scholarly journals Polytypism of Compounds with the General Formula Cs{Al2[TP6O20]} (T = B, Al): OD (Order-Disorder) Description, Topological Features, and DFT-Calculations

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 708
Author(s):  
Sergey M. Aksenov ◽  
Alexey N. Kuznetsov ◽  
Andrey A. Antonov ◽  
Natalia A. Yamnova ◽  
Sergey V. Krivovichev ◽  
...  
Keyword(s):  
General Formula ◽  
Dft Calculation ◽  
Screw Axis ◽  
Multilayered Structures ◽  
Disordered Structures ◽  
Topological Features ◽  
Type Layer ◽  
Axis Parallel ◽  
Symmetry Operators ◽  
Display Order

The crystal structures of compounds with the general formula Cs{[6]Al2[[4]TP6O20]} (where T = Al, B) display order−disorder (OD) character and can be described using the same OD groupoid family. Their structures are built up by two kinds of nonpolar layers, with the layer symmetries Pc(n)2 (L2n+1-type) and Pc(a)m (L2n-type) (category IV). Layers of both types (L2n and L2n+1) alternate along the b direction and have common translation vectors a and c (a ~ 10.0 Å, c ~ 12.0 Å). All ordered polytypes as well as disordered structures can be obtained using the following partial symmetry operators that may be active in the L2n type layer: the 21 screw axis parallel to c [– – 21] or inversion centers and the 21 screw axis parallel to a [21 – –]. Different sequences of operators active in the L2n type layer ([– – 21] screw axes or inversion centers and [21 – –] screw axes) define the formation of multilayered structures with the increased b parameter, which are considered as non-MDO polytypes. The microporous heteropolyhedral MT-frameworks are suitable for the migration of small cations such as Li+, Na+ Ag+. Compounds with the general formula Rb{[6]M3+[[4]T3+P6O20]} (M = Al, Ga; T = Al, Ga) are based on heteropolyhedral MT-frameworks with the same stoichiometry as in Cs{[6]Al2[[4]TP6O20]} (where T = Al, B). It was found that all the frameworks have common natural tilings, which indicate the close relationships of the two families of compounds. The conclusions are supported by the DFT calculation data.

scholarly journals Crystal structure of 2-{[2-methoxy-5-(trifluoromethyl)phenyl]iminomethyl}-4-nitrophenol

2015 ◽  
Vol 71 (7) ◽  
pp. o466-o467 ◽  
Author(s):  
Nevzat Karadayı ◽  
Songül Şahin ◽  
Yavuz Köysal ◽  
Emine Coşkun ◽  
Orhan Büyükgüngör
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Title Compound ◽  
Helical Chain ◽  
Screw Axis ◽  
Imine Group ◽  
Compound C ◽  
Benzene Rings ◽  
Axis Parallel

In the title compound, C15H11F3N2O4, the N=C bond of the central imine group adopts anEconformation. The dihedral angle between two benzene rings is 6.2 (2)°. There is an intramolecular bifurcated O—H...(N,O) hydrogen bond withS(6) andS(9) ring motifs. In the crystal, molecules are linked by C—H...O hydrogen bonds into a helical chain along the 31screw axis parallel toc. The –CF3group shows rotational disorder over two sites, with occupancies of 0.39 (2) and 0.61 (2).

scholarly journals Crystal structure of (E)-N-(3,4-dimethoxybenzylidene)morpholin-4-amine

2014 ◽  
Vol 70 (9) ◽  
pp. o935-o935 ◽  
Author(s):  
Sevim Türktekin Çelikesir ◽  
Mehmet Akkurt ◽  
Aliasghar Jarrahpour ◽  
Orhan Büyükgüngör
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Least Squares ◽  
Title Compound ◽  
Chair Conformation ◽  
Screw Axis ◽  
Compound C ◽  
Axis Parallel ◽  
Morpholine Ring ◽  
Supramolecular Chains

In the title compound, C13H18N2O3, the benzene ring makes a dihedral angle of 17.19 (11)° with the least-squares plane formed by the four C atoms of the morpholine ring, which adopts a chair conformation. In the crystal, C—H...N hydrogen bonds link the molecules into supramolecular chains running along a 21screw axis parallel to theb-axis direction. Weak C—H...π interactions are also observed.

