The compound poly[2-hydroxy-N-methylethan-1-aminium [μ3-cyanido-κ3 C:C:N-di-μ-cyanido-κ4 C:N-dicuprate(I)]], {(C3H10NO)[Cu2(CN)3]} n or [meoenH]Cu2(CN)3, crystallizes in the tetragonal space group P43. The structure consists of a three-dimensional (3D) anionic CuICN network with noncoordinated protonated N-methylethanolamine cations providing charge neutrality. Pairs of cuprophilic Cu atoms are bridged by the C atoms of μ3-cyanide ligands, which link these units into a 43 spiral along the c axis. The spirals are linked together into a 3D anionic network by the two other cyanide groups. The cationic moieties are linked into their own 43 spiral via N—H...O and O—H...O hydrogen bonds, and the cations interact with the 3D network via an unusual pair of N—H...N hydrogen bonds to one of the μ2-cyanide groups. Thermogravimetric analysis indicates an initial loss of the base cation and one cyanide as HCN at temperatures in the range 130–250 °C to form CuCN. We show how loss of a specific cyanide group from the 3D CuCN structure could form the linear CuCN structure. Further heating leaves a residue of elemental copper, isolated as the oxide.
The crystal structures of a new polymorph of dipotassium hydrogen citrate, 2K + ·HC 6 H 5 O 7 2− , and potassium rubidium hydrogen citrate, K + ·Rb + ·HC 6 H 5 O 7 2− , have been solved and refined using laboratory powder X-ray diffraction and optimized using density functional techniques. In the new polymorph of the dipotassium salt, KO 7 and KO 8 coordination polyhedra share corners and edges to form a three-dimensional framework with channels parallel to the a axis and [111]. The hydrophobic methylene groups face each other in the channels. The un-ionized carboxylic acid group forms a strong charge-assisted hydrogen bond to the central ionized carboxylate group. The hydroxy group forms an intermolecular hydrogen bond to a different central carboxylate group. In the potassium rubidium salt, the K + and Rb + cations are disordered over two sites, in approximately 0.72:0.28 and 0.28:0.72 ratios. KO 8 and RbO 9 coordination polyhedra share corners and edges to form a three-dimensional framework with channels parallel to the a axis. The un-ionized carboxylic acid group forms a strong charge-assisted hydrogen bond to an ionized carboxylate group. The hydroxy group forms an intermolecular hydrogen bond to the central carboxylate group. Density functional theory (DFT) calculations on the ordered cation structures suggest that interchange of K + and Rb + at the two cation sites changes the energy insignificantly.
Structural characterization of the ionic title complex, [MgBr(THF)5][Co(dpbz)2]·2THF [THF is tetrahydrofuran, C4H8O; dpbz is 1,2-bis(diphenylphosphanyl)benzene, C30H24P2], revealed a well-separated cation and anion co-crystallized with two THF solvent molecules that interact with the cation via weak C—H⋯O contacts. The geometry about the cobalt center is pseudotetrahedral, as is expected for a d10 metal center, only deviating from an ideal tetrahedral geometry because of the restrictive bite angles of the bidentate phosphane ligands. Three THF ligands of the cation and one co-crystallized THF solvent molecule are each disordered over two orientations. In the extended structure, the cations and THF solvent molecules are arranged in (100) sheets that alternate with layers of anions, the latter of which show various π-interactions, which may explain the particular packing arrangement.
The LaCoxMn1-xO3 perovskite series has been widley studied as responses to chemical composition or volume give rise to a variety of electrical and magnetic properties [1]. Volume changes can be induced by the application of pressure, which can be used to study structural-property relationships. High-pressure neutron-diffraction experiments have been performed on LaCo0.9Mn0.1O3 and LaCoO3 powders. Neutron powder diffraction is essential to determine the structure of perovskite-like oxides. The high-pressure structural evolution of LaCo0.9Mn0.1O3 will be presented [2]. The change in tilting angle and strain has been determined upon pressure. This study compliments high-pressure magnetisation measurements, where the Curie temperature shows a strong dependence on applied pressure. A structural study of LaCoO3 as a function of pressure and temperature using neutron diffraction will also be presented [3]. This study is of great interest for its unique temperature-dependent electronic properties. Tha aformentioned experiments have been carried out on the PEARL instrument, the highpressure-dedicated diffractometer at ISIS, STFC [4]. We are developing new pressure cells for neutron diffraction to extend the maximum achievable pressure at ISIS.
