Pairs Of Atoms Research Articles

Room-Temperature Chemoselective Hydrogenation of Nitroarene Over Atomic Metal-Nonmetal Catalytic Pair.

Constructing atomic catalytic pair emerges as an attractive strategy to achieve better catalytic performance. Herein, an atomic Ir1─P1/NPG catalyst with asymmetric Ir─N2P1 sites that delivers superb activity and selectivity for hydrogenation of various functionalized nitrostyrene is reported. In the hydrogenation reaction of 3-nitrostyrene, Ir1─P1/NPG (NPG refers to N, P-codoped graphene) shows a turnover frequency of 1197h-1, while the reaction cannot occur over Ir1/NG (NG refers to N-doped graphene). Compared to Ir1/NG, the charge density of the Ir site in Ir1─P1/NPG is greatly elevated, which is conducive to H2 dissociation. Moreover, as revealed by density functional theory calculations and poisoning experiments, the P site in Ir1─P1/NPG is found able to bind nitrostyrene, while the neighboring Ir site provides H to reduce the nitro group in chemoselective hydrogenation of nitrostyrene. This work offers a successful example of establishing atomic catalytic pair for driving important chemical reactions, paving the way for the development of more advanced catalysts to further improve the catalytic performance.

Rydberg-Rydberg interaction strengths and dipole blockade radii in the presence of Förster resonances.

Achieving a substantial blockade radius is crucial for developing scalable and efficient quantum communication and computation. In this theoretical study, we present the enhancement of the Rydberg blockade radius by utilizing Förster resonance. This phenomenon occurs when the energy difference between two initial Rydberg states closely matches that between the corresponding final Rydberg states, giving rise to a resonant energy transfer process. We employ quantum defect theory to numerically calculate the 87Rb-87Rb Rydberg atomic pair, enabling us to accurately estimate the van der Waals interaction. Our investigation reveals that when the principal quantum numbers of two Rydberg states differ only slightly, the Förster transition is rarely able to achieve a large blockade radius. However, in cases where the principal quantum numbers differ significantly, we substantially improve the Rydberg blockade radius. Most notably, we identify transition channels exhibiting an extensive blockade radius, surpassing 50 μm. This significant increase in the blockade radius enables larger-scale quantum operations and advances quantum technologies, with broad implications for achieving long-range quantum entanglement and robust quantum processes.

Estimation of Two Component Activities of Binary Liquid Alloys by the Pair Potential Energy Containing a Polynomial of the Partial Radial Distribution Function

An investigation of partial radial distribution functions and atomic pair potentials within a system has established that the existing potential functions are rooted in the assumption of a static arrangement of atoms, overlooking their distribution and vibration. In this study, Hill’s proposed radial distribution function polynomials are applied for the pure gaseous state to a binary liquid alloy to derive the pair potential energy. The partial radial distribution functions of 36 binary liquid alloy from literatures were used to obtain the binary model parameters of four thermodynamic models for validation. Results show that the regular solution model (RSM) and molecular interaction volume model (MIVM) outperform other models when the asymmetric method calculates the partial radial distribution function. RSM demonstrates an average SD of 0.078 and an ARD of 32.2%. Similarly, MIVM exhibits an average SD of 0.095 and an average ARD of 32.2%. Wilson model yields an average SD of 0.124 and an average ARD of 226%. Nonrandom two-liquid (NRTL) model exhibits an average SD of 0.225 and an average ARD of 911%. On applying the partial radial distribution function symmetry method, MIVM and RSM outperform the other models, with an average SD of 0.143 and an average ARD of 165.9% for MIVM. RSM yields an average SD of 0.117 and an average ARD of 208.3%. Wilson model exhibits average values of 0.133 and 305.6% for SD and ARD, respectively. NRTL model shows an average SD of 0.200 and an average ARD of 771.8%. Based on this result, the influence of the symmetry degree on the thermodynamic model is explored by examining the symmetry degree as defined by the experimental activity curves of the two components.

