substitution. To this aim, density functional theory simulations were performed using the B3LYP functional, including long-range interactions in the physical treatment. The structure of the single layer of phlogopite showed a decrease of the tetrahedral rotation angle near the interlayer cations in comparison with that of the bulk mineral, which led to a tetrahedral sheet with a hexagonal pattern close to ideality, and an electronic band structure with a decreased band gap energy, down to about 3 eV. All results were discussed against the few available experimental and theoretical data in the scientific literature, finding good agreement but also further extending the knowledge of this interesting natural 2D material.

Crystal structure and polymorphic forms of auranofin revisited

Auranofin, initially developed as a treatment for rheumatoid arthritis, is currently under extensive investigation as a potential drug for various conditions, including cancer, bacterial infections, and parasitic infections. The compound is a known inhibitor of thioredoxin reductase (TXNRD1) and related selenoproteins. Although preliminary studies on the auranofin crystal polymorphism exist, and a low-quality crystal structure has been reported, a comprehensive crystallographic characterization remains unexplored. Utilizing X-ray crystallography techniques, we conducted detailed structural analysis of auranofin and compared our findings with related organogold compounds. Implementation of Hirshfeld atom refinement (HAR) enabled a more accurate hydrogen atom positioning in the structure. The crystal packing reveals a layered arrangement stabilised by numerous weak hydrogen bonds and dispersive interactions. Notably, our attempts to reproduce the previously reported polymorphic form of auranofin, purportedly more water-soluble, were unsuccessful despite following published protocols. To our knowledge, this is the first study describing a "disappearing polymorph" phenomenon of any pharmaceutically relevant transition metal coordination compound. Our findings may have significant implications for medicinal chemistry and pharmacology of coordination complexes, suggesting the need for systematic revision of historical crystallographic data in this field.

Torsion and Axial Deformations of Chalcogen Helical Chains (S, Se, Te): First Principles Calculations Using Line Symmetry Groups

The atomic structure, electronic, phonon, and optical properties of chalcogen helical chains (S, Se, Te) were studied using line symmetry groups and DFT calculations. The whole possible range of torsion deformations (from 0° to 180°), as well as the range of axial deformations (from 0.6 to 1.6) were considered. For the studied chains, the atomic and electronic structures at the energy minima were found. It was shown that for the considered chalcogen chains, the minimum of electronic energy is in the region of rotation angles ~103-107°. The electronic structure of all chains was considered in the helical Brillouin zone, which made it possible to trace its evolution up to the extreme torsional deformations: 0° (linear chain) and 180° (zigzag chain). A method for obtaining the dispersion of phonon states in the helical Brillouin zone has been developed based on the results of calculations by the CRYSTAL17 program. This allowed us to trace the evolution of phonon dispersion curves under torsion deformations up to their extreme values. Based on the known selection rules for helical polymers, the energies of optical, IR, and Raman transitions were obtained. This allows one to predict the optical properties of atomic chalcogen chains-both in a free state and inside carbon nanotubes.

Electronic structure study of YNbTiO[Formula: see text] and CaNb[Formula: see text]O[Formula: see text] with actinide impurities using compound-tunable embedding potential method

The compound-tunable embedding potential (CTEP) method is applied to study actinide substitutions in the niobate crystals YNbTiO[Formula: see text] and CaNb[Formula: see text]O[Formula: see text]. Two one-center clusters are built and centered on Y and Ca, and 20 substitutions of Y and Ca with U, Np, Pu, Am, and Cm were made in four different oxidation states for each cluster. Geometry relaxation is performed for each resulting structure, and electronic properties are analyzed by evaluating the spin density distribution and chemical shifts of X-ray emission spectra. Though the studied embedded clusters with actinides having the same oxidation state are found in general to yield similar local structure distortions, for Am, Cm and Pu in high "starting" oxidation states the electron transfer from the environment was found, resulting in decrease of their oxidation states. The U substitutions are additionally studied with the use of multi-center models, which can provide both more structural and electronic relaxation and also include charge-compensating vacancies. For "starting" U[Formula: see text] case, the decrease in the oxidation state similar to that of Am[Formula: see text] and Cm[Formula: see text] in one-center clusters is observed in our calculations but in a different way, while for "starting" U[Formula: see text] state the reverse process takes place, resulting in an increase in the oxidation state of uranium to U[Formula: see text]. It is known experimentally that the Nb and Ti atoms in YNbTiO[Formula: see text] are statistically distributed and occupy the same Wyckoff positions. With the CTEP method, it is possible to simulate to a certain extent the effects of such random distribution on the basis of perfect crystal calculation by performing Ti↔Nb substitutions in the embedded clusters. The results were compared to those obtained using the special quasirandom structures (SQS) method with structural relaxation for the single and double cell.

Discovery of a new zinc oxide semiconductor: 21R polytype

Zinc oxide (ZnO) is a notable semiconductor with a range of interesting electronic and optical properties. Polytypic behavior of crystal structures can strongly affect the properties of materials, especially in ZnO. We report the first prediction of a new 21R polytype in zinc oxide with advanced properties. Ab initio calculations were carried out using two-hybrid functionals: HSE06 and PBE0. Structural properties of different ZnO polytypes were investigated, and theoretical data concurred with experimental results. This can be further exploited for various applications based on their unique properties. Electronic properties were studied using band structures and density of states (DOS). Present DFT calculations agree very well with previous calculations and measurements of known ZnO polytypes, and the new 21R polytype is found as a direct band gap semiconductor. The size of the band gap in the case of the hybrid HSE06 functional is calculated to be 2.79 eV and with PBE0 is 3.42 eV. Understanding the structure-property relationship helps in tailoring ZnO for specific applications and optimizing its performance in various technological contexts, especially as an advanced semiconductor material, with possible applications such as 0D, 1D, 2D, and 3D materials.

Water Is Cool: Advanced Phonon Dynamics in Ice Ih and Ice XI via Machine Learning Potentials and Quantum Nuclear Vibrations

Low-dimensional water, despite the relative simplicity of its constituents, exhibits a vast range of phenomena that are of central importance in natural sciences. A large number of bulk as well as nanoscale polymorphs offer engineering possibilities for technological applications such as desalinization, drug delivery, or biological interfacing. However, little is known about the stability of such structures. Therefore, in this study, we employ an array of state-of-the-art computational techniques to study the vibrational properties of ice Ih and XI in their bulk and thin film forms in order to elucidate their structural stability and dynamic behavior. An efficient workflow, consisting of quantum mechanical simulations (based on density functional theory) and machine learning interatomic potentials (MTPs) coupled to temperature-dependent effective potentials (TDEP) and classical molecular dynamics, was verified necessary to capture the temperature-dependent stabilization of the phonons in bulk ice Ih and XI. Anharmonicity and nuclear quantum effects, incorporated in an efficient way through a quantum thermal bath technique, were found crucial to dynamically stabilize low-frequency lattice modes and high-frequency vibrational stretching involving hydrogen. We have identified three novel thin film structures that retain their stability up to at least 250 K and have shed light on their phonon characteristics. In addition, our examination of the Raman spectrum of ice underscores the shortcomings of predicting vibrational properties when relying entirely on the harmonic approximation or purely anharmonic effects. The corrected redistribution of vibrational intensities is found to be achieved only upon inclusion of quantum nuclear vibrations. This was found to be even more crucial for low-dimensional thin film (2D) structures. Overall, our findings demonstrate the significance of joining advanced computational methodologies in unraveling the intricate vibrational dynamics of crystalline ice materials, offering valuable insights into their thermodynamic and structural properties. Furthermore, we suggest a procedure based on MTPs coupled to a quantum thermal bath for the computationally efficient probing of nuclear effects in ice structures, although equally applicable to any other system.