A characterization of the Cu Kα1,2 spectrum is presented, including the 2p satellite line, Kα3,4, the details of which are robust enough to be transferable to other experiments. This is a step in the renewed attempts to resolve inconsistencies in characteristic X-ray spectra between theory, experiment and alternative experimental geometries. The spectrum was measured using a rotating anode, monolithic Si channel-cut double-crystal monochromator and backgammon detector. Three alternative approaches fitted five Voigt profiles to the data: a residual analysis approach; a peak-by-peak fit; and a simultaneous constrained method. The robustness of the fit is displayed across three spectra obtained with different instrumental broadening. Spectra were not well fitted by transfer of any of three prior characterizations from the literature. Integrated intensities, line widths and centroids are compared with previous empirical fits. The novel experimental setup provides insight into the portability of spectral characterizations of X-ray spectra. From the parameterization, an estimated 3d shake probability of 18% and a 2p shake probability of 0.5% are reported.
Graphene, monoatomic layer of graphite, with its unique properties has created a revolution in materials chemistry on the nanoscale in the 21st century.Graphene or its most commonly produced form, reduced graphene oxide (rGO) based nanocomposites, particularly those with metal oxides has added a new dimension in this craze with their buoyant performance in various critical area of our interest, particularly in environmental pollution and energy storage crisis [1].rGO/MnOx and rGO/SnOy binary nanocomposites with their low cost, easy synthesis and environmental benignity, constitute some of the ideal examples in this regard [2][3].Consequently, the rGO based ternary nanocomposites of these metal oxides deserves attention for synthesis and analysis to judge their suitability in the aforementioned fields.However, unlike many others, there have been no report so far in this regard.In our present work, we have synthesized rGO/MnOx/SnOy ternary nanocomposite in a three-step method.According to FTIR, XRD and FESEM analysis, the nanocomposite consist of cubic MnO and tetragonal Mn3O4 and SnO2 adorned on reduced graphene oxide sheet.Organic pollutant removal behavior of the nanocomposite was studied at 30°C with methylene blue as a model dye solution by visible spectroscopy analysis.The ternary nanocomposite showed maximum adsorption capacity at acidic pH and at pH=3 it was 17.7 mg/g and it was found to be more effective at its lower dosage.The electrochemical energy storage performance was evaluated in a threeelectrode system in 0.5 M Na2SO4 solution.Cyclic voltammetry and chronopotentiometry of the ternary nanocomposite showed that, within 0-1 V, at 0.5 A/g, it has a specific capacitance of 145.6 F/g.In cyclic stability study, the nanocomposite required almost same charging time compared to its discharging time and retained 84% capacitance, even after 500 cycles.In impedimetric analysis, the nanocomposite showed very low charge transfer resistance.Thus, the ternary nanocomposite possess a good potential to be used in organic pollutant removal as well as a medium of electrochemical energy storage.
