Least-squares Refinement Research Articles

Exploring the anti-diabetic activity of 2,6-diamino-4-chloropyrimidinium-hydrogen oxalate conjugates: Synthesis, crystal structure, quantum computational, drug-likeness, molecular docking and dynamics simulation

Inhibiting carbohydrate-hydrolyzing enzyme has been considered as an effective approach for controlling starch digestion and postprandial blood glucose level. The aim of this study, the salt molecule was prepared to identify potentially effective compound against diabetic activity and discover the inhibitory mechanism of the targeted enzyme, which is determined by In-silico techniques. And also perform the quantum chemical calculation to provide insights about the internal motions of the molecule at the atomic level. The 2,6-diamino-4-chloropyrimidinium-hydrogen oxalate (C4H6ClN4+. C2HO4-) was newly synthesized molecule, which is detailly discussed in this present work. The title compound has been confirmed by single-crystal X-ray diffraction studies, and this structure was refined by the least-square refinement method. The crystal compound exhibited the P-1 space group (centrosymmetric) and the following unit cell parameters: a = 5.5778(6)Å, b = 9.6687(10)Å, c = 9.9144(10)Å, α = 116.342(1) °, β = 92.610(1) °, γ = 106.370(1) °, Z = 2. The molecular structure is stabilized by the networks of N–H···O, O–H···O, C–H···O, and N–H···N hydrogen bond interactions. The Hirshfeld surface (HS) analysis and fingerprint plots revealed strong intermolecular interaction between the molecules. The structural optimization, frontier molecular orbital (FMO), molecular reactivity, molecular electrostatic potential (MEP), and mulliken atomic charges were generated by the density functional theory (DFT) calculated at B3LYP/6-311G++ (d,p) theory level. Drug-likeness and physicochemical properties were predicted. The molecular docking analysis was showed a binding energy of −8.96 kcal/mol within the active site of alpha-amylase, which is responsible for anti-diabetic activity. The protein-ligand complex stability was verified using molecular dynamics studies with 100 ns.

Linking solid-state phenomena via energy differences in `archetype crystal structures'

Categorization underlies understanding. Conceptualizing solid-state structures of organic molecules with `archetype crystal structures' bridges established categories of disorder, polymorphism and solid solutions and is herein extended to special position and high-Z′ structures. The concept was developed in the context of disorder modelling [Dittrich, B. (2021). IUCrJ, 8, 305–318] and relies on adding quantum chemical energy differences between disorder components to other criteria as an explanation as to why disorder – and disappearing disorder – occurs in an average structure. Part of the concept is that disorder, as probed by diffraction, affects entire molecules, rather than just the parts of a molecule with differing conformations, and the finding that an R·T energy difference between disorder archetypes is usually not exceeded. An illustrative example combining disorder and special positions is the crystal structure of oestradiol hemihydrate analysed here, where its space-group/subgroup relationship is required to explain its disorder of hydrogen-bonded hydrogen atoms. In addition, we show how high-Z′ structures can also be analysed energetically and understood via archetypes: high-Z′ structures occur when an energy gain from combining different rather than overall alike conformations in a crystal significantly exceeds R·T, and this finding is discussed in the context of earlier explanations in the literature. Twinning is not related to archetype structures since it involves macroscopic domains of the same crystal structure. Archetype crystal structures are distinguished from crystal structure prediction trial structures in that an experimental reference structure is required for them. Categorization into archetype structures also has practical relevance, leading to a new practice of disorder modelling in experimental least-squares refinement alluded to in the above-mentioned publication.

Modeling Complex Ligands for High Oxidation State Catalysis: Titanium Hydroamination with Unsymmetrical Ligands.

A method for modeling high oxidation state catalysts is used on precatalysts with unsymmetrical and symmetrical bidentate ligands to get a more detailed understanding of how changes to ancillary ligands affect the hydroamination of alkynes catalyzed by titanium. To model the electronic donor ability, the ligand donor parameter (LDP) was used, and to model the steric effects, percent buried volume (% Vbur) was employed. For the modeling study, 7 previously unpublished unsymmetrical Ti(XX')(NMe2)2 precatalysts were prepared, where XX' is a chelating ligand with pyrrolyl/indolyl linkages. The rates of these unsymmetrical and 10 previously reported symmetrical precatalysts were used with the model kobs = a + b(LDP)1 + c(LDP)2 + d(% Vbur)1 + e(% Vbur)2, where a-e were found through least-squares refinement. The model suggests that (1) the two attachment points of the bidentate ligand XX' are in different environments on the metal (e.g., axial and equatorial in a trigonal bipyramidal or square pyramidal structure), (2) the position of the unsymmetrical ligand on the metal is determined by the electronics of the ligand rather than the sterics, and (3) that one side of the chelating ligand's electronics strongly influences the rate, while the other side's sterics more strongly influences the rate. From these studies, we were able to generate catalysts fitting to this model with rate constants larger than the fastest symmetrical catalyst tested.