Exploring Forsterite Surface Catalysis in HCN Polymerization: Computational Insights for Astrobiology and Prebiotic Chemistry

Understanding the catalytic role of cosmic mineral surfaces is crucial for elucidating the chemical evolution needed for the emergence of life on Earth and other planetary systems. In this study, the catalytic role of silicate forsterite (Mg2SiO4) surfaces in the synthesis of iminoacetonitrile (IAN, HN=CH-CN) from the condensation of two hydrogen cyanide (HCN) molecules is investigated through quantum mechanical simulations. Using density functional theory calculations, the potential energy surfaces alongside the kinetics of various surface-mediated reactions leading to the formation of IAN are characterized. The effectiveness of forsterite as a catalyst is a delicate balance of the surface reactivity: on one side, the deprotonation of HCN is mandatory to trigger the dimerization; on the other side, the species should be weakly bound to the surface, thus allowing for their diffusion to meet with each other. The work reveals interesting counterintuitive results: the (120) and (101) forsterite surfaces (the less reactive ones) exhibit favorable catalytic properties for the reaction, in detriment to the (111) one (one of the most reactive). The implications of these findings in the astrobiology and prebiotic chemistry fields and for laboratory experiments are discussed, highlighting the potential role of cosmic silicates in the synthesis of complex organic molecules.

Theoretical and Experimental Studies of the Structural Chameleon EuYCuTe3

Layered orthorhombic single crystals of EuYCuTe3 are synthesized using the ampoule method from the elemental precursors taken in the ratio of 1 Eu:1 Y:1 Cu:3 Te by heating up to 1120 K with an excess of CsI as flux. The orthorhombic structure of EuYCuTe3 is established, and structural parameters are obtained using X-ray diffraction. At ambient conditions, the sample crystallizes in the space group Pnma with the unit cell parameters a = 11.2730(7) Å, b = 4.3214(3) Å, c = 14.3271(9) Å. The structure is composed of vertex-connected [CuTe4]7- tetrahedra, which form chains along the [010] direction, and of edge-connected [YTe6]9- octahedra, which form layers parallel to the (010) plane. The Eu2+ cations are found in a capped trigonal prismatic coordination of Te2- anions. The structural phase transition from the α to the β phase is discovered upon heating the sample to 323 K, which comes accompanied with a decrease of [CuTe4]7- tetrahedral distortion. The symmetry of the high-temperature phase is established as ordered in the space group Cmcm (a = 4.3231(3) Å, b = 14.3328(9) Å, c = 11.2843(7) Å). The nature and microscopic mechanism of the phase transition is discussed. By cooling it down below 3 K, the soft ferromagnetic properties of EuYCuTe3 are discovered. The correlation of the ferromagnetic transition temperature in the series of chalcogenides EuYCuCh3 (Ch = S, Se, Te) with the ionic radius of the chalcogenide anion is established. The structural dynamical elastic properties of α- and β-EuYCuTe3 were calculated within the ab initio approach. The vibrational mode frequencies and decomposition on irreducible representations, as well as the degree of ion involvement in each mode, were determined. The calculations reveal an imaginary mode in the Y-point of the Brillouin zone in the high symmetry β-EuYCuTe3 phase. This finding explains the nature of structural reconstruction in EuYCuTe3 crystal as a second-order phase transition induced by soft mode condensation at the edge of the Brillouin zone. The exfoliation of a single layer is simulated theoretically. The exfoliation energy is estimated, and the dynamical properties of EuYCuTe3 single layers are studied.

Photoelasticity of crystals with the scheelite structure: quantum mechanical calculations

We report a complete set of elastic, piezooptic and photoelastic tensor constants of scheelite crystals CaMoO4, BaMoO4, BaWO4 and PbWO4 determined by density functional theory (DFT) calculations using the quantum chemical software package CRYSTAL17. The modulation parameter, i.e. the change in the crystal optical path normalized by thickness and mechanical stress, was calculated based on piezooptic and elastic compliance tensor constants. For the geometries of the most effective piezo-optic interactions, this parameter reaches rather large values (16-17) × 10-12 m2 N-1. Anisotropy of the photoelastic and acoustooptic effects is explored by means of indicative surfaces, considering the directions of light propagation and polarization, the direction of uniaxial compression or lattice distortion caused by the propagation of the acoustic wave. DFT calculations indicate BaWO4 and PbWO4 crystals as the most effective acousto-optic materials, predicting the figure of merit constant M2 ∼ 20 × 10-15 s3 kg-1. The methodology proposed combines the DFT calculations and photoelasticity caused by uniaxial compression of the crystal lattice, with particular emphasis on its anisotropy. It can be considered as part of optical engineering aimed at preliminary assessment of the photoelastic properties of crystal materials, thus assisting in their selection for synthesis and relevant applications.

Electrostatic and Electronic Effects on Doped Nickel Oxide Nanofilms for Water Oxidation

An ideal water-splitting electrocatalyst is inexpensive, abundant, highly active, stable, selective, and durable. The anodic oxygen evolution reaction (OER) is the main bottleneck for H2 production with a complex and not fully resolved mechanism, slow kinetics, and high overpotential. Nickel oxide-based catalysts (NiOx) are highly active and cheaper than precious metal catalysts. However, rigorous catalyst tests and DFT calculations are still needed to rationally optimize NiOx catalysts. In this work, we combine plasma-enhanced atomic layer deposition (PE-ALD) and density functional theory (DFT) to address the role of dopants in promoting NiOx OER activity. Ultrathin films of NiOx doped with Zn2+, Al3+, and Sn4+ presented improved intrinsic activity, stability, and durability for the OER. The results show a low to high catalytic performance of ZnNiOx < NiOx < AlNiOx < SnNiOx, which we attribute to an increase in the concentration of valence band (VB) holes combined with conduction band (CB) electron conductivity, characterized by electrochemical impedance spectroscopy (EIS). The influence of doping on the electronic structure and catalytic activity was investigated using advanced characterization techniques and density functional theory (DFT) calculations (PEB0/pob-TZVP). DFT complements the experimental results, showing that the dopant charge states and orbital hybridization enhance the OER by improving the charge carrier concentration and mobility, thus allowing optimal binding energies and charge dynamics and delocalization. Our findings demonstrate the potential of PE-ALD-doped nanofilms NiOx and DFT to rationally design and develop catalysts for sustainable energy applications.

High Stability, Piezoelectric Response, and Promising Photocatalytic Activity on the New Pentagonal CGeP4 Monolayer

This study introduces the penta-structured semiconductor p-CGeP4 through density functional theory simulations, which possesses an indirect band gap transition of 3.20 eV. Mechanical analysis confirms the mechanical stability of p-CGeP4, satisfying Born-Huang criteria. Notably, p-CGeP4 has significant direct (e 31 = -11.27 and e 36 = -5.34 × 10-10 C/m) and converse (d 31 = -18.52 and d 36 = -13.18 pm/V) piezoelectric coefficients, surpassing other pentagon-based structures. Under tensile strain, the band gap energy increases to 3.31 eV at 4% strain, then decreases smoothly to 1.97 eV at maximum stretching, representing an ∼38% variation. Under compressive strain, the band gap decreases almost linearly to 2.65 eV at -8% strain and then drops sharply to 0.97 eV, an ∼69% variation. Strongly basic conditions result in a promising band alignment for the new p-CGeP4 monolayer. This suggests potential photocatalytic behavior across all tensile strain regimes and significant compression levels (ε = 0% to -8%). This study highlights the potential of p-CGeP4 for groundbreaking applications in nanoelectronic devices and materials engineering.