Fine-tuned photochromic WO3-x thin films: A detailed study from structural analysis to UV photo-sensing application

The oxygen substoichiometry of as-prepared WO3 (tungsten trioxide) nano-powders (NPs) from a polyol process was tuned via peptization of the NPs in aqueous solutions of different Cr2O72− oxidizing concentrations. The as-synthesized materials have been characterized by X-ray scattering (XRD and PDF), transmission electron microscopy (TEM), X-ray photoelectron (XPS), and UV-VIS photochromic activity. The local atomic structure of WO3-X was investigated using total scattering atomic pair distribution function (PDF) analysis based on X-ray total scattering data collected on powder at ambient conditions. The PDF analysis confirms that the crystal structure of all studied samples can be described in terms of very small crystallites with a P21/n space-group monoclinic framework but with anomalous unit cell distortion parameters, indicating that small crystallite sizes resulted in a larger monoclinic distortion (as measured by the beta angle of the unit cell). The nanometer dimension of the crystallites combined as well as the oxygen-tungsten stoichiometric ratio control, are key features for optimized photochromic properties. Moreover, we present the fabrication of a WO3-x thin film based UV photosensor, which was carried out on silica glass substrates via the dip-coating method. The obtained films exhibited a UV photoresponse and photoelectric characteristics at 5 V bias voltages able to detect very low UV doses, inferior to 10 W/m2. The photo-detection measurements prove the usability of our device as a UV photodetector with a good responsivity of 0.37 A/W and external quantum efficiency of more than 100% even at a very low power density (9.2 W/m2) of UV illumination.

Probing Molecular Packing of Amorphous Pharmaceutical Solids Using X-ray Atomic Pair Distribution Function and Solid-State NMR.

The structural investigation of amorphous pharmaceuticals is of paramount importance in comprehending their physicochemical stability. However, it has remained a relatively underexplored realm primarily due to the limited availability of high-resolution analytical tools. In this study, we utilized the combined power of X-ray pair distribution functions (PDFs) and solid-state nuclear magnetic resonance (ssNMR) techniques to probe the molecular packing of amorphous posaconazole and its amorphous solid dispersion at the molecular level. Leveraging synchrotron X-ray PDF data and employing the empirical potential structure refinement (EPSR) methodology, we unraveled the existence of a rigid conformation and discerned short-range intermolecular C-F contacts within amorphous posaconazole. Encouragingly, our ssNMR 19F-13C distance measurements offered corroborative evidence supporting these findings. Furthermore, employing principal component analysis on the X-ray PDF and ssNMR data sets enabled us to gain invaluable insights into the chemical nature of the intermolecular interactions governing the drug-polymer interplay. These outcomes not only furnish crucial structural insights facilitating the comprehension of the underlying mechanisms governing the physicochemical stability but also underscore the efficacy of synergistically harnessing X-ray PDF and ssNMR techniques, complemented by robust modeling strategies, to achieve a high-resolution exploration of amorphous structures.

The Equilibrium Molecular Structure of Cyclic (Alkyl)(Amino) Carbene Copper(I) Chloride via Gas-Phase Electron Diffraction and Quantum Chemical Calculations.

Copper-centered carbene-metal-halides (CMHs) with cyclic (alkyl)(amino) carbenes (CAACs) are bright phosphorescent emitters and key precursors in the synthesis of the highly promising class of the materials carbene-metal-amides (CMAs) operating via thermally activated delayed fluorescence (TADF). Aiming to reveal the molecular geometry for CMH phosphors in the absence of the intermolecular contacts, we report here the equilibrium molecular structure of the (CAAC)Cu(I)Cl (1) molecule in the gas-phase. We demonstrate that linear geometry around a copper atom shows no distortions in the ground state. The structure of complex 1 has been determined using the electron diffraction method, supported by quantum chemical calculations with RI-MP2/def2-QZVPP level of theory and compared with the crystal structure determined by X-ray diffraction analysis. Mean vibrational amplitudes, uij,h1, and anharmonic vibrational corrections (rij,e • rij,a) were calculated for experimental temperature T = 20 °C, using quadratic and cubic force constants, respectively. The quantum theory of atoms in molecules (QTAIM) and natural bond order (NBO) analysis of wave function at MN15/def2TZVP level of theory revealed two Cu…H, three H…H, and one three-center H…H…H bond paths with bond critical points. NBO analysis also revealed three-center, four-electron hyperbonds, (3c4e), [π(N-C) nπ(Cu) ↔ nπ(N) π(N-Cu)], or [N-C: Cu ↔ N: C-Cu] and nπ(Cu) → π(C-N)* hyperconjugation, that is the delocalization of the lone electron pair of Cu atom into the antibonding orbital of C-N bond.