scholarly journals catena-Poly[[[(acetato-κ2 O,O′)aquacadmium(II)]-μ-L-threoninato-κ3 N,O:O′] monohydrate]

IUCrData ◽  
2018 ◽  
Vol 3 (12) ◽  
Author(s):  
M. Abila Jeba Queen ◽  
K. C. Bright ◽  
S. Mary Delphine
Keyword(s):  
Water Molecule ◽  
Metal Ion ◽  
Lattice Water Molecule ◽  
Cadmium Acetate ◽  
Asymmetric Unit ◽  
Acetate Dihydrate ◽  
Screw Axis ◽  
One Dimensional ◽  
Lattice Water ◽  
Axis Parallel

The title compound, {[Cd(C2H3O2)(C4H8NO3)(H2O)]·H2O} n , was synthesized from the reaction between L-threonine and cadmium acetate dihydrate. The complex consists of the CdII metal ion bonded to bidentate threonine and acetate anions, and one water molecule. The carboxylate group of L-threonine bridges two metal cations related by the crystallographic screw axis parallel to [010], to form a one-dimensional polymeric structure in the crystal. The asymmetric unit is completed by one lattice water molecule, which is involved in hydrogen bonds.

scholarly journals 4,4′-([4,4′-Bipyridine]-1,1′-diium-1,1′-diyl)dibenzoate dihydrate

IUCrData ◽  
2016 ◽  
Vol 1 (6) ◽  
Author(s):  
Mark A. Rodriguez ◽  
Dorina F. Sava Gallis ◽  
James S. Chavez ◽  
Liana M. Klivansky ◽  
Yi Liu
Keyword(s):  
Dihedral Angle ◽  
Water Molecules ◽  
Carboxylate Group ◽  
Screw Axis ◽  
Solvent Water ◽  
Carboxylate Anions ◽  
Benzene Rings ◽  
Axis Parallel ◽  
Pyridinium Cations ◽  
Positively Charged

We report here the synthesis of a neutral viologen derivative, C24H16N2O4·2H2O. The non-solvent portion of the structure (Z-Lig) is a zwitterion, consisting of two positively charged pyridinium cations and two negatively charged carboxylate anions. The carboxylate group is almost coplanar [dihedral angle = 2.04 (11)°] with the benzene ring, whereas the dihedral angle between pyridine and benzene rings is 46.28 (5)°. TheZ-Lig molecule is positioned on a center of inversion (Fig. 1). The presence of the twofold axis perpendicular to thec-glide plane in space groupC2/c generates a screw-axis parallel to thebaxis that is shifted from the origin by 1/4 in theaandcdirections. This screw-axis replicates the molecule (and solvent water molecules) through space. TheZ-Lig molecule links to adjacent moleculesviaO—H...O hydrogen bonds involving solvent water molecules as well as intermolecular C—H...O interactions. There are also π–π interactions between benzene rings on adjacent molecules.

Structural preservation and absolute contrast of catalase crystal sections prepared with tannic acid

1983 ◽  
Vol 41 ◽  
pp. 448-449
Author(s):  
C.W. Akey ◽  
M. Szalay ◽  
S.J. Edelstein
Keyword(s):  
Tannic Acid ◽  
Beef Heart ◽  
X Rays ◽  
Screw Axis ◽  
General Applicability ◽  
Thin Sections ◽  
Beef Liver ◽  
3 Dimensional ◽  
Dimensional Reconstruction ◽  
Structural Preservation

Three methods of obtaining 20 Å resolution in sectioned protein crystals have recently been described. They include tannic acid fixation, low temperature embedding and grid sectioning. To be useful for 3-dimensional reconstruction thin sections must possess suitable resolution, structural fidelity and a known contrast. Tannic acid fixation appears to satisfy the above criteria based on studies of crystals of Pseudomonas cytochrome oxidase, orthorhombic beef liver catalase and beef heart F1-ATPase. In order to develop methods with general applicability, we have concentrated our efforts on a trigonal modification of catalase which routinely demonstrated a resolution of 40 Å. The catalase system is particularly useful since a comparison with the structure recently solved with x-rays will permit evaluation of the accuracy of 3-D reconstructions of sectioned crystals.Initially, we re-evaluated the packing of trigonal catalase crystals studied by Longley. Images of the (001) plane are of particular interest since they give a projection down the 31-screw axis in space group P3121. Images obtained by the method of Longley or by tannic acid fixation are negatively contrasted since control experiments with orthorhombic catalase plates yield negatively stained specimens with conditions used for the larger trigonal crystals.

