3,4-Lutidinium salts with the diiodidoaurate(I) anion: structure of [(3,4-lut)2H]+·[AuI2]−and of two polymorphs of [(3,4-lut)2H+]2·[AuI2]−·I−

2018 ◽  
Vol 74 (3) ◽  
pp. 289-294
Author(s):  
Cindy Döring ◽  
Zhihong Sui ◽  
Peter G. Jones
Keyword(s):  
General Position ◽  
Space Groups ◽  
Layer Structures ◽  
Different Types ◽  
Stacking Patterns

Reactions between potassium tetraiodidoaurate(III) and pyridine (py, C5H5N) or 3,4-lutidine (3,4-dimethylpyridine, 3,4-lut, C7H9N) were tested as possible sources of azaaromatic complexes of gold(III) iodide, but all identifiable products contained gold(I). The previously known structure dipyridinegold(I) diiodidoaurate(I), [Au(py)2]+·[AuI2]−, (3) [Adamset al.(1982).Z. Anorg. Allg. Chem.485, 81–91], was redetermined at 100 K. The reactions with 3,4-lutidine gave three different types of crystal in small quantities. 3,4-Dimethylpyridine–3,4-dimethylpyridinium diiodidoaurate(I), [(3,4-lut)2H]+·[AuI2]−, (1), consists of an [AuI2]−anion on a general position and two [(3,4-lut)2H]+cations across twofold axes. Bis(3,4-dimethylpyridine–3,4-dimethylpyridinium) diiodidoaurate(I) iodide, [(3,4-lut)2H+]2·[AuI2]−·I−, (2), crystallizes as two polymorphs, each forming pseudosymmetric inversion twins, in the space groupsP21andPc(but resemblingP21/mandP2/c), respectively. These are essentially identical layer structures differing only in their stacking patterns and thus might be regarded as polytypes.

Frequency distribution of space groups in soluble and membrane proteins and their complexes

2021 ◽  
Vol 77 (6) ◽  
pp. 187-191
Author(s):  
Rajneesh K. Gaur
Keyword(s):  
Membrane Proteins ◽  
Frequency Distribution ◽  
Data Bank ◽  
Frequency Distributions ◽  
Space Group ◽  
Space Groups ◽  
Group Frequency ◽  
Different Types ◽  
Analytical Assessment ◽  
Three Space

The space-group frequency distributions for two types of proteins and their complexes are explored. Based on the incremental availability of data in the Protein Data Bank, an analytical assessment shows a preferential distribution of three space groups, i.e. P212121 > P1211 > C121, in soluble and membrane proteins as well as in their complexes. In membrane proteins, the order of the three space groups is P212121 > C121 > P1211. The distribution of these space groups also shows the same pattern whether a protein crystallizes with a monomer or an oligomer in the asymmetric unit. The results also indicate that the sizes of the two entities in the structures of soluble proteins crystallized as complexes do not influence the frequency distribution of space groups. In general, it can be concluded that the space-group frequency distribution is homogenous across different types of proteins and their complexes.

2. Symmetry

2016 ◽  
pp. 24-38
Author(s):  
A. M. Glazer
Keyword(s):  
Crystal Structure ◽  
Reflection Point ◽  
Notation System ◽  
Space Group ◽  
Space Groups ◽  
Different Types ◽  
Point Groups

In order to explain what crystals are and how their structures are described, we need to understand the role of symmetry, for this lies at the heart of crystallography. ‘Symmetry’ explains the different types of symmetry: rotational, mirror or reflection, point, chiral, and translation. There are thirty-two point groups and seven crystal systems, according to which symmetries are present. These are triclinic, monoclinic, orthorhombic, tetragonal, trigonal, hexagonal, and cubic. Miller indices, lattices, crystal structure, and space groups are described in more detail. Any normal crystal belongs to one of the 230 space group types. Crystallographers generally use the International Notation system to denote these space groups.