Verification labels for rovibronic quantum-state energy uncertainties

Transition wavenumbers contained in line-by-line rovibronic databases can be compromised by errors of various nature. When left undetected, these errors may result in incorrect quantum-state energies, potentially compromising a large number of derived spectroscopic data. Spectroscopic networks treat the complete set of line-by-line spectroscopic data as a large graph, and through a least-squares refinement the measured line positions are converted into empirical quantum-state energies. Spectroscopic networks also offer a highly useful framework to develop mathematical tools helping to identify possible errors and conflicts within the dataset. For example, wavenumber errors can be detected by checking for violations of the law of energy conservation. This paper describes a new graph-theory tool, which results in so-called verification labels for the quantum states. Verification labels help to express the vulnerability of a calculated empirical energy value and its uncertainty against possible wavenumber errors, providing complementary information to simple statistical uncertainties.

MARVEL analysis of high-resolution rovibrational spectra of C O .

A set of empirical rovibrational energy levels, obtained through the MARVEL (measured active rotational-vibrational energy levels) procedure, is presented for the C O isotopologue of carbon dioxide. This procedure begins with the collection and analysis of experimental rovibrational transitions from the literature, allowing for a comprehensive review of the literature on the high-resolution spectroscopy of C O , which is also presented. A total of 60sources out of more than 750 checked provided 14,101uniquely measured and assigned rovibrational transitions in the wavenumber range of 579-13,735 cm . This is followed by a weighted least-squares refinement yielding the energy levels of the states involved in the measured transitions. Altogether 6318empirical rovibrational energies have been determined for C O . Finally, estimates have been given for the uncertainties of the empirical energies, based on the experimental uncertainties of the transitions. The detailed analysis of the lines and the spectroscopic network built from them, as well as the uncertainty estimates, all serve to pinpoint possible errors in the experimental data, such as typos, misassignment of quantum numbers, and misidentifications. Errors found in the literature data were corrected before including them in the final MARVEL dataset and analysis.

Background optimization of powder electron diffraction for implementation of the e-PDF technique and study of the local structure of iron oxide nanocrystals.

The local structural characterization of iron oxide nanoparticles is explored using a total scattering analysis method known as pair distribution function (PDF) (also known as reduced density function) analysis. The PDF profiles are derived from background-corrected powder electron diffraction patterns (the e-PDF technique). Due to the strong Coulombic interaction between the electron beam and the sample, electron diffraction generally leads to multiple scattering, causing redistribution of intensities towards higher scattering angles and an increased background in the diffraction profile. In addition to this, the electron-specimen interaction gives rise to an undesirable inelastic scattering signal that contributes primarily to the background. The present work demonstrates the efficacy of a pre-treatment of the underlying complex background function, which is a combination of both incoherent multiple and inelastic scatterings that cannot be identical for different electron beam energies. Therefore, two different background subtraction approaches are proposed for the electron diffraction patterns acquired at 80 kV and 300 kV beam energies. From the least-square refinement (small-box modelling), both approaches are found to be very promising, leading to a successful implementation of the e-PDF technique to study the local structure of the considered nanomaterial.