Optimal subradiant spin wave exchange in dipole-coupled atomic ring arrays

The subwavelength array of quantum emitters provides an ideal platform for exploring rich many-body dynamics, such as super- and subradiance. In this paper, we explore the dynamics of spin wave exchange between two dipole-coupled atomic ring arrays. Subradiant spin waves lead to low-loss and high efficiency of ring-to-ring transfer. The optimal subradiant spin wave exchange occurs at appropriate separations between coplanar rings, despite the fact that the energy transfer efficiency is monotonically enhanced (in the regime ) as the rings’ separation decreases. However, the spin wave will scatter due to the dephasing mechanism of close-by atom pairs, as the separation of two rings is too small. With the increase in the number of atoms on the ring, the subradiant shielding effect also strengthens, leading to a shorter distance for the transfer of spin waves. We investigate the rotation of one of the rings and find that the optimal spin wave exchange corresponds to the scenario where the line connecting the two nearest atoms of the two rings aligns with the center of the circle. Moreover, we study the influence of transition dipole moment orientations on the effective interaction between two atomic rings. We observe that there is a critical point where the effective interaction strength changes dramatically owing to the cooperative effect of the subwavelength atomic array. We believe that our results could be important for quantum information processing based on atomic arrays.

Role of vacancies in structural thermalization of binary and high-entropy alloys

Vacancy assisted atomic self-diffusion is a major structural thermalization mechanism in bulk metal alloys. Depending on alloy composition, the local atomic environments might stabilize vacancies to such extent that the vacancies become trapped and the atomic self-diffusion part of the thermalization process stalls. The consequence is that such alloys get kinetically trapped in disordered structures. In this study, we investigate equimolar AgAu, CuPt, AgPdPtIr, and AgAuCuPdPt alloy thermalizing using Metropolis Monte Carlo simulations in two approaches, one where the alloy structure changes through vacancy migration and one where the structure changes by swapping atomic pairs. By comparing the two approaches, we find that the vacancy is less effective at thermalizing alloys with more elements (i.e. AgPdPtIr and AgAuCuPdPt), more heterogeneous configurational internal energy distributions (i.e. CuPt and AgPdPtIr), and strong interactions between certain elements, e.g. Ir-Ir interactions in AgPdPtIr. In the case of AgPdPtIr, the vacancy cannot thermalize Ir-Ir neighbors even when the vacancy is mobile, because the vacancy has difficulty breaking individual Ir-Ir pairs apart.

Unveiling enhanced electron-mediated peroxymonosulfate activation for degradation of emerging organic pollutants

The electron transfer pathway activated by peroxymonosulfate (PMS) has garnered significant attention for the removal of emerging organic pollutants from water. However, overcoming the two-step energy barriers involved in electron transport across reaction interfaces presents a formidable challenge. To surmount the two-step energy barriers of pollutant-catalyst and catalyst-PMS, a catalyst with nano-island structure was developed, forming efficient ternary catalytic interfaces with PMS and pollutants. The presence of atomic pairs within the catalyst punched through the electron transport channels, resulting in a pseudo-first-order kinetic rate of 2.06 min−1 for bisphenol A, which was 5.1 times higher than that of the control sample. The electronic coupling of atomic pairs exerted a profound impact on the splitting of d-orbitals, effectively elevating the d-orbital unoccupancy and reducing the two-step energy barriers encountered by electrons from pollutants to catalysts, and subsequently to PMS, which promoted efficient degradation of pollutants. Furthermore, through the association of two-step energy barrier, the feasibility of utilizing the orbital interaction as a descriptor of the degradation rate by electron-mediated PMS activation was demonstrated. Additionally, the intermediates generated through electron transfer pathway exhibited a lower risk of bioaccumulation. This work inspires insights into the electron-mediated mechanism of multinary catalytic interface reactions.