Open Sn Framework Structure Hosting Bi Guest atoms-Synthesis, Crystal and Electronic Structure of Na13Sn26Bi

The large variety of structures of Zintl phases are generally well understood since their anionic substructures follow bonding rules according to the valence concept. But there are also exceptions, which make the semiconductors especially interesting in terms of structure-property relationships. Although several Na-Sn-Pnictides with a variety of structural motives are known, up to this point no ternary compound in the Na-Sn-Bi system has been described. In this paper we present the Zintl-phase Na13Sn25.73Bi1.27 comprising a complex, open-framework structure of Sn atoms, with one mixed Sn/Bi site, hosting Na atoms. An additional Bi atom is loosely connected with only weak contacts to the framework filling a larger cavity within the network. According to band structure calculations of the two ordered variants with either full occupation of the mixed site with Sn or Bi, resulting in Na13Sn26Bi and Na13Sn24Bi3, respectively, both compounds are semiconductors with band gaps of 0.5 eV. A comparison of the band structures with the structurally related binary compounds Na5Sn13 and Na7Sn12 shows that only the perfectly charge balanced Na7Sn12 is a semiconductor whereas Na5Sn13 is metallic. The rather specific electronic situation in the ternary compound is traced back to the loosely bound Bi atom, which acts as a guest atom according to Bix@Na13Sn26-yBiy, with x=1 and y=0.27, capable to change its oxidation state and thus to uptake additional electrons allowing the system to be a semiconductor. Therefore, Na13Sn25.73Bi1.27 can be understood as a rare example of an open framework structure of Sn atoms comprising Bi atoms in the cavities.

Physical and Surface Chemical Analysis of High-Quality Antimicrobial Cotton Fabrics Functionalized with CuOx Grown In Situ from Different Copper Salts: Experimental and Theoretical Approach

The emergence of harmful microorganisms poses a public health challenge. Antimicrobial cotton textiles with semiconductor oxides offer a promising solution to mitigate pathogen spread. Here, we study the physicochemical interactions between copper oxides (CuOx) and cellulose in cotton fiber functionalized with these same oxides for antimicrobial properties. Fabrics were treated by an exhaust dyeing method using a 2% on-weight-of-fiber (owf) copper precursor with acetate, nitrate, and sulfate anions. Nonfunctionalized (NF) fabrics with a yellow hue turned reddish brown after the functionalization with CuOx. Copper (Cu) content in the functionalized fabrics increased by 27-40% compared to 0.009% in the NF fabric. The percentage of Cu exhaustion was higher with the acetate salt than nitrate and sulfate, resulting in darker fabrics according to colorimetry. XPS analysis of cotton suggests a chemical interaction between the hydroxyl groups of cellulose and CuOx. The nature and strength of potential interactions between Cu cations and the cellulose surface were investigated using the quantum theory of atoms in molecules and crystals. Based on topological parameters, the interaction between Cu and the hydroxyl groups of cellulose exhibits a covalent character. Furthermore, the XPS spectrum of functionalized fabrics exhibited peaks corresponding to Cu1+ and Cu2+ ions, assigned to the Cu2O and CuO phases, respectively. Electron diffraction patterns confirmed copper oxide crystalline phases, where Cu2O was indexed in the cuprite system and CuO in the tenorite system. Regarding morphology, no defined forms of CuOx were observed on the cotton surface, regardless of the salt used for treatment. Likewise, all fabrics functionalized with CuOx inhibited the growth of Escherichia coli and Pseudomonas aeruginosa strains by more than 99%. Therefore, cotton fabrics functionalized with a mixture of Cu2O and CuO have excellent antimicrobial properties that can be used in environments with a high bacterial load.

The Electron-Density Distribution of UCl4 and Its Topology from X-ray Diffraction

The chemistry of5 f ${5f}$ electrons in actinide complexes and materials is still poorly understood and represents a serious challenge and opportunity for experiment and theory. The study of the electron density distribution of the ground state of such systems through X-ray diffraction represents a unique opportunity to quantitatively investigate different chemical bonding interactions at once, but was considered "almost impossible" on heavy-atom systems, until very recently. Here, we present a combined experimental and theoretical investigation of the electron density distribution in UCl_4 crystals and comparison with the previously reported spin density distribution from polarized neutron diffraction. All approaches provide a consistent picture in terms of electron and spin density distribution, and chemical bond characterization. More importantly, the synergy between experiments and quantum-mechanical calculations allows to highlight the remarkable sensitivity of X-ray diffraction to5 f ${5f}$ electrons in materials.

Structure, morphology and surface properties of α-lactose monohydrate in relation to its powder properties

The particulate properties of α-lactose monohydrate (αLMH), an excipient and carrier for pharmaceuticals, is important for the design, formulation and performance of a wide range of drug products. Here an integrated multi-scale workflow provides a detailed molecular and inter-molecular (synthonic) analysis of its crystal morphology, surface chemistry and surface energy. Predicted morphologies are validated in 3D through X-ray diffraction (XCT) contrast tomography. Interestingly, from aqueous solution the fastest growth is found to lie along the b-axis, i.e. the longest unit cell dimension of the αLMH crystal structure reflecting the greater opportunities for solvation on the prism compared to the capping faces leading to the former's slower relative growth rates. The tomahawk morphology reflects the presence of β-lactose which asymmetrically binds to the capping surfaces creating a polar morphology. The crystal lattice energy is dominated by van der Waals interactions (between lactose molecules) with electrostatic interactions contributing the remainder. Predicted total surface energies are in good agreement with those measured at high surface coverage by inverse gas chromatography, albeit their dispersive contributions are found to be higher than those measured. The calculated surface energies of crystal habit surfaces are not found to be significantly different between different crystal surfaces, consistent with αLMH's known homogeneous binding to drug molecules when formulated. Surface energies for different morphologies reveals that crystals with the elongated crystal morphologies have lower surface energies compared to those with a triangular or tomahawk morphologies, correlating well with literature data that the surface energies of the lactose carriers are inversely proportional to their aerosol dispersion performance.

Substantial oxygen loss and chemical expansion in lithium-rich layered oxides at moderate delithiation

Delithiation of layered oxide electrodes triggers irreversible oxygen loss, one of the primary degradation modes in lithium-ion batteries. However, the delithiation-dependent mechanisms of oxygen loss remain poorly understood. Here we investigate the oxygen non-stoichiometry in Li1.18-xNi0.21Mn0.53Co0.08O2-δ electrodes as a function of Li content by using cycling protocols with long open-circuit voltage steps at varying states of charge. Surprisingly, we observe substantial oxygen loss even at moderate delithiation, corresponding to 2.5, 4.0 and 7.6 ml O2 per gram of Li1.18-xNi0.21Mn0.53Co0.08O2-δ after resting at upper capacity cut-offs of 135, 200 and 265 mAh g-1 for 100 h. Our observations suggest an intrinsic oxygen instability consistent with predictions of high oxygen activity at intermediate potentials versus Li/Li+. In addition, we observe a large chemical expansion coefficient with respect to oxygen non-stoichiometry, which is about three times greater than those of classical oxygen-deficient materials such as fluorite and perovskite oxides. Our work challenges the conventional wisdom that deep delithiation is a necessary condition for oxygen loss in layered oxide electrodes and highlights the importance of calendar ageing for investigating oxygen stability.