Synthesis, Crystal Structure, and Electrical and Magnetic Characterizations of the Monoclinic Compounds Ln3Mo4+xSi1–xO14 (Ln = La, Ce, Pr, and Nd; x = 0 and 0.35) Containing Mo3 Clusters and Mo2 Dimers

Powder samples of the new monoclinic compounds Ln3Mo4SiO14 (Ln = La, Ce, Pr, and Nd) and single crystals of Pr3Mo4.35Si0.65O14 were obtained by the solid-state reaction. The crystal structure of Pr3Mo4.35Si0.65O14 was determined by single-crystal X-ray diffraction. Pr3Mo4.35Si0.65O14 crystallizes in the monoclinic space group P21/n with unit-cell parameters a = 5.6361 (2) Å, b = 17.5814 (8) Å, c = 10.9883 (4) Å, and Z = 4. Full-matrix least-squares refinement on F2 using 7544 independent reflections for 203 refinable parameters results in R1 = 0.0359 and wR2 = 0.0831. The structure contains chains of Mo3O13 clusters and chains of edge-sharing MoO6 octahedra with alternately short (2.508 Å) and long (3.161 Å) Mo-Mo distances running parallel to the a axis that are separated by 8- or 10-coordinate Pr-O polyhedra. Magnetic susceptibility measurements on the Ln3Mo4SiO14 (Ln = La, Ce, Pr, and Nd) are in agreement with a trivalent state of the rare earths for the Ce, Pr, and Nd compounds, while that on the lanthanum compound confirms the presence of one unpaired electron per Mo3 as expected. Resistivity measurements on a single crystal show that Pr3Mo4.35Si0.65O14 is a small band gap semi-conductor.

An optimized single-crystal to polycrystal model of the neutron transmission of textured polycrystalline materials

The attenuation coefficient of textured materials presents a complex dependence on the preferred orientation with respect to the neutron beam. Presented here is an attenuation coefficient model to describe textured polycrystalline materials, based on a single-crystal to polycrystalline approach, aiming towards use in full-pattern least-squares refinements of wavelength-resolved transmission experiments. The model evaluates the Bragg contribution to the attenuation coefficient of polycrystalline materials as a combination of the Bragg-reflected component of a discrete number of imperfect single crystals with different orientations, weighted by the volume fraction of the corresponding component in the orientation distribution function. The proposed methodology is designed to optimize the number of single-crystal orientations involved in the calculation, considering the instrument resolution and the statistical uncertainty of the experimental transmission spectra. The optimization of the model is demonstrated through its application to experiments on calibration samples presenting random crystallographic textures, measured on two imaging instruments with different resolutions. The capability of the model to simulate textured samples in different orientations is shown with a copper sample used as a reference in texture studies of archaeological objects and a 316L stainless steel sample produced by laser powder-bed fusion. The ability of the model to predict the attenuation coefficient of polycrystalline textured materials on the basis of a reduced number of texture components opens the possibility of including it in a least-squares fitting routine to perform crystallographic texture analysis from wavelength-resolved transmission experiments.

Refinement of anomalous dispersion correction parameters in single-crystal structure determinations.

Correcting for anomalous dispersion is part of any refinement of an X-ray dif-fraction crystal structure determination. The procedure takes the inelastic scattering in the diffraction experiment into account. This X-ray absorption effect is specific to each chemical compound and is particularly sensitive to radiation energies in the region of the absorption edges of the elements in the compound. Therefore, the widely used tabulated values for these corrections can only be approximations as they are based on calculations for isolated atoms. Features of the unique spatial and electronic environment that are directly related to the anomalous dispersion are ignored, although these can be observed spectroscopically. This significantly affects the fit between the crystallographic model and the measured intensities when the excitation wavelength in an X-ray diffraction experiment is close to an element's absorption edge. Herein, we report on synchrotron multi-wavelength single-crystal X-ray diffraction, as well as X-ray absorption spectroscopy experiments which we performed on the mol-ecular compound Mo(CO)6 at energies around the molybdenum K edge. The dispersive (f') and absorptive (f'') terms of the anomalous dispersion can be refined as independent parameters in the full-matrix least-squares refinement. This procedure has been implemented as a new feature in the well-established OLEX2 software suite. These refined parameters are in good agreement with the independently recorded X-ray absorption spectrum. The resulting crystallographic models show significant improvement compared to those employing tabulated values.