Highly accessible dual-metal atomic pairs for enhancing oxygen redox reaction in zinc−air batteries

The bifunctional oxygen electrocatalyst acts as a key component for zinc−air batteries; however, the design of economically-feasible bifunctional electrocatalysts showing outstanding functionality and durability remains challenging. Herein, we report the preparation of homogeneously scattered dual Fe−Ni atomic pairs stabilized in porous N-doped carbon matrix with a hierarchically porous nanoarchitecture (denoted as FeNi-NHC), wherein the atomically isolated bimetallic configuration is verified by combinative investigation of microscopy, spectroscopy, and theoretical computations. As an oxygen electrocatalyst in a basic electrolyte, FeNi-NHC exhibits an exceptional activity, achieving an outstanding half-wave potential (0.934 V vs. RHE) for oxygen reduction reaction, and a small overpotential for oxygen evolution reaction (254 mV at 10 mA cm-2). Furthermore, the zinc–air battery constructed with FeNi-NHC catalyst delivers an excellent functionality featuring a high maximum power density (126 mW cm-2) and insignificant activity decay after 200 charge−discharge cycles. Theoretical computations further reveal that the interaction effect of neighboring metal atoms in the bimetallic Fe−Ni sites energetically promotes the catalytic process by reducing the overall reaction barriers via optimization of adsorption−desorption behaviors.

Synthesis, Crystal Structure Analyses, and Antibacterial Evaluation of the Cobalt(II) Complex with Sulfadiazine-Pyrazole Prodrug

The complex [Co(L)(H2O)4](NO3)2 of (E)-4-(2-(3-methyl-5-oxo-1-(pyridin-2-yl)-1H-pyrazol-4(5H)-ylidene)hydrazinyl)-N-(pyrimidin-2-yl)benzenesulfonamide (L) was synthesized via the self-assembly technique. Its molecular and supramolecular structures were analyzed using FTIR, elemental analyses, and single-crystal X-ray diffraction, as well as Hirshfeld calculations. This complex crystallized in the triclinic space group P1¯ with Z = 2. The crystallographic asymmetric unit comprised one complex cation and two nitrate counter anions. This complex had distorted octahedral geometry around the Co(II) ion. Numerous intermolecular interactions affecting the molecular packing of this complex were conformed using Hirshfeld investigations. The most significant contacts for the cationic inner sphere [Co(L)(H2O)4]2+ were O···H (38.8%), H···H (27.8%), and N···H (9.9%). On the other hand, the main interactions for the counter NO3¯ ions were the O···H (79.6 and 77.8%), O···N (8.0%), and O···C (9.1%). A high propensity for making interactions for each atom pair in the contacts O…H, N…C, N…H, and C…C was revealed by enrichment ratio values greater than 1. The antibacterial efficacy of the complex and the free ligand were assessed. The free ligand had higher antibacterial activity (MIC = 62.5–125 µg/mL) than the [Co(L)(H2O)4](NO3)2 complex (MIC ≥ 250 µg/mL) versus all the studied bacteria.

Hirshfeld Surface Analysis and Density Functional Theory Calculations of 2-Benzyloxy-1,2,4-triazolo[1,5-a] quinazolin-5(4H)-one: A Comprehensive Study on Crystal Structure, Intermolecular Interactions, and Electronic Properties