Classification of stacking faults and their stepwise elimination during the disorder → order transformation of nickel hydroxide

2006 ◽  
Vol 62 (4) ◽  
pp. 530-536 ◽  
Author(s):  
T. N. Ramesh ◽  
P. Vishnu Kamath ◽  
C. Shivakumara
Keyword(s):  
Diffraction Pattern ◽  
Powder Diffraction ◽  
Nickel Hydroxide ◽  
Stacking Faults ◽  
X Ray ◽  
Local Structures ◽  
Different Types ◽  
Different Temperatures ◽  
Stacking Patterns

Nickel hydroxide samples obtained by strong alkali precipitation are replete with stacking faults. The local structures of the stacking faults resemble the stacking patterns of different polytypic modifications that are theoretically possible among the layered hydroxides. This resemblance becomes a basis for the classification of stacking faults into different types. Each type of stacking fault produces a characteristic non-uniform broadening of peaks in the X-ray powder diffraction pattern of nickel hydroxide. DIFFaX simulations aid the classification and quantification of stacking faults. Hydrothermal treatment of a poorly ordered nickel hydroxide slurry at different temperatures (338–473 K) and different durations (5–48 h) shows that the stacking faults are removed in a stepwise manner. The as-precipitated sample has 17–20% stacking faults of the 3R 2 variety, which evolve into the 2H 2 type at 413 K. The 2H 2 stacking faults persist up to 443 K. The stacking faults are completely removed only at 473 K. At this temperature an ordered β-Ni(OH)2 phase is observed.

Isomers of Diformyl[2.2]paracyclophane; X-Ray Structure Determinations of the Pseudo-ortho Isomer and Two Polymorphs of the Pseudo-meta Isomer

2011 ◽  
Vol 66 (7) ◽  
pp. 705-710
Author(s):  
Peter G. Jones ◽  
Ina Dix ◽  
Mihaela Negru ◽  
Dieter Schollmeyer
Keyword(s):  
General Position ◽  
The Other ◽  
Independent Molecule ◽  
Space Group ◽  
X Ray ◽  
Ortho Isomer ◽  
Layer Structures ◽  
Structure Determinations ◽  
Independent Molecules ◽  
Meta Isomer

Pseudo-ortho- or 4,16-diformyl[2.2]paracyclophane (1) and two polymorphs of pseudo-meta- or 4,13-diformyl[2.2]paracyclophane (2) all display the usual features of [2.2]paracyclophane strain (lengthened C-C bonds and widened C-C(sp3)-C angles in the bridges, narrower sp2 ring angles at the bridgehead atoms, and flattened boat conformations of the rings). All bulk samples were racemates. Polymorph 2a crystallizes in space group P21/n with one molecule in a general position, whereas 2b crystallizes in space group C2 with two independent molecules, each with crystallographic twofold symmetry. All three molecules of 2 are different rotamers with respect to the formyl groups; in 2a one is endo and one exo to the neighbouring bridge, whereas in 2b both formyls are exo in one molecule and endo in the other. In all compounds, the packing patterns are preponderantly associated with C-H・ ・ ・O contacts. In 1 the molecules are connected to form tubes parallel to the short a axis. 2a consists of two interconnected layer structures. One is parallel to (100) and involves chains of molecules parallel to [01̄1]; the other is parallel to (001) and involves chains of molecules parallel to the b axis. 2b consists of two hexagonal layers, one for each independent molecule, parallel to (001). One layer contains bifurcated (C-H・ ・ ・ )2O systems, whereas the single H・ ・ ・O interactions in the other are long and markedly bent.

Orthorhombic sphere packings. V. Trivariant lattice complexes of space groups belonging to crystal class 222

2014 ◽  
Vol 70 (6) ◽  
pp. 591-604 ◽  
Author(s):  
Heidrun Sowa
Keyword(s):  
Sphere Packing ◽  
Tetragonal Symmetry ◽  
Orthorhombic Symmetry ◽  
Sphere Packings ◽  
Homogeneous Sphere ◽  
Space Group ◽  
Space Groups ◽  
Characteristic Space ◽  
Different Types ◽  
Crystal Class

This paper completes the derivation of all types of homogeneous sphere packing with orthorhombic symmetry. The nine orthorhombic trivariant lattice complexes belonging to the space groups of crystal class 222 were examined in regard to the existence of homogeneous sphere packings and of interpenetrating sets of layers of spheres. Altogether, sphere packings of 84 different types have been found; the maximal inherent symmetry is orthorhombic for only 36 of these types. In addition, interpenetrating sets of 63nets occur once. All lattice complexes with orthorhombic characteristic space group give rise to 260 different types of sphere packing in total. The maximal inherent symmetry is orthorhombic for 160 of these types. Sphere packings of 13 types can also be generated with cubic, those of seven types with hexagonal and those of 80 types with tetragonal symmetry. In addition, ten types of interpenetrating sphere packing and two types of sets of interpenetrating sphere layers are obtained. Most of the sphere packings can be subdivided into layer-like subunits perpendicular to one of the orthorhombic main axes.