A number of X-ray analyses of an enzyme involved in a key early stage of tetrapyrrole biosynthesis are reported. Two structures of human 5-aminolaevulinate dehydratase (ALAD), native and recombinant, have been determined at 2.8 Å resolution, showing that the enzyme adopts an octameric quaternary structure in accord with previously published analyses of the enzyme from a range of other species. However, this is in contrast to the finding that a disease-related F12L mutant of the human enzyme uniquely forms hexamers [Breinig et al. (2003), Nature Struct. Biol. 10, 757-763]. Monomers of all ALADs adopt the TIM-barrel fold; the subunit conformation that assembles into the octamer includes the N-terminal tail of one monomer curled around the (α/β)8 barrel of a neighbouring monomer. Both crystal forms of the human enzyme possess two monomers per asymmetric unit, termed A and B. In the native enzyme there are a number of distinct structural differences between the A and B monomers, with the latter exhibiting greater disorder in a number of loop regions and in the active site. In contrast, the second monomer of the recombinant enzyme appears to be better defined and the active site of both monomers clearly possesses a zinc ion which is bound by three conserved cysteine residues. In native human ALAD, the A monomer also has a ligand resembling the substrate ALA which is covalently bound by a Schiff base to one of the active-site lysines (Lys252) and is held in place by an ordered active-site loop. In contrast, these features of the active-site structure are disordered or absent in the B subunit of the native human enzyme. The octameric structure of the zinc-dependent ALAD from the hyperthermophile Pyrobaculum calidifontis is also reported at a somewhat lower resolution of 3.5 Å. Finally, the details are presented of a high-resolution structure of the Escherichia coli ALAD enzyme co-crystallized with a noncovalently bound moiety of the product, porphobilinogen (PBG). This structure reveals that the pyrrole side-chain amino group is datively bound to the active-site zinc ion and that the PBG carboxylates interact with the enzyme via hydrogen bonds and salt bridges with invariant residues. A number of hydrogen-bond interactions that were previously observed in the structure of yeast ALAD with a cyclic intermediate resembling the product PBG appear to be weaker in the new structure, suggesting that these interactions are only optimal in the transition state.
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No deterministic approach to obtaining a crystal structure from a set of diffraction intensities exists, despite significant progress in traditional probabilistic direct methods. One of the biggest hurdles in determining a crystal structure algebraically is solving a system of many polynomial equations of high power on intensities in terms of atomic coordinates. In this study, homotopy continuation is used for exhaustive investigation of such systems and an optimized homotopy continuation method is developed with random restarts to determine small (N < 5) crystal structures from a minimum set of error-free intensities.
An experimental determination of the magnetic pair distribution function (mPDF) defined in an earlier paper [Frandsen et al. (2014). Acta Cryst. A70, 3-11] is presented for the first time. The mPDF was determined from neutron powder diffraction data from a reactor and a neutron time-of-flight total scattering source on a powder sample of the antiferromagnetic oxide MnO. A description of the data treatment that allowed the measured mPDF to be extracted and then modelled is provided and utilized to investigate the low-temperature structure of MnO. Atomic and magnetic co-refinements support the scenario of a locally monoclinic ground-state atomic structure, despite the average structure being rhombohedral, with the mPDF analysis successfully recovering the known antiferromagnetic spin configuration. The total scattering data suggest a preference for the spin axis to lie along the pseudocubic [10{\overline 1}] direction. Finally, r-dependent PDF refinements indicate that the local monoclinic structure tends toward the average rhombohedral R{\overline 3}m symmetry over a length scale of approximately 100 Å.
The occurrence frequency of the {110} twin in aragonite is explained by the existence of an important substructure (60% of the atoms) which crosses the composition surface with only minor perturbation (about 0.2 Å) and constitutes a common atomic network facilitating the formation of the twin. The existence of such a common substructure is shown by the C2/c pseudo-eigensymmetry of the crystallographic orbits, which contains restoration operations whose linear part coincides with the twin operation. Furthermore, the local analysis of the composition surface in the aragonite structure shows that the structure is built from slices which are fixed by the twin operation, confirming and reinforcing the crystallographic orbit analysis of the structural continuity across the composition surface.
The implications of the paper by Grimmer [Acta Cryst.(2015), A71, 143–149] are discussed.
Neither International Tables for Crystallography (ITC) nor available crystallography textbooks state explicitly which of the 14 Bravais types of lattices are special cases of others, although ITC contains the information necessary to derive the result in two ways, considering either the symmetry or metric properties of the lattices. The first approach is presented here for the first time, the second has been given by Michael Klemm in 1982. Metric relations between conventional bases of special and general lattice types are tabulated and applied to continuous equi-translation phase transitions.