Non-destructive characterization of the spatial variation of γ/γ′ lattice misfit in a single-crystal Ni-based superalloy by energy-resolved neutron imaging

Lattice misfit in nickel-based superalloys is one of the important microstructural parameters that control their mechanical properties, such as creep behaviour at high temperatures. Here, energy-resolved neutron imaging experiments are performed at a spallation neutron source to determine the spatial variation of lattice misfit on a second-generation nickel-based single-crystal superalloy specimen produced from a failed low-cycle fatigue specimen. The wavelength spectrum of the neutrons scattered by the specimen displays a large number of peaks, each corresponding to a spot in traditional Laue diffraction experiments. An analysis of the position and width of those Laue peaks in the transmission spectra allows determination of the lattice parameters of the γ and γ′ phases that compose the specimen, as well as the strain misfit and the misorientation between them. An analytical model is developed to describe the full wavelength pattern of Laue peaks arising from a specimen composed of two single crystals, and this model is used to perform least-squares refinements of the spectra measured at different positions of the specimen, with a spatial resolution of ∼500 × 500 µm. The local variations of the lattice parameter across the sample area were less than 4 mÅ for both phases, and the lattice misfit remains essentially constant at a value of 0.30 ± 0.03%, whilst the misorientation between the two phases is always smaller than 10′. By contrast, the relative misorientation between different parts of the specimen varies locally up to 1.5° on a scale of millimetres.

Site splitting at M3 in allanite-(Ce)

AbstractWe report the crystal structure of allanite-(Ce), with composition (Ca1.0REE0.9□0.1)Σ2.0(Al1.46Fe3+0.52Fe2+0.76Mg0.12Ti0.15)Σ3.01Si3O12(OH) from the Xinfeng rare earth element (REE)-bearing granite in Guangdong Province, China. It has the unit cell a = 8.9550(4) Å, b = 5.77875(16) Å, c = 10.2053(4) Å, β = 114.929(5)° and Z = 2 in space group P21/m and is characterised by site splitting at M3 into M3a and M3b, at a distance of 0.38(3) Å, which are occupied partially by Fe0.764Mg0.12 and Ti0.15, respectively. The structure was determined by single-crystal X-ray diffraction and refined with anisotropic full-matrix least-squares refinement on F2 to R1 = 2.82%, wR2 = 7.77% for 1856 independent reflections (8772 collected reflections). However, M3 splitting is not present in either ferriallanite-(Ce) or epidote, in which M3 is almost fully occupied either by Fe2+ or by Fe3+. Comparisons of bond lengths and volumes in cation polyhedra among allanite-(Ce), ferriallanite-(Ce) and epidote tend to indicate that the essential factor that facilitates site splitting of M3 in allanite-(Ce) is heterovalent substitution and occupation of a crystallographic site between Fe2+(Mg2+/Mn2+)–Al3+(Ti4+), a common phenomenon in minerals, such as the plagioclase series. Fine structure analysis of the M3 split model revealed that deformation of A2 is related closely to distorted M3, which is consistent with Fe2+ incorporation following REE substitution.

Crystal structure of the compound ScCo2Si2: single crystal investigation

For the first time, the complete single crystal structure study of the compound ScCo 2 Si 2 was performed. It belongs to the CeGa 2 Al 2 structure type, Pearson’s symbol tI 10,139, space group I 4/ mmm , lattice parameters a =3.7775(3) c =9.6208(11) Å. The compound was prepared by arc-melting of the initial elements with the purity of not less than 99.9 % under argon followed by annealing in silica tubes at 800 °C for 350 h. Single crystals for structural examination were selected under a microscope from the broken alloys obtained. X-ray diffraction data of one of the irregularly faceted single crystals obtained at a temperature of 300(2) K by means of single crystal X-ray diffractometer Bruker D8 Venture with monochromatized Mo K α-radiation. The structure is refined using the program SHELXL, version 2018/3 (full-matrix least-squares refinement with anisotropic atomic parameters), R 1 = 0,0247, wR 2 = 0,0614 for 57 unique reflections with I o > 2 σ(I o ) and 8 refined parameters. Coordinates of atoms are the following: 2Sc at 2 а 0 0 0; 4Co at 4 d 0 1/2 1/4; 4Si at 4 e 0 0 z , z =0.3776(2). Coordination numbers of Sc, Co and Si atoms are 20, 12 and 9, respectively. The interatomic distances, with the exception of Co–Si, are longer than the sum of the metal radii of the corresponding atoms. Co–Si distances (2.2525(9) Å) are smaller than the sum of the radii of these atoms (2.42 Å) and indicate a significant interaction between Co and Si in the structure. Currently known three scandium ternary compounds ScM 2 Si 2 (M=Co, Ni, Cu) are members of complete series of compounds RM 2 Si 2 (R=rare earths) isotypic with CeGa 2 Al 2 . Crystal chemical analysis of scandium intermetallic compounds of stoichiometric composition ScM 2 X 2 (M= d -element; X= p -element) was performed. Scandium occupies a special place among rare earths and shows crystal chemical affinity both with rare earths and Zr and Hf. Keywords : ternary silicides, rare earth elements, single crystal, crystal structure.