Advancing dynamic quantum crystallography: enhanced models for accurate structures and thermodynamic properties

X-ray diffraction (XRD) has evolved significantly since its inception, becoming a crucial tool for material structure characterization. Advancements in theory, experimental techniques, diffractometers and detection technology have led to the acquisition of highly accurate diffraction patterns, surpassing previous expectations. Extracting comprehensive information from these patterns necessitates different models due to the influence of both electron density and thermal motion on diffracted beam intensity. While electron-density modelling has seen considerable progress [e.g. the Hansen-Coppens multipole model and Hirshfeld Atom Refinement (HAR)], the treatment of thermal motion has remained largely unchanged. We have developed a novel method that combines the strengths of the advanced charge-density models [Aspherical Atom Models (AAMs), such as HAR or the Transferable Aspherical Atom Model (TAAM)] and the thermal motion model (normal modes refinement, NoMoRe). We denote this approach AAM_NoMoRe, wherein instead of refining routine anisotropic displacement parameters (ADPs) against single-crystal X-ray diffraction data, we refine the frequencies obtained from periodic density functional theory (DFT) calculations. In this work, we demonstrate the effectiveness of this model by presenting its application to model compounds, such as alanine, xylitol, naphthalene and glycine polymorphs, highlighting the influence of our method on the H-atom positions and shape of their ADPs, which are comparable with neutron data. We observe a significant decrease in the similarity index for H-atom ADPs after AAM_NoMoRe in comparison to only AAM, aligning more closely with neutron data. Due to the use of aspherical form factors (AAM), our approach demonstrates better fitting performance, as indicated by consistently lower wR2 values compared to the Independent Atom Model (IAM) refinement and a significant decrease compared to the traditional NoMoRe model. Furthermore, we present the estimation of a key thermodynamic property, namely, heat capacity, and demonstrate its alignment with experimental calorimetric data.

Tracking anharmonic oscillations in the structure of β-1,3-diacetylpyrene

A recently discovered β polymorph of 1,3-diacetylpyrene has turned out to be a prominent negative thermal expansion material, with a linear thermal expansion coefficient of -199 (6) MK-1 at room temperature. Its unique properties can be linked to anharmonic oscillations in the crystal structure that can be attributed to several weak C-H...O interactions. The onset and development of anharmonic effects have been successfully tracked over a wide (90-390 K) temperature range using single-crystal X-ray diffraction. Experimental data of sufficient quality combined with Hirshfeld atom refinement of the crystal structures enabled a quantitative analysis of elusive anharmonic effects within the Gram-Charlier formalism. This example highlights that quantum crystallography tools can and should be applied in structural analysis even for data collected at high temperatures as well as of standard (∼0.8 Å) resolution.

Space-Confinement and in Situ Reduction of Pt with 1T-MoS2 for Exceptional Hydrogen Evolution Reaction in Simulated Seawater

Efficient catalysts for hydrogen generation from seawater are essential for advancing clean energy technologies. In this study, we present a straightforward method for producing Pt nanoparticles enclosed within metallic 1T-phase MoS2 nanosheets on graphite paper as a promising catalyst for the hydrogen evolution reaction (HER). The resulting 14.3 wt % Pt-MoS2 nanosheets demonstrate an ultralow onset potential of 65.6 mV vs the reversible hydrogen electrode (RHE) and a minimal Tafel slope of 64 mV/dec with remarkable stability and durability in simulated seawater, offering comparable catalytic performance to the 40 wt % Pt/C commercial catalyst at a lower cost. This exceptional hydrogen production is attributed to the robust reducing ability of 1T-phase MoS2 and the confinement of Pt nanoparticles within the MoS2 interlayers and nanosheets. Our findings highlight the significance of this approach in developing practical and sustainable electrocatalysts for seawater splitting. This research represents a crucial step toward a greener and more sustainable future, leveraging innovative catalyst design strategies for clean energy production.

Non-equilibrium transport in polymer mixed ionic-electronic conductors at ultrahigh charge densities

Conducting polymers are mixed ionic-electronic conductors that are emerging candidates for neuromorphic computing, bioelectronics and thermoelectrics. However, fundamental aspects of their many-body correlated electron-ion transport physics remain poorly understood. Here we show that in p-type organic electrochemical transistors it is possible to remove all of the electrons from the valence band and even access deeper bands without degradation. By adding a second, field-effect gate electrode, additional electrons or holes can be injected at set doping states. Under conditions where the counterions are unable to equilibrate in response to field-induced changes in the electronic carrier density, we observe surprising, non-equilibrium transport signatures that provide unique insights into the interaction-driven formation of a frozen, soft Coulomb gap in the density of states. Our work identifies new strategies for substantially enhancing the transport properties of conducting polymers by exploiting non-equilibrium states in the coupled system of electronic charges and counterions.

Contrasting conformational behaviors of molecules XXXI and XXXII in the seventh blind test of crystal structure prediction

Accurate modeling of conformational energies is key to the crystal structure prediction of conformational polymorphs. Focusing on molecules XXXI and XXXII from the seventh blind test of crystal structure prediction, this study employs various electronic structure methods up to the level of domain-local pair natural orbital coupled cluster singles and doubles with perturbative triples [DLPNO-CCSD(T1)] to benchmark the conformational energies and to assess their impact on the crystal energy landscapes. Molecule XXXI proves to be a relatively straightforward case, with the conformational energies from generalized gradient approximation (GGA) functional B86bPBE-XDM changing only modestly when using more advanced density functionals such as PBE0-D4, ωB97M-V, and revDSD-PBEP86-D4, dispersion-corrected second-order Møller-Plesset perturbation theory (SCS-MP2D), or DLPNO-CCSD(T1). In contrast, the conformational energies of molecule XXXII prove difficult to determine reliably, and variations in the computed conformational energies appreciably impact the crystal energy landscape. Even high-level methods such as revDSD-PBEP86-D4 and SCS-MP2D exhibit significant disagreements with the DLPNO-CCSD(T1) benchmarks for molecule XXXII, highlighting the difficulty of predicting conformational energies for complex, drug-like molecules. The best-converged predicted crystal energy landscape obtained here for molecule XXXII disagrees significantly with what has been inferred about the solid-form landscape experimentally. The identified limitations of the calculations are probably insufficient to account for the discrepancies between theory and experiment on molecule XXXII, and further investigation of the experimental solid-form landscape would be valuable. Finally, assessment of several semi-empirical methods finds r2SCAN-3c to be the most promising, with conformational energy accuracy intermediate between the GGA and hybrid functionals and a low computational cost.

Coupled Perturbed Approach to Dual Basis Sets for Molecules and Solids. II: Energy and Band Corrections for Periodic Systems

When trying to reach convergence of quantum chemical calculations toward the complete basis set limit, crystalline solids generally prove to be more challenging than molecules. This is due both to the closer packing of atoms─hence, to linear dependencies─and to the problematic behavior of Ewald techniques used for dealing with the infinite character of Coulomb sums. Thus, a dual basis set approach is even more desirable for periodic systems than for molecules. In such an approach, the self-consistent procedure is implemented in a small basis set, and the effect of the enlargement of the basis set is estimated a posteriori. In this paper, we extend to crystalline solids our previous coupled perturbed dual basis set approach [J. Chem. Theory Comput. 2020, 16, 1, 340-353] in which the basis set enlargement is treated as a perturbation. Among the notable features of this approach are (i) the possibility of obtaining not only a correction to the energy but also to energy bands and electron density; (ii) the absence of a diagonalization step for the full Fock matrix in the large basis set; and (iii) the possibility of extrapolating low order perturbation energy corrections to infinite order. We also present here the first periodic implementation of the dual basis set method of Liang and Head-Gordon [J. Phys. Chem. A 2004, 108, 3206-3210]. The effectiveness of both approaches is, then, compared on a small, but representative, set of solids.