Accurate structure refinement from electron-diffraction data is not possible without taking the dynamical-diffraction effects into account. A complete three-dimensional model of the structure can be obtained only from a sufficiently complete three-dimensional data set. In this work a method is presented for crystal structure refinement from the data obtained by electron diffraction tomography, possibly combined with precession electron diffraction. The principle of the method is identical to that used in X-ray crystallography: data are collected in a series of small tilt steps around a rotation axis, then intensities are integrated and the structure is optimized by least-squares refinement against the integrated intensities. In the dynamical theory of diffraction, the reflection intensities exhibit a complicated relationship to the orientation and thickness of the crystal as well as to structure factors of other reflections. This complication requires the introduction of several special parameters in the procedure. The method was implemented in the freely available crystallographic computing system Jana2006.
The affine and Euclidean normalizers of the subperiodic groups, the frieze groups, the rod groups and the layer groups, are derived and listed. For the layer groups, the special metrics used for plane-group Euclidean normalizers have been considered.
One of the main goals in the study of color symmetry is to classify colorings of symmetrical objects through their color groups. The term color group is taken to mean the subgroup of the symmetry group of the uncolored symmetrical object which induces a permutation of colors in the coloring. This work looks for methods of determining the color group of a colored symmetric object. It begins with an index n subgroup H of the symmetry group G of the uncolored object. It then considers H-invariant colorings of the object, so that the color group H(*) will be a subgroup of G containing H. In other words, H ≤ H(*) ≤ G. It proceeds to give necessary and sufficient conditions for the equality of H(*) and G. If H(*) ≠ G and n is prime, then H(*) = H. On the other hand, if H(*) ≠ G and n is not prime, methods are discussed to determine whether H(*) is G, H or some intermediate subgroup between H and G.
This work investigates symmetry and color symmetry properties of Kepler, Heesch and Laves tilings embedded on a flat torus and their geometric realizations as tilings on a round torus in Euclidean 3-space. The symmetry group of the tiling on the round torus is determined by analyzing relevant symmetries of the planar tiling that are transformed to axial symmetries of the three-dimensional tiling. The focus on studying tilings on a round torus is motivated by applications in the geometric modeling of nanotori and the determination of their symmetry groups.
A detailed set of synthetic and crystallographic guidelines for the crystalline sponge method based upon the analysis of expediently synthesized crystal sponges using third-generation synchrotron radiation are reported. The procedure for the synthesis of the zinc-based metal-organic framework used in initial crystal sponge reports has been modified to yield competent crystals in 3 days instead of 2 weeks. These crystal sponges were tested on some small molecules, with two being unexpectedly difficult cases for analysis with in-house diffractometers in regard to data quality and proper space-group determination. These issues were easily resolved by the use of synchrotron radiation using data-collection times of less than an hour. One of these guests induced a single-crystal-to-single-crystal transformation to create a larger unit cell with over 500 non-H atoms in the asymmetric unit. This led to a non-trivial refinement scenario that afforded the best Flack x absolute stereochemical determination parameter to date for these systems. The structures did not require the use of PLATON/SQUEEZE or other solvent-masking programs, and are the highest-quality crystalline sponge systems reported to date where the results are strongly supported by the data. A set of guidelines for the entire crystallographic process were developed through these studies. In particular, the refinement guidelines include strategies to refine the host framework, locate guests and determine occupancies, discussion of the proper use of geometric and anisotropic displacement parameter restraints and constraints, and whether to perform solvent squeezing/masking. The single-crystal-to-single-crystal transformation process for the crystal sponges is also discussed. The presented general guidelines will be invaluable for researchers interested in using the crystalline sponge method at in-house diffraction or synchrotron facilities, will facilitate the collection and analysis of reliable high-quality data, and will allow construction of chemically and physically sensible models for guest structural determination.
Tables of the scanning of two-dimensional space groups are presented to determine the frieze-group symmetry of lines that transect two-dimensional crystals. It is shown how these tables can be used to predict the (001) projection symmetries of migration-related segments of coincidence site lattice tilt boundaries with [001] tilt axis.
Resumen del poster presentado al 29th European Crystallographic Meeting, celebrado en Rovinj (Croacia) del 23 al 28 de agosto de 2015.