scholarly journals VRML general position diagrams of non-cubic magnetic space groups

2005 ◽  
Vol 61 (a1) ◽  
pp. c473-c473
Author(s):  
D. B. Litvin ◽  
J. Burke ◽  
N. Cordisco
Keyword(s):  
General Position ◽  
Space Groups

scholarly journals Naturally Layered Aurivillius Phases: Flexible Scaffolds for the Design of Multiferroic Materials

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
J. Halpin ◽  
L. Keeney
Keyword(s):  
Data Storage ◽  
Single Phase ◽  
Driving Forces ◽  
Magnetic Ordering ◽  
Review Article ◽  
Multiferroic Materials ◽  
Aurivillius Phases ◽  
Layer Structures ◽  
Material Systems ◽  
Different Types

The Aurivillius layer-structures, described by the general formula Bi2O2(Am-1BmO3m+1), are naturally 2-dimensionally nanostructured. They are very flexible frameworks for a wide variety of applications, given that different types of cations can beaccommodated both at the A- and B-sites. In this review article, we describe how the Aurivillius phases are a particularly attractive class of oxides for the design of prospective single phase multiferroic systems for multi-state data storage applications, as they offer the potential to include substantial amounts of magnetic cations within a strongly ferroelectric system. The ability to vary m yields differing numbers of symmetrically distinct B-site locations over which the magnetic cations can be distributed and generates driving forces for cation partitioning and magnetic ordering. We discuss how out-of-phase boundary and stacking fault defects can further influence local stoichiometry and the extent of cation partitioning in these intriguing material systems.

Über Wirkungsbereichsteilungen von kubischer Symmetrie II. Die Typen von Wirkungsbereichspolyedern in den symmorphen kubischen Raumgruppen

1981 ◽  
Vol 157 (3-4) ◽  
Author(s):  
Peter Engel
Keyword(s):  
Dimensional Space ◽  
Three Dimensional ◽  
Cubic Symmetry ◽  
Space Groups ◽  
Different Types ◽  
Three Dimensional Space

AbstractPartitions of the three-dimensional space by Dirichlet domains with cubic symmetry have been studied. Within the symmorphic cubic space groups a total of 91 different types of Dirichlet domains were found and their fields of existence were accurately determined. The occurence of the same type of Dirichlet domain in various space groups was investigated. In these space groups the

VRML general position diagrams of magnetic space groups

2006 ◽  
Vol 39 (4) ◽  
pp. 620-620
Author(s):  
J. S. Burke ◽  
N. R. Cordisco ◽  
D. B. Litvin
Keyword(s):  
General Position ◽  
Magnetic Moments ◽  
Three Dimensional ◽  
Space Groups

Three-dimensional general position diagrams of the superfamilies of all non-cubic magnetic space groups have been developed. The diagrams can be rotated and zoomed to aid in the visualization of the general position diagrams and include both the general positions of the atoms and the general orientations of the associated magnetic moments.

X-Ray Studies on Phospholipid Bilayers I. Polymorphic Forms of Dimyristoyl Lecithin

1981 ◽  
Vol 36 (9-10) ◽  
pp. 875-879 ◽  
Author(s):  
M. Suwalsky ◽  
J. Tapia
Keyword(s):  
Relative Humidity ◽  
Phospholipid Bilayers ◽  
Molecular Conformations ◽  
X Ray ◽  
Space Groups ◽  
Cell Dimensions ◽  
Different Types ◽  
Polymorphic Forms ◽  
Diffraction Patterns ◽  
Unit Cell Dimensions

Abstract A structural study of the synthetic phospholipid, L-a-dimyristoyl lecithin (DM L), has been m ade by X-ray fiber diffraction methods. Three different types of oriented specimens were prepared. They were X-ray photographed under the same conditions, including tem perature and relative humidity. T hree different types of diffraction patterns, corresponding to different confor­ mations and/or packing arrangements, were found. They are characterized by their unit cell dimensions, space groups, molecular conformations, and packing arrangements.

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