Tailoring superstructure units for improved oxygen redox activity in Li-rich layered oxide battery's positive electrodes

The high-voltage oxygen redox activity of Li-rich layered oxides enables additional capacity beyond conventional transition metal (TM) redox contributions and drives the development of positive electrode active materials in secondary Li-based batteries. However, Li-rich layered oxides often face voltage decay during battery operation. In particular, although Li-rich positive electrode active materials with a high nickel content demonstrate improved voltage stability, they suffer from poor discharge capacity. Here, via physicochemical and electrochemical measurements, we investigate the correlation between oxygen redox activity and superstructure units in Li-rich layered oxides, specifically the fractions of LiMn6 and Ni4+-stabilized LiNiMn5 within the TM layer. We prove that an excess of LiNiMn5 hinders the extraction/insertion of lithium ions during Li metal coin cell charging/discharging, resulting in incomplete oxygen redox activity at a cell potential of about 3.3 V. We also demonstrate that lithium content adjustment could be a beneficial approach to tailor the superstructure units. Indeed, we report an improved oxygen redox reversibility for an optimized Li-rich layered oxide with fewer LiNiMn5 units.

Exploring Interatomic Electron Transfer and Metal-Ligand Binding Mechanism in Trimethylenemethane Iron Tricarbonyl: Insights from Potentials per Electron and Corresponding Force Density Fields

This study employs an analysis of the per-electron potentials and the superposition of the electrostatic and kinetic force fields, Fes(r) and Fk(r), and the gradients of the potential energy and one-electron densities to investigate the binding mechanism in trimethylenemethane iron tricarbonyl complex (TMM)Fe(CO)3. Our approach permits the delineation of the "ligand-binding" force field generated by the metal nucleus but partially operating within the ligand atoms. A mechanical rationale for metal-ligand interactions is thus presented: In the corresponding area, the attractive force Fes(r) provides the backdrop against which the homotropic static force F (r) and the heterotropic kinetic force Fk(r) exert attractive and repulsive influences, respectively, toward the metal nucleus on a portion of the electrons belonging to the ligand atoms. This area thus represents electron sharing, which emerges as a quantum chemical response against the metal-to-ligand electron transfer. It has been demonstrated that the response is facilitated by the decreased potential energy density in the vicinity of the interatomic surface. Our findings indicate that the polar coordination bonds in (TMM)Fe(CO)3 exhibit notable quantum chemical responses. However, the previously described nonbonded contact also features an unexpectedly pronounced response, despite the absence of a bond path. It can be proposed that the unforeseen response is a consequence of the formation of the 18-electron, closed valence shell, rather than an indication of the establishment of an organometallic chemical bond.

The Non-Centrosymmetric Borate Hydride Sr4Ba3(BO3)3.83H2.5

Sr4Ba3(BO3)3.83H2.5, as the second compound to combine borate and hydride ions, has been synthesized by a mechanochemical synthesis route. The structure has been elucidated by synchrotron X-ray and neutron diffraction and determined to crystallize in the non-centrosymmetric space group P63mc (186) with the cell parameters a=10.87762(15) Å and c=6.98061(11) Å. A detailed investigation of the compound by vibrational spectroscopy in combination with Density Functional Theory calculations reveals the disordered nature of the structure and proves the presence of both borate and hydride ions. Electronic band structure calculations predict a large band gap of 7.1 eV. Hydride states are predicted at the topmost valence band, which agrees well with earlier reported heteroanionic hydrides. We hereby were able to successfully apply previously synthetic and analytical schemes to introduce another member of the rare compounds that contain complex oxoanions simultaneously with hydride ions.

Luminescence Thermochromism of a Noncluster Copper Iodide Complex

Hybrid copper(I) halide materials are currently attracting significant attention due to their exceptional luminescence properties, offering great potential for the development of multifunctional emissive materials with, in addition, eco-friendly features. A binuclear copper iodide complex, based on the [Cu2I2L4] motif with phosphite derivatives as ligands, has been synthesized and structurally characterized. Photophysical investigations indicate that this complex displays luminescence thermochromic properties, which are characterized by a temperature-dependent change in the relative intensity of two emission bands. The high-contrast luminescence thermochromism, with an important color variation from purple to cyan, is ascribed to the thermal equilibrium of two different excited states. While thermochromism is relatively known for multimetallic complexes, the perfectly controlled thermochromism of the studied compound is unprecedented for a binuclear complex. From theoretical investigations, this original feature is due to the coordination of phosphite ligands, which induces a specific energy layout of the complex, presenting vacant orbitals of varying nature. This single-component, dual-emissive binuclear complex, displaying relevant sensitivity temperature response, presents great potential for luminescence ratiometric thermometry applications. This study underlines the relevance of the ligand engineering strategy in developing original, emissive, and sustainable copper-based materials.

Mechanical Tuning of Fluorescence Lifetime and Bandgap in an Elastically Flexible Molecular Semiconductor Crystal

Despite having superior transport properties, lack of mechanical flexibility is a major drawback of crystalline molecular semiconductors as compared to their polymer analogues. Here single crystals of an organic semiconductor are reported that are not only flexible but exhibit systematic tuning of bandgaps, fluorescence lifetime, and emission wavelengths upon elastically bending. Spatially resolved fluorescence lifetime imaging and confocal fluorescence microscopy reveals systematic trends in the lifetime decay across the bent crystal region along with shifts in the emission wavelength. From the outer arc to the inner arc of the bent crystal, a significant decrease in the lifetime of ≈1.9 ns is observed, with a gradual bathochromic shift of ≈10 nm in the emission wavelength. For the crystal having a bandgap of 2.73 eV, the directional stress arising from bending leads to molecular reorientation effects and variations in the extent of intermolecular interactions- which are correlated to the lowering of bandgap and the evolution of the projected density of states. The systematic changes in the interactions quantified using electron density topological analysis in the compressed inner arc and elongated outer arc region are correlated to the non-radiative decay processes, thus rationalizing the tuning of fluorescence lifetime.

Na3Ge2P3: A Zintl Phase Featuring [P3Ge-GeP3] Dimers as Building Blocks

Recently, ternary lithium phosphidotetrelates have attracted interest particularly due to their high ionic conductivities, while corresponding sodium and heavier alkali metal compounds have been less investigated. Hence, we report the synthesis and characterization of the novel ternary sodium phosphidogermanate Na3Ge2P3, which is readily accessible via ball milling of the elements and subsequent annealing. According to single crystal X-ray structure determination, Na3Ge2P3 crystallizes in the monoclinic space group P21/c (no. 14.) with unit cell parameters of a = 7.2894(6) Å, b = 14.7725(8) Å, c = 7.0528(6) Å, β = 106.331(6)° and forms an unprecedented two-dimensional polyanionic network in the b/c plane of interconnected [P3Ge-GeP3] building units. The system can also be interpreted as differently sized ring structures that interconnect and form a two-dimensional network. A comparison with related ternary compounds from the corresponding phase system as well as with the binary compound GeP shows that the polyanionic network of Na3Ge2P3 resembles an intermediate step between highly condensed cages and discrete polyanions, which highlights the structural variety of phosphidogermanates. The structure is confirmed by 23Na- and 31P-MAS NMR measurements and Raman spectroscopy. Computational investigation of the electronic structure reveals that Na3Ge2P3 is an indirect band gap semiconductor with a band gap of 2.9 eV.