This study employs a comprehensive computational analysis of the 2-benzyloxy-1,2,4-triazolo[1,5-a] quinazolin-5(4H)-one (ID code: CCDC 834498) to explore its intermolecular interactions, surface characteristics, and crystal structure. Utilizing the Hirshfeld surface technique and Crystal Explorer 17.5, the study maps the Hirshfeld surfaces for a detailed understanding of atom pair close contacts and interaction types. The study also investigates the compound’s electronic and optical characteristics using Frontier Molecular Orbital (FMO) analysis and Global Reactivity Parameters (GRPs). The compound is identified as electron-rich with strong electron-donating and accepting potential, indicating its reactivity and stability. Its band gap suggests Nonlinear Optical (NLO) attributes. The Molecular Electrostatic Potential (MEP) map reveals charge distribution across the compound’s surface. The computational methods’ reliability is validated by the low Mean Absolute Error (MAE) and Mean Squared Error (MSE) in the comparison of experimental and theoretical bond lengths and angles.

Boosting the Proton‐coupled Electron Transfer via Fe−P Atomic Pair for Enhanced Electrochemical CO2 Reduction

AbstractSingle‐atom catalysts exhibit superior CO2‐to‐CO catalytic activity, but poor kinetics of proton‐coupled electron transfer (PCET) steps still limit the overall performance toward the industrial scale. Here, we constructed a Fe−P atom paired catalyst onto nitrogen doped graphitic layer (Fe1/PNG) to accelerate PCET step. Fe1/PNG delivers an industrial CO current of 1 A with FECO over 90 % at 2.5 V in a membrane‐electrode assembly, overperforming the CO current of Fe1/NG by more than 300 %. We also decrypted the synergistic effects of the P atom in the Fe−P atom pair using operando techniques and density functional theory, revealing that the P atom provides additional adsorption sites for accelerating water dissociation, boosting the hydrogenation of CO2, and enhancing the activity of CO2 reduction. This atom‐pair catalytic strategy can modulate multiple reactants and intermediates to break through the inherent limitations of single‐atom catalysts.

Boosting the Proton-coupled Electron Transfer via Fe-P Atomic Pair for Enhanced Electrochemical CO2 Reduction.

Single-atom catalysts exhibit superior CO2 -to-CO catalytic activity, but poor kinetics of proton-coupled electron transfer (PCET) steps still limit the overall performance toward the industrial scale. Here, we constructed a Fe-P atom paired catalyst onto nitrogen doped graphitic layer (Fe1 /PNG) to accelerate PCET step. Fe1 /PNG delivers an industrial CO current of 1 A with FECO over 90 % at 2.5 V in a membrane-electrode assembly, overperforming the CO current of Fe1 /NG by more than 300 %. We also decrypted the synergistic effects of the P atom in the Fe-P atom pair using operando techniques and density functional theory, revealing that the P atom provides additional adsorption sites for accelerating water dissociation, boosting the hydrogenation of CO2 , and enhancing the activity of CO2 reduction. This atom-pair catalytic strategy can modulate multiple reactants and intermediates to break through the inherent limitations of single-atom catalysts.

On the molecular structure modelling of gamma graphyne and armchair graphyne nanoribbon via reverse degree-based topological indices

ABSTRACT Reverse degree-based topological indices (RDTIs) are applied to analyze the structural properties of molecules such as gamma graphyne and armchair graphyne nanoribbons. RDTIs provide valuable information about the connectivity patterns of atoms within a molecule, aiding in understanding its chemical and physical properties. For gamma graphyne and armchair graphyne nanoribbons, RDTIs would involve calculating the contributions from various atom pairs based on the degree differences between them. These indices consider the reverse order in which degrees are subtracted. RDTIs capture important aspects of molecular structure, including branching, degree distribution, and connectivity. Using RDTIs, one can assess the complexity, stability, and other characteristics of gamma graphyne and armchair graphyne nanoribbons. This paper focus on two structures made from hexagonal honeycomb graphite lattices, like gamma graphyne, and armchair graphyne nanoribbons. The methodology used in this study is First and second reverse Gourava indices, hyper first and second reverse Gourava indices, reverse multiplicative sum connectivity Gourava index, and reverse multiplicative product connectivity Gourava. Furthermore, these indices play a vital role in quantitative structure–property relationships and offer insights into the behaviour and reactivity of these unique molecular structures. Further research and computational analysis of RDTIs will deepen our understanding of these fascinating carbon-based materials.