On the incorporation of strontium into the crystal structure of bredigite: structural effects and phase transition

Sr-substitution in the crystal structure of bredigite has been studied in detail. Samples of a hypothetical solid-solution series with nominal composition Ca7-xSrxMg[SiO4]4 (x = 0, 2, …,7) have been prepared from sinter reactions in the temperature range between 1275 and 1325 °C and characterized using powder and single-crystal X-ray diffraction. Synthesis runs between x = 1 and x = 4 resulted in compounds with increasing Sr contents, for which single-crystal diffraction studies revealed the following Sr/(Sr + Ca) atomic ratios: 0.133,0.268, 0.409 and 0.559. They are isostructural to the pure calcium end-member (x = 0) and adopt the orthorhombic space group Pnnm. Evolution of the unit-cell parameters and cell volumes of the solid-solution series are defined by linear or nearly linear trends when plotted against the Sr/(Sr + Ca) atomic ratio. Replacement of calcium with strontium atoms on the different sites shows clear preferences for specific positions. For the experiment with x = 5, formation of bredigite-related single-crystals with Sr/(Sr + Ca) = 0.675 was observed. These samples, however, exhibited a halved c lattice parameter when compared with the corresponding value in the Pnnm structure, pointing to a compositionally induced phase transition somewhere in region between Sr/(Sr + Ca) = 0.559 and 0.675. The crystal structure of this new phase with composition Ca2.32Sr4.82Mg0.86[SiO4]4 was successfully determined in space group Pbam. Basic crystallographic data are as follows: a = 18.869(2) Å, b = 6.9445(8) Å, c = 5.5426(6) Å, V = 726.28(14) Å3, Z = 2. Structure determination was accomplished using charge flipping. Subsequent least-squares refinements resulted in a residual of R(|F|) = 2.70% for 822 independent reflections and 87 parameters. The Pbam- and the Pnnm-structures are in a group-subgroup relationship and topologically related. Both are based on so-called pinwheel-like MSi6O24 clusters consisting of a central magnesium-dominated [MO6]-octahedron as well as six attached [SiO4]-tetrahedra. The clusters are linked into chain-like elements running along [001]. Linkage between the chains is provided by mixed Sr/Ca positions with 6 to 10 oxygen ligands. Differences between the two phases result from changes in Sr-Ca site occupancies in combination with displacements of the atoms and tilts of the tetrahedra. The distortion pattern has been studied using group-theoretical methods including mode analysis. Notably, for the samples with x = 6 and x = 7—the latter corresponding to the hypothetical pure strontium end-member composition—no bredigite-type phases could be identified, indicating that there is an upper limit for the Sr-uptake.

X-ray Crystal Structure Analysis of Magnetoelectric Metal UNi4B

The crystal structure of the magnetoelectric metal UNi4B was determined from high-resolution synchrotron X-ray diffraction experiments using single-crystalline samples. The direct method and the least-square refinement indicate a structural model with the space group Cmcm (no. 63, \(D_{2h}^{17}\)), where U atoms form a pseudo-triangular lattice in the U–Ni–B layers stacking along the a-axis alternately with the Ni layers. The refined values of the structural parameters including anisotropic atomic displacement parameters are provided for all atoms in the unit cell. The obtained structural model is discussed in terms of the magnetoelectric effect reported for this compound.

Growth, single crystal investigation, hirshfeld surface analysis, DFT studies, molecular docking, physico-chemical characterization and, in vitro, antioxidant activity of a novel hybrid complex