Strong Magnetic Exchange Interactions and Delocalized Mn-O States Enable High-Voltage Capacity in the Na-Ion Cathode P2-Na0.67[Mg0.28Mn0.72]O2

The increased capacity offered by oxygen-redox active cathode materials for rechargeable lithium- and sodium-ion batteries (LIBs and NIBs, respectively) offers a pathway to the next generation of high-gravimetric-capacity cathodes for use in devices, transportation and on the grid. Many of these materials, however, are plagued with voltage fade, voltage hysteresis and O2 loss, the origins of which can be traced back to changes in their electronic and chemical structures on cycling. Developing a detailed understanding of these changes is critical to mitigating these cathodes' poor performance. In this work, we present an analysis of the redox mechanism of P2-Na0.67[Mg0.28Mn0.72]O2, a layered NIB cathode whose high capacity has previously been attributed to trapped O2 molecules. We examine a variety of charge compensation scenarios, calculate their corresponding densities of states and spectroscopic properties, and systematically compare the results to experimental data: 25Mg and 17O nuclear magnetic resonance (NMR) spectroscopy, operando X-band and ex situ high-frequency electron paramagnetic resonance (EPR), ex situ magnetometry, and O and Mn K-edge X-ray Absorption Spectroscopy (XAS) and X-ray Absorption Near Edge Spectroscopy (XANES). Via a process of elimination, we suggest that the mechanism for O redox in this material is dominated by a process that involves the formation of strongly antiferromagnetic, delocalized Mn-O states which form after Mg2+ migration at high voltages. Our results primarily rely on noninvasive techniques that are vital to understanding the electronic structure of metastable cycled cathode samples.

Probing the range of applicability of structure- and energy-adjusted QM/MM link bonds III: QM/MM MD simulations of solid-state systems at the example of layered carbon structures

The previously introduced workflow to achieve an energetically and structurally optimized description of frontier bonds in quantum mechanical/molecular mechanics (QM/MM)-type applications was extended into the regime of computational material sciences at the example of a layered carbon model systems. Optimized QM/MM link bond parameters at HSEsol/6-311G(d,p) and self-consistent density functional tight binding (SCC-DFTB) were derived for graphitic systems, enabling detailed investigation of specific structure motifs occurring in graphene-derived structures v i a quantum-chemical calculations. Exemplary molecular dynamics (MD) simulations in the isochoric-isothermic (NVT) ensemble were carried out to study the intercalation of lithium and the properties of the Stone-Thrower-Wales defect. The diffusivity of lithium as well as hydrogen and proton adsorption on a defective graphene surface served as additional example. The results of the QM/MM MD simulations provide detailed insight into the applicability of the employed link-bond strategy when studying intercalation and adsorption properties of graphitic materials.

Prediction of metal-free Stoner and Mott-Hubbard magnetism in triangulene-based two-dimensional polymers

Ferromagnetism and antiferromagnetism require robust long-range magnetic ordering, which typically involves strongly interacting spins localized at transition metal atoms. However, in metal-free systems, the spin orbitals are largely delocalized, and weak coupling between the spins in the lattice hampers long-range ordering. Metal-free magnetism is of fundamental interest to physical sciences, unlocking unprecedented dimensions for strongly correlated materials and biocompatible magnets. Here, we present a strategy to achieve strong coupling between spin centers of planar radical monomers in π-conjugated two-dimensional (2D) polymers and rationally control the orderings. If the π-states in these triangulene-based 2D polymers are half-occupied, then we predict that they are antiferromagnetic Mott-Hubbard insulators. Incorporating a boron or nitrogen heteroatom per monomer results in Stoner ferromagnetism and half-metallicity, with the Fermi level located at spin-polarized Dirac points. An unprecedented antiferromagnetic half-semiconductor is observed in a binary boron-nitrogen-centered 2D polymer. Our findings pioneer Stoner and Mott-Hubbard magnetism emerging in the electronic π-system of crystalline-conjugated 2D polymers.

Theoretical Study on the Correlation between Open-Shell Electronic Structures and Third-Order Nonlinear Optical Properties in One-Dimensional Chains of π-Radicals

This paper theoretically investigated the correlation between the open-shell electronic structure and third-order nonlinear optical (NLO) properties of one-dimensional (1D) stacked chains of π-radicals. By employing the finite N-mer models consisting of methyl or phenalenyl radicals with different stacking distances, we evaluated the average and standard deviation of diradical characters yi for N-mer models of π-radicals (yav and ySD). Then, we estimated these diradical characters at the limit of N → ∞. These y-based indices were helpful in discussing the correlation between the open-shell electronic structures and the second hyperpolarizability per dimer at the limit N → ∞, γ∞ for the 1D chains with stacking distance alternation (SDA). The calculated γ∞ values and the polymer/dimer ratio γ∞/γ(N = 2) were enhanced significantly when both the stacking distance and SDA are small. We also found that the spin-unrestricted long-range-corrected (LC-)UBLYP method with the range-separating parameter μ = 0.47 bohr-1 well reproduced the trend of γ∞ of this type of 1D chain estimated at the spin-unrestricted coupled-cluster levels. The present study is expected to contribute to establishing the design guidelines for future high-performance open-shell molecular NLO materials.

First-Principles Linear Combination of Atomic Orbitals Calculations of K2SiF6 Crystal: Structural, Electronic, Elastic, Vibrational and Dielectric Properties

The results of first-principles calculations of the structural, electronic, elastic, vibrational, dielectric and optical properties, as well as the Raman and infrared (IR) spectra, of potassium hexafluorosilicate (K2SiF6; KSF) crystal are discussed. KSF doped with manganese atoms (KSF:Mn4+) is known for its ability to function as a phosphor in white LED applications due to the efficient red emission from Mn⁴⁺ activator ions. The simulations were performed using the CRYSTAL23 computer code within the linear combination of atomic orbitals (LCAO) approximation of the density functional theory (DFT). For the study of KSF, we have applied and compared several DFT functionals (with emphasis on hybrid functionals) in combination with Gaussian-type basis sets. In order to determine the optimal combination for computation, two types of basis sets and four different functionals (three advanced hybrid-B3LYP, B1WC, and PBE0-and one LDA functional) were used, and the obtained results were compared with available experimental data. For the selected basis set and functional, the above-mentioned properties of KSF were calculated. In particular, the B1WC functional provides us with a band gap of 9.73 eV. The dependencies of structural, electronic and elastic parameters, as well as the Debye temperature, on external pressure (0-20 GPa) were also evaluated and compared with previous calculations. A comprehensive analysis of vibrational properties was performed for the first time, and the influence of isotopic substitution on the vibrational frequencies was analyzed. IR and Raman spectra were simulated, and the calculated Raman spectrum is in excellent agreement with the experimental one.