Atomic-Level Description of Chemical, Topological, and Surface Morphology Aspects of Oxide Film Grown on Polycrystalline Aluminum during Thermal Oxidation—Reactive Molecular Dynamics Simulations

Oxidation results in the formation of an oxide film whose properties and structure can be tailored by controlling the oxidation conditions. Reactive molecular dynamics simulations were performed to study thermal oxidation of polycrystalline Al substrates as a function of O2 density and temperature. The structural, chemical, and topological aspects of polycrystalline Al (poly-Al) substrates and oxide films formed upon oxidation were studied. The studies were supported by surface topography and morphology analyses before and after oxidation. An analysis of Al–O atomic pair distribution showed the development of long-range order in the oxide films grown upon exposure to low-density (0.005 g/cm3) and high-density (0.05 g/cm3) O2 gas. The long-range order was more apparent for the high-density environment, as the oxide films formed in low-density O2 gas did not fully cover the poly-Al surface. The dominance of over-coordinated polyhedral units in a tightly packed structure was indicative of medium- and long-range atomic order in the oxide films. The two-phase structure of the oxide was found in the films, with a crystalline phase at the metal/oxide interface and an amorphous phase at the oxide/O2 interface. The combination with topological analyses supported the conclusions of the chemical analysis and enabled us to capture an amorphous-to-crystalline phase transformation in the oxide films with increasing oxygen density and temperature. An important effect of Al surface roughness before oxidation on the behavior of the metal/oxide interface and on the oxide film structure was observed.

Molecular Dynamics of Artificially Pair-Decoupled Systems: An Accurate Tool for Investigating the Importance of Intramolecular Couplings.

We propose a numerical technique to accurately simulate the vibrations of organic molecules in the gas phase, when pairs of atoms (or, in general, groups of degrees of freedom) are artificially decoupled, so that their motion is instantaneously decorrelated. The numerical technique we have developed is a symplectic integration algorithm that never requires computation of the force but requires estimates of the Hessian matrix. The theory we present to support our technique postulates a pair-decoupling Hamiltonian function, which parametrically depends on a decoupling coefficient α ∈ [0, 1]. The closer α is to 0, the more decoupled the selected atoms. We test the correctness of our numerical method on small molecular systems, and we apply it to study the vibrational spectroscopic features of salicylic acid at the Density Functional Theory ab initio level on a fitted potential. Our pair-decoupled simulations of salicylic acid show that decoupling hydrogen-bonded atoms do not significantly influence the frequencies of stretching modes, but enhance enormously the out-of-plane wagging and twisting motions of the hydroxyl and carboxyl groups to the point that the carboxyl and hydroxyl groups may overcome high potential energy barriers and change the salicylic acid conformation after a short simulation time. In addition, we found that the acidity of salicylic acid is more influenced by the dynamical couplings of the proton of the carboxylic group with the carbon ring than with the hydroxyl group.

Insight into coupled Ni-Co dual-metal atom catalysts for efficient synergistic electrochemical CO2 reduction

The development of highly active, selective, and stable electrocatalysts can facilitate the effective implementation of electrocatalytic CO2 conversion into fuels or chemicals for mitigating the energy crisis and climate problems. Therefore, it is necessary to achieve the goal through reasonable material design based on the actuality of the operational active site at the molecular scale. Inspired by the stimulating synergistic effect of coupled heteronuclear metal atoms, a novel Ni-Co atomic pairs configuration (denoted as NiN3©CoN3-NC) active site was theoretically screened out for improving electrochemical CO2 reduction reaction (CO2RR). The structure of NiN3©CoN3-NC was finely regulated by adjusting Zn content in the precursors Zn/Co/Ni-zeolite imidazolate frameworks (Zn/Co/Ni-ZIFs) and pyrolysis temperature. The structural features of NiN3©CoN3-NC were systematically confirmed by aberration-corrected HAADF-STEM coupled with 3D atom-overlapping Gaussian-function fitting mapping, XAFS, and XRD. The results of theoretical calculations reveal that the synergistic effect of Ni-Co atomic pairs can effectively promote the *COOH intermediate formation and thus the overall CO2RR kinetic was improved, and also restrained the competitive hydrogen evolution reaction. Due to the attributes of Ni-Co atomic pairs configuration, the developed NiN3©CoN3-NC with superior catalytic activity, selectivity, and durability, with a high turnover frequency of 2265 h−1 at −1.1 V (vs. RHE) and maximum Faradaic efficiency of 97.7% for CO production. This work demonstrates the great potential of DACs as highly efficient catalysts for CO2RR, provides a useful strategy to design heteronuclear DACs, exploits the synergistic effect of multiple metal sites to facilitate complex CO2RR catalytic reactions, and inspires more efforts to develop the potential of DACs in various fields.