Interaction of the diphosphoric acid (H4P2O7) and organic ligand (3.4-dimethylaniline) with transition metal ions, cobalt (II) chloride leads to the formation of novel stable Co(II)-diphosphate cluster with empirical formula (C8H12N)2[Co(H2P2O7)2(H2O)2].2H2O. The structure of the synthesized material was confirmed by single crystal XRD at 120 ​K. The crystal was plate and crystallized in the triclinic P 1¯ space group with a ​= ​7.5340(4) Å, b ​= ​7.5445(4) Å, c ​= ​13.6896(8) Å, α ​= ​84.215(5)°, β ​= ​76.038(5)°, γ ​= ​74.284(5)°, V ​= ​726.38(7) Å3 and Z ​= ​1. Full-matrix least-squares refinement converged at R ​= ​0.035 and Rw ​= ​0.088 for 3636 independent observed reflections. Indeed, the purity phase was confirmed by the powder X-ray diffraction. A detailed analysis of the intermolecular close interactions and their percentage contribution has been performed based on the Hirshfeld surfaces and their associated two-dimensional fingerprint plots. In this context, spectroscopic studies were performed to distinguish the different chemical functional groups and their environments in this molecule. To determine the optical properties, the UV–Visible and luminescence behavior were investigated. The magnetic properties have been investigated in the temperature range 2–300 k. The geometry of the hybrid complex was optimized in the gas phase, using density functional theory (B3LYP) with the 6-31+G (d,p) basis sets, it is found that the calculated and the experimental results were in good consistency. Furthermore, the synthesized product was screened for its antioxidant activities. Molecular docking study was additionally carried.

LamaGOET: an interface for quantum crystallography.

In quantum crystallography, theoretical calculations and crystallographic refinements are closely intertwined. This means that the employed software must be able to perform both quantum-mechanical calculations and crystallographic least-squares refinements. So far, the program Tonto is the only one able to do that. The lamaGOET interface described herein deals with this issue since it interfaces dedicated quantum-chemical software (the widely used Gaussian package and the specialized ELMOdb program) with the refinement capabilities of Tonto. Three different flavours of quantum-crystallographic refinements of the dipetide glycyl-l-threonine dihydrate are presented to showcase the capabilities of lamaGOET: Hirshfeld atom refinement (HAR), HAR-ELMO, namely HAR coupled with extremely localized molecular orbitals, and X-ray constrained wavefunction fitting.

Fleetite, Cu2RhIrSb2, a New Species of Platinum-Group Mineral from the Miass Placer Zone, Southern Urals, Russia

ABSTRACT Fleetite, Cu2RhIrSb2, a new species of platinum-group mineral (PGM), was discovered intergrown with an Os–Ir–Ru alloy in the Miass Placer Zone (Au–PGE), southern Urals, Russia. A single grain 50 μm across was found. Osmium, ruthenium, and iridium are the main associated minerals; also present are Pt–Fe alloys, laurite, Sb-rich irarsite, Rh-rich tolovkite, kashinite, anduoite, ferronickelplatinum, heazlewoodite, PGE-bearing pentlandite and digenite, as well as micrometric inclusions of forsterite (Fo93.7), chromite–magnesiochromite, and Mg-rich edenite. In reflected light, fleetite is light gray; it is opaque, isotropic, non-pleochroic, and non-bireflectant. We report reflectance values measured in air. A mean of seven point-analyses (wavelength-dispersive spectrometry) gave Cu 13.93, Ni 8.60, Fe 0.10, Ir 28.07, Rh 7.91, Ru 1.96, Sb 39.28, total 99.85 wt.%, corresponding to (Cu1.41Ni0.58Fe0.01)Σ2.00(Rh0.49Ni0.36Ru0.12)Σ0.97Ir0.95Sb2.08 on the basis of six atoms per formula unit, taking into account the structural results. The calculated density is 10.83 g/cm3. Single-crystal X-ray studies show that fleetite is cubic, space group Fdm (#227), a = 11.6682(8) Å, V = 1588.59(19) Å3, and Z = 16. A least-squares refinement of X-ray powder-diffraction data gave a = 11.6575(5) Å and V = 1584.22(19) Å3. The strongest five reflections in the powder pattern [d in Å(I)(hkl)] are: 6.70(75)(111), 4.13(100)(220), 3.52(30)(311), 2.380(50)(422), 2.064(40)(440). Results of synchrotron micro-Laue diffraction experiments are consistent [a = 11.66(2) Å]. The crystal structure of fleetite was solved and refined to R = 0.0340 based upon 153 reflections with Fo > 4σ(Fo). It is isotypic with Pd11Bi2Se2 and best described as intermetallic, with all metal atoms in 12-fold coordination. Fleetite and other late exotic phases were formed by reaction of the associated alloy phases with a fluid phase enriched in Sb, As, and S in circulation in the cooling ophiolite source-rock. The mineral is named after Michael E. Fleet (1938–2017) in recognition of his significant contributions to the Earth Sciences.