Imaging of platinum-shadowed macromolecular complexes in dark field

1984 ◽  
Vol 42 ◽  
pp. 146-147
Author(s):  
D.W. Andrews ◽  
F.P. Ottensmeyer
Keyword(s):  
Thin Film ◽  
Three Dimensional ◽  
Average Diameter ◽  
Dark Field ◽  
Bright Field ◽  
Field Mode ◽  
Macromolecular Complexes ◽  
Average Mass ◽  
Topological Features ◽  
Projection Images

Shadowing with heavy metals has been used for many years to enhance the topological features of biological macromolecular complexes. The three dimensional features present in directionaly shadowed specimens often simplifies interpretation of projection images provided by other techniques. One difficulty with the method is the relatively large amount of metal used to achieve sufficient contrast in bright field images. Thick shadow films are undesirable because they decrease resolution due to an increased tendency for microcrystalline aggregates to form, because decoration artefacts become more severe and increased cap thickness makes estimation of dimensions more uncertain.The large increase in contrast provided by the dark field mode of imaging allows the use of shadow replicas with a much lower average mass thickness. To form the images in Fig. 1, latex spheres of 0.087 μ average diameter were unidirectionally shadowed with platinum carbon (Pt-C) and a thin film of carbon was indirectly evaporated on the specimen as a support.

The limits of strain and lattice parameter measurements by CBED

1989 ◽  
Vol 47 ◽  
pp. 518-519
Author(s):  
Hamish L. Fraser
Keyword(s):  
Electron Beam ◽  
Mirror Symmetry ◽  
Local Symmetry ◽  
Lattice Parameter ◽  
Growth Direction ◽  
Surface Relaxation ◽  
Strained Layer ◽  
Axis Parallel ◽  
Local Lattice ◽  
Strained Layer Superlattice

The topic of strain and lattice parameter measurements using CBED is discussed by reference to several examples. In this paper, only one of these examples is referenced because of the limitation of length. In this technique, scattering in the higher order Laue zones is used to determine local lattice parameters. Work (e.g. 1) has concentrated on a model strained-layer superlattice, namely Si/Gex-Si1-x. In bulk samples, the strain is expected to be tetragonal in nature with the unique axis parallel to [100], the growth direction. When CBED patterns are recorded from the alloy epi-layers, the symmetries exhibited by the patterns are not tetragonal, but are in fact distorted from this to lower symmetries. The spatial variation of the distortion close to a strained-layer interface has been assessed. This is most readily noted by consideration of Fig. 1(a-c), which show enlargements of CBED patterns for various locations and compositions of Ge. Thus, Fig. 1(a) was obtained with the electron beam positioned in the center of a 5Ge epilayer and the distortion is consistent with an orthorhombic distortion. When the beam is situated at about 150 nm from the interface, the same part of the CBED pattern is shown in Fig. 1(b); clearly, the symmetry exhibited by the mirror planes in Fig. 1 is broken. Finally, when the electron beam is positioned in the center of a 10Ge epilayer, the CBED pattern yields the result shown in Fig. 1(c). In this case, the break in the mirror symmetry is independent of distance form the heterointerface, as might be expected from the increase in the mismatch between 5 and 10%Ge, i.e. 0.2 to 0.4%, respectively. From computer simulation, Fig.2, the apparent monocline distortion corresponding to the 5Ge epilayer is quantified as a100 = 0.5443 nm, a010 = 0.5429 nm and a001 = 0.5440 nm (all ± 0.0001 nm), and α = β = 90°, γ = 89.96 ± 0.02°. These local symmetry changes are most likely due to surface relaxation phenomena.

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