Chromium Metal Nanoparticles, Their Reactivity and Reactions

AbstractZerovalent chromium nanoparticles (2.2±0.2 nm in size) are prepared in the liquid phase (THF) by reduction of CrCl2 with lithium naphthalenide ([LiNaph]). The deep black Cr(0) nanoparticle suspensions in THF are colloidally and chemically highly stable. On the other hand, the Cr(0) nanoparticles are highly reactive, e. g., when in contact to O2, H2O, or other oxidizing agents. To probe the reactivity of the Cr(0) nanoparticles in the liquid phase near room temperature (50–80 °C), they are reacted with different coordinatively demanding, N−H, S−H or O−H acidic reactants. This includes the amines 2,2′‐dipyridylamine (HDPA), 2‐(1H‐imidazol‐2‐yl)pyridine (HImPy) and carbazole (HCbz), the thiol 2‐mercaptopyridine (HMPy), and benzoic acid (HBz) as a carboxylate. As a result, the five novel compounds [Cr(DPA)3], [Cr(ImPy)3] ⋅ HImPy, [Cr(MPy)3] ⋅ 0.5 Tol (Tol: toluene), [Na2Cr(Cbz)4(THF)3], and [Cr2(Bz)4(THF)2] are obtained. [Cr(DPA)3] and [Cr(ImPy)3] ⋅ HImPy show Cr(III) coordinated by nitrogen only; [Cr(MPy)3] ⋅ 0.5 Tol shows a coordination of Cr(III) by both N and S atoms. [Na2Cr(Cbz)4(THF)3] and [Cr2(Bz)4(THF)2] contain Cr(II) and exhibit an infinite chain‐like structure and pairs of chromium atoms with fourfold binding.

Towards the extraction of the crystal cell parameters from pair distribution function profiles.

The approach based on atomic pair distribution function (PDF) has revolutionized structural investigations by X-ray/electron diffraction of nano or quasi-amorphous materials, opening up the possibility of exploring short-range order. However, the ab initio crystal structural solution by the PDF is far from being achieved due to the difficulty in determining the crystallographic properties of the unit cell. A method for estimating the crystal cell parameters directly from a PDF profile is presented, which is composed of two steps: first, the type of crystal cell is inferred using machine-learning approaches applied to the PDF profile; second, the crystal cell parameters are extracted by means of multivariate analysis combined with vector superposition techniques. The procedure has been validated on a large number of PDF profiles calculated from known crystal structures and on a small number of measured PDF profiles. The lattice determination step has been benchmarked by a comprehensive exploration of different classifiers and different input data. The highest performance is obtained using the k-nearest neighbours classifier applied to whole PDF profiles. Descriptors calculated from the PDF profiles by recurrence quantitative analysis produce results that can be interpreted in terms of PDF properties, and the significance of each descriptor in determining the prediction is evaluated. The cell parameter extraction step depends on the cell metric rather than its type. Monometric, dimetric and trimetric cells have top-1 estimates that are correct 40, 20 and 5% of the time, respectively. Promising results were obtained when analysing real nanocrystals, where unit cells close to the true ones are found within the top-1 ranked solution in the case of monometric cells and within the top-6 ranked solutions in the case of dimetric cells, even in the presence of a crystalline impurity with a weight fraction up to 40%.