On modelling disordered crystal structures through restraints from molecule-in-cluster computations, and distinguishing static and dynamic disorder.

Distinguishing disorder into static and dynamic based on multi-temperature X-ray or neutron diffraction experiments is the current state of the art, but is only descriptive, not predictive. Here, several disordered structures are revisited from the Cambridge Crystallographic Data Center 'drug subset', the Cambridge Structural Database and own earlier work, where experimental intensities of Bragg diffraction data were available. Using the molecule-in-cluster approach, structures with distinguishable conformations were optimized separately, as extracted from available or generated disorder models of the respective disordered crystal structures. Re-combining these 'archetype structures' by restraining positional and constraining displacement parameters for conventional least-squares refinement, based on the optimized geometries, then often achieves a superior fit to the experimental diffraction data compared with relying on experimental information alone. It also simplifies and standardizes disorder refinement. Ten example structures were analysed. It is observed that energy differences between separate disorder conformations are usually within a small energy window of RT (T = crystallization temperature). Further computations classify disorder into static or dynamic, using single experiments performed at one single temperature, and this was achieved for propionamide.

Accelerated microwave-assisted synthesis and in situ X-ray scattering of tungsten-substituted vanadium dioxide (V1−xWxO2)

Vanadium dioxide (VO2) has been widely studied due to its metal-insulator phase transition at 68 °C, below which it is a semiconducting monoclinic phase, P21/c, and above it is a metallic tetragonal phase, P42/mnm. Substituting vanadium with transition metals allows transition temperature tunability. An accelerated microwave-assisted synthesis for VO2 and 5d tungsten-substituted VO2 presented herein decreased synthesis time by three orders of magnitude while maintaining phase purity, particle size, and transition character. Tungsten substitution amount was determined using inductively coupled plasma-optical emission spectroscopy. Differential scanning calorimetry, superconducting quantum interference device measurements, and in situ heating and cooling experiments monitored through synchrotron X-ray diffraction (XRD) confirmed the transition temperature decreased with increased tungsten substitution. Scanning electron microscopy analyzed through the line-intercept method produced an average particle size of 3–5 μm. Average structure and local structure phase purity was determined through the Rietveld analysis of synchrotron XRD and the least-squares refinement of pair distribution function data.

SFCA-II type Ca2.46Fe3+8.57 Fe2+0.52Al5.45O24 \u2013 an improved structural model for an iron-ore sinter phase

Single crystals of SFCA-II with composition Ca2.46Fe3+8.57Fe2+0.52Al5.45O24 have been obtained from synthesis experiments in the temperature range between 1300 and 1200 °C. Diffraction experiments at ambient conditions yielded the following basic crystallographic data: space group P overline{1} , a = 10.3016(4) Å, b = 10.4656(4) Å, c = 17.9553(6) Å, α = 90.062(3), β = 89.977(3)°, γ = 109.510(3)°, V = 1824.66(12) Å3, Z = 4. Structure determination and subsequent least-squares refinements resulted in a residual of R(|F|) = 0.0349 for 7406 independent reflections and 773 parameters. Site occupancy refinements on the 35 octahedral (M) and tetrahedral (T) positions in the asymmetric unit were aided by crystallochemical considerations and the assumption of charge balance between the cations and anions. The derived formula compares well with the outcome of electron microprobe studies. The crystal structure of SFCA-II shows the typical features of the SFCA-family. It can be built from an alternating sequence of two different types of fundamental layers. For SFCA-II, they are oriented parallel to (100). Layer-type I is solely based on [MO6]-octahedra (M: Ca, Fe3+, Al) forming individual five polyhedra wide bands. Within a single band, the octahedra share common edges. Layer-type II, on the other hand, contains [MO6]-octahedra as well as [TO4]-tetrahedra (T: Al, Fe3+, Fe2+). By corner sharing each [MO6]-group is linked to two adjacent tetrahedra into [MT2O12]-clusters or “winged octahedra”. Linkage between neighboring strips of these moieties is provided by additional [TO4]-tetrahedra arranged in vierer single-chains. Our investigation rectifies previous studies on SFCA-II where wrong atomic coordinates have been published.