Concurrent oxygen evolution reaction pathways revealed by high-speed compressive Raman imaging

Transition metal oxides are state-of-the-art materials for catalysing the oxygen evolution reaction (OER), whose slow kinetics currently limit the efficiency of water electrolysis. However, microscale physicochemical heterogeneity between particles, dynamic reactions both in the bulk and at the surface, and an interplay between particle reactivity and electrolyte makes probing the OER challenging. Here, we overcome these limitations by applying state-of-the-art compressive Raman imaging to uncover concurrent bias-dependent pathways for the OER in a dense, crystalline electrocatalyst, α-Li2IrO3. By spatially and temporally tracking changes in stretching modes we follow catalytic activation and charge accumulation following ion exchange under various electrolytes and cycling conditions, comparing our observations with other crystalline catalysts (IrO2, LiCoO2). We demonstrate that at low overpotentials the reaction between water and the oxidized catalyst surface is compensated by bulk ion exchange, as usually only found for amorphous, electrolyte permeable, catalysts. At high overpotentials the charge is compensated by surface redox active sites, as in other crystalline catalysts such as IrO2. Hence, our work reveals charge compensation can extend beyond the surface in crystalline catalysts. More generally, the results highlight the power of compressive Raman imaging for chemically specific tracking of microscale reaction dynamics in catalysts, battery materials, or memristors.

Covalent Organic Frameworks in Computational Design of Second-Harmonic Generation Materials: Role of Tetrel Atoms and Their Interactions

Modern approaches to the design of nonlinear optical materials often rely on computational techniques. Here, we discuss the effects of the variation in the center tetrel atoms, Tt = C, Si, or Ge, in a series of covalent organic frameworks of the COF-102 family. The effects of halogen substitution, Hal = Cl, Br, or I on intramolecular tetrel bonding are also discussed. The characteristics of the calculated electron density have been implemented to describe the features of the electron distribution around the central fragment involving a tetrahedral tetrel atom. The effect of the central Tt atom leads to a dramatic change in the character of electron delocalization on the Tt-Car bond with aromatic rings. The location of the halogen atom at the ortho-position of the aromatic ring leads to the formation of tetrel bonds, halogen bonds, or other noncovalent interactions. The changes in the second-order electric susceptibility χ(2) have been studied in order to describe the strength of nonlinear optical properties within the periodic couple-perturbed Kohn-Sham approach. A counterintuitive trend for the χ(2) decrease is observed upon substitution of H > Cl > Br > I at the ortho-position of the phenyl ring. This is due to the corresponding elongation of the Tt-Car bond.

Strength of London Dispersion Forces in Organic Structure Directing Agent-Zeolite Assemblies

Herein, we study the London dispersion forces between organic structure directing agents (OSDAs)-here tetraalkyl-ammonium or -phosphonium molecules-and silica zeolite frameworks (FWs). We demonstrate that the interaction energy for these dispersion forces is correlated to the number of H atoms in OSDAs, irrespective of the structures of OSDAs or FWs, and of variations in charges and thermal motions. All calculations considered-DFT-D3 and BOMD undertaken by us, and molecular mechanics from an accessible database-led to the same trend. The mean energy of these dispersion forces is ca. -2 kcal.mol-1 per H for efficient H-O contacts.

Wavy Graphene Nanoribbons Containing Periodic Eight-Membered Rings for Light-Emitting Electrochemical Cells

Precision graphene nanoribbons (GNRs) offer distinctive physicochemical properties that are highly dependent on their geometric topologies, thereby holding great potential for applications in carbon-based optoelectronics and spintronics. While the edge structure and width control has been a popular strategy for engineering the optoelectronic properties of GNRs, non-hexagonal-ring-containing GNRs remain underexplored due to synthetic challenges, despite offering an equally high potential for tailored properties. Herein, we report the synthesis of a wavy GNR (wGNR) by embedding periodic eight-membered rings into its carbon skeleton, which is achieved by the A2B2-type Diels-Alder polymerization between dibenzocyclooctadiyne (6) and dicyclopenta[e,l]pyrene-5,11-dione derivative (8), followed by a selective Scholl reaction of the obtained ladder-type polymer (LTP) precursor. The obtained wGNR, with a length of up to 30 nm, has been thoroughly characterized by solid-state NMR, FT-IR, Raman, and UV/Vis spectroscopy with the support of DFT calculations. The non-planar geometry of wGNR efficiently prevents the inter-ribbon π-π aggregation, leading to photoluminescence in solution. Consequently, the wGNR can function as an emissive layer for organic light-emitting electrochemical cells (OLECs), offering a proof-of-concept exploration in implementing luminescent GNRs into optoelectronic devices. The fast-responding OLECs employing wGNR will pave the way for advancements in OLEC technology and other optoelectronic devices.

Codoped germanene with 3p and 4p elements elements

CONTEXT

The relentless need for new materials to be used in electronic devices has opened new research directions in materials science. One of them involves using two-dimensional materials, among which there is current interest in using germanene. The heteroatom doping of germanene has been proposed as a possible approach to fine-tuning its electronic properties. However, this procedure is complicated because locating the dopants with a specific arrangement is challenging, thus achieving reproducibility. To avoid this problem, we propose the codoping of germanene to understand if dopants prefer to be agglomerated as observed for graphene or if they prefer to adopt a random disposition. Herein, we employed first-principles calculations to study 21 codoped germanene systems with one 3p (Al, Si, P, and S) and one 4p (Ga, As, and Se) element. Our results indicate that in the cases of AlP, AlS, GaP, GaS, GaAs, and GaSe codoped germanene, the dopants show a tendency to be located in specific lattice positions. The ortho disposition of dopants is preferred for AlP, AlS, GaP and GaS codoped germanene and their 4p counterparts GaAs and GaSe codoped germanene, and the materials showed interesting electronic properties making them suitable to develop germanene-based electronic materials.

METHODS

We utilized the M06-L, HSE06 methods accompanied by the 6-31G* basis sets to perform periodic boundary conditions calculations as implemented in Gaussian 09. The unit cells were sampled employing 100 k-points for geometry optimizations and 2000 k-points for electronic properties The ultrafine grid was employed. Results were visualized employing Gaussview 5.0.1. In addition to this, we performed B3LYP-D3 periodic calculations as implemented in CRYSTAL17.

Quantitative localisation of titanium in the framework of titanium silicalite-1 using anomalous X-ray powder diffraction

One of the biggest obstacles to developing better zeolite-based catalysts is the lack of methods for quantitatively locating light heteroatoms on the T-sites in zeolites. Titanium silicalite-1 (TS-1) is a Ti-bearing zeolite-type catalyst commonly used in partial oxidation reactions with H2O2, such as aromatic hydroxylation and olefin epoxidation. The reaction mechanism is controlled by the configuration of titanium sites replacing silicon in the zeolite framework, but these sites remain unknown, hindering a fundamental understanding of the reaction. This study quantitatively determines heteroatoms within the zeolite-type framework using anomalous X-ray powder diffraction (AXRD) and the changes in the titanium X-ray scattering factor near the Ti K-edge (4.96 keV). Two TS-1 samples, each with approximately 2 Ti atoms per unit cell, were examined. Half of the titanium atoms are primarily split between sites T3 and T9, with the remainder dispersed among various T-sites within both MFI-type frameworks. One structure showed significant non-framework titanium in the micropores of a more distorted lattice. In both samples, isolated titanium atoms were more prevalent than dinuclear species, which could only potentially arise at site T9, but with a significant energy penalty and were not detected.

Modulation of triplet quantum coherence by guest-induced structural changes in a flexible metal-organic framework

Quantum sensing has the potential to improve the sensitivity of chemical sensing by exploiting the characteristics of qubits, which are sensitive to the external environment. Modulation of quantum coherence by target analytes can be a useful tool for quantum sensing. Using molecular qubits is expected to provide excellent sensitivity due to the proximity of the sensor to the target analyte. However, many molecular qubits are used at cryogenic temperatures, and how to make molecular qubits respond to specific analytes remains unclear. Here, we propose a material design in which the coherence time changes in response to a variety of analytes at room temperature. We used the photoexcited triplet, which can be initialized at room temperature, as qubits and introduce them to a metal-organic framework that can flexibly change its pore structure in response to guest adsorption. By changing the local molecular density around the triplet qubits by adsorption of a specific analyte, the mobility of the triplet qubit can be changed, and the coherence time can be made responsive.

Toward the Chemical Structure of Diborane: Electronic Force Density Fields, Effective Electronegativity, and Internuclear Turning Surface Properties

The chemical structure of diborane was elucidated through the superposition of the vector fields of the electron density gradient ∇ρ(r), the electrostatic force Fes(r), and the kinetic force Fk(r), together with the analysis of the cumulative charges of the atoms and pseudoatoms delimited in the aforementioned fields. It was proposed that the Fk-pseudoatomic charge could be employed as a metric for quantifying the ionic component of a related atomic charge. The electron permeability across an internuclear turning surface─specifically, the zero-flux surface in Fk(r)─was characterized by probing it through mapping the total static potential φem(r). The conceptualization of post hoc electronegativity was presented for consideration. Our analysis revealed that the ordinary B-H and bent B-μ-H bonds in diborane demonstrate the polar covalent character with minor contributions of the ionic component. The former bond exhibits a greater electron permeability through the internuclear turning surface, indicating a stronger tendency for electron sharing between the corresponding nucleus-dominated regions. The electron density accumulation along the bent B-μ-H bond path diverges from the minimum action trajectories of the forces Fes(r) and Fk(r). This phenomenon can be associated with the structural strain within the angled, three-center two-electron bonding B-μ-H-B. The internuclear B···B paths were identified in Fes(r) and Fk(r), in contrast to ∇ρ(r). This fact, in conjunction with a pronounced electron permeability through the mutual turning surface between the two boron nuclei, implies a certain degree of electron exchange between the boron-dominated pseudoatomic regions. Furthermore, the anomalous [B-]H···μ-H intermolecular polar interactions were described between the strongly negatively charged hydrogen atoms in the monoclinic crystalline β-phase of diborane. In fact, the ionic contributions to the charges of the hydrogen atoms are shown to be relatively small.

Large Number of Direct or Pseudo-Direct Band Gap Semiconductors among A3TrPn2 Compounds with A = Li, Na, K, Rb, Cs; Tr = Al, Ga, In; Pn = P, As

Due to the high impact of semiconductors with respect to many applications for electronics and energy transformation, the search for new compounds and a deep understanding of the structure-property relationship in such materials has a high priority. Electron-precise Zintl compounds of the composition A3TrPn2 (A = Li - Cs, Tr = Al - In, Pn = P, As) have been reported for 22 possible element combinations and show a large variety of different crystal structures comprising zero-, one-, two- and three-dimensional polyanionic substructures. From Li to Cs, the compounds systematically lower the complexity of the anionic structure. For an insight into possible crystal-structure band-structure relations for all compounds (experimentally known or predicted), their band structures, density of states and crystal orbital Hamilton populations were calculated on a basis of DFT/PBE0 and SVP/TZVP basis sets. All but three (Na3AlP2, Na3GaP2 and Na3AlAs2) compounds show direct or pseudo-direct band gaps. Indirect band gaps seem to be linked to one specific structure type, but only for Al and Ga compounds. Arsenides show smaller band gaps than phosphides due to weaker Tr-As bonds. The bonding situation was confirmed by a Mullikan analysis, and most states close to the Fermi level were assigned to non-bonding orbitals.

Structural and Electronic Properties of the Magnetic and Nonmagnetic X0.125Mg0.875B2 (X = Nb, Ni, Fe) Materials: A DFT/HSE06 Approach to Investigate Superconductor Behavior

MgB2 material has a simple composition and structure that is well-reported and characterized. This material has been widely studied and applied in the last 20 years as a superconductor in wire devices and storage material for H in the hydride form. MgB2 doped with transition metals improves the superconductor behavior, such as the critical temperature (T cs) or critical current (J sc) for the superconducting state. The results obtained in this manuscript indicate that Nb-, Fe-, and Ni-doping in the Mg site leads to a contraction of the unit cell through the spin polarization on the electronic resonance of the boron layer. Fe and Ni transition metals doping perturb the electronic resonance because of stronger dopant-boron bonds. The unpaired electrons are transferred from 3d orbitals to the empty 2p z orbitals of the boron atoms, locating α electrons in the σ bonds and β electrons in the π orbitals. The observed influence of magnetic dopants on MgB2 enables the proposal of an electronic mechanism to explain the spin polarization of boron hexagonal rings.

Boosted Photocatalytic Activities of Ag2CrO4 through Eu3+-Doping Process

Ag2CrO4 is a representative member of a family of Ag-containing semiconductors with highly efficient visible-light-driven responsive photocatalysts. The doping process with Eu3+ is known to effectively tune their properties, thus opening opportunities for investigations and application. Here, we report the enhancement of the photocatalytic activity and stability of Ag2CrO4 by introducing Eu3+cations. The structural, electronic, and photocatalytic properties of Ag2CrO4:xEu3+ (x = 0, 0.25, 0.5, 1%) synthesized using the coprecipitation method were systematically discussed, and their photodegradation activity against rhodamine B (RhB), ciprofloxacin hydrochloride monohydrate (CIP), and 4-nitrophenol (4-NP) was evaluated. Structural analyses reveal a short-range symmetry breaking in the Ag2CrO4 lattice after Eu3+ doping, influencing the material morphology, size, and electronic properties. XPS analysis confirmed the incorporation of Eu3+ and alteration of the surface oxygen species. Furthermore, photoluminescence measurements indicated that the doping process was responsible for reducing recombination processes. The sample doped with 0.25% Eu3+ exhibited superior photocatalytic performance compared to pure Ag2CrO4. Scavenger experiments revealed an increase in the degradation via •OH reactive species for the sample doped with 0.25% Eu3+. DFT calculations provided atomic-scale insights into the structural and electronic changes induced by the Eu3+ doping process in the Ag2CrO4 host lattice. This study confirms that Eu3+ doping alters the band structure, enabling different degradation paths and boosting the separation/transfer of photogenerated charges, thereby improving the overall photocatalytic performance.

Charge Density Study of Two-Electron Four-Center Bonding in a Dimer of Tetracyanoethylene Radical Anions as a Benchmark for Two-Electron Multicenter Bonding

The dimer of the tetracyanoethylene (TCNE) radical anions represents the simplest and the best studied case of two-electron multicenter covalent bonding (2e/mc or pancake bonding). The model compound, N-methylpyridinium salt of TCNE•-, is diamagnetic, meaning that the electrons in two contiguous radicals are paired and occupy a HOMO orbital which spans two TCNE•- radicals. Charge density in this system is studied as a benchmark for comparison of charge densities in other pancake-bonded radical systems. Two electrons from two contiguous radicals indeed form a bonding electron pair, which is distributed between two central ethylene groups in the dimer, i.e., between four carbon atoms. The topology of electron density reveals two bond critical points between the central ethylene groups in the dimer, with maximum electron density of 0.185 e Å-3; the corresponding theoretical value is 0.118 e Å-3.