scholarly journals Air-Stable Dy(III)-Macrocycle Enantiomers: From Chiral to Polar Space Group

CCS Chemistry ◽  
2022 ◽  
pp. 1-24
Author(s):  
Zhenhua Zhu ◽  
Chen Zhao ◽  
Quan Zhou ◽  
Shuting Liu ◽  
Xiao-Lei Li ◽  
...  
Keyword(s):  
Polar Space ◽  
Space Group

A plastically bendable and polar organic crystal

CrystEngComm ◽  
2021 ◽  
Author(s):  
Sotaro Kusumoto ◽  
Akira Sugimoto ◽  
Daisuke Kosumi ◽  
Yang Kim ◽  
Yoshihiro Sekine ◽  
...  
Keyword(s):  
Mechanical Stress ◽  
Polar Space ◽  
Organic Crystal ◽  
Space Group ◽  
High Dielectric

In this communication, an organic crystal of the polar space group Pc that is capable of plastically bending in response to external mechanical stress is reported, and its high dielectric...

Investigation of the Cs x Rb1−x TiOAsO4 Series. II. The Problems of Interpretation of Residual Electron Densities in a Polar Space Group

1998 ◽  
Vol 54 (5) ◽  
pp. 645-651 ◽  
Author(s):  
P. A. Thomas ◽  
M. N. Womersley
Keyword(s):  
Electron Density ◽  
Polar Space ◽  
Worst Case ◽  
Polar Structure ◽  
Space Group ◽  
Disordered Structure ◽  
Strong Inversion ◽  
Residual Electron Density ◽  
Optical Crystal ◽  
True Structure

The problems of refinements of structures in a polar space group, such as Pna21, are illustrated by the example of crystals in the Cs2x Rb2−2x Ti2O2As2O8, caesium rubidium titanyl arsenate, series, which are isostructural with the well known non-linear optical crystal KTiOPO4. It is shown in particular that errors in the data collection and/or refinement tend to contribute positive residual electron density in sites which are related by an inversion operation to the real Cs/Rb sites. This phenomenon is a consequence of the presence of two minima in least-squares space, representing here the possible coordinate sets x,y,z and x,y,−z, for a polar structure and is exacerbated in these structures by the presence of strong inversion psuedo-symmetry. It is shown that in the worst case, the positive residual electron density can be eliminated and an improved agreement to the observed data obtained by refinement of a partially micro-twinned disordered structure in which the Cs/Rb occupancy is split between the main sites and the inversion-related sites. It is argued that the true structure is micro-twinned, including partial occupancy of the additional sites.

Two alkali calcium borates exhibiting second harmonic generation and deep-UV cutoff edges

2019 ◽  
Vol 43 (24) ◽  
pp. 9354-9363
Author(s):  
Peng Ren ◽  
Yun Yang ◽  
Hao Li ◽  
Zhihua Yang ◽  
Shilie Pan
Keyword(s):  
Second Harmonic Generation ◽  
Harmonic Generation ◽  
Second Harmonic ◽  
Polar Space ◽  
Structure Property ◽  
Space Group ◽  
Structure Property Relationships ◽  
Deep Uv

KCa4B3O9 and K0.59Rb0.41Ca4B3O9 crystallize in the polar space group with moderate SHG responses. Calculations were performed to elucidate the structure–property relationships.

scholarly journals From patterns to space groups and the eigensymmetry of crystallographic orbits: a reinterpretation of some symmetry diagrams in IUCr Teaching Pamphlet No. 14

2012 ◽  
Vol 45 (4) ◽  
pp. 834-837
Author(s):  
Leopoldo Suescun ◽  
Massimo Nespolo
Keyword(s):  
Alternative Interpretation ◽  
Polar Space ◽  
Space Group ◽  
Space Groups ◽  
General Orbit

The space group of a crystal pattern is the intersection group of the eigensymmetries of the crystallographic orbits corresponding to the occupied Wyckoff positions. Polar space groups without symmetry elements with glide or screw components smaller than 1/2 do not contain characteristic orbits and cannot be realized in patterns (structures) made by only one crystallographic type of object (atom). The space-group diagram of the general orbit for this type of group has an eigensymmetry that corresponds to a special orbit in a centrosymmetric supergroup of the generating group. This fact is often overlooked, as shown in the proposed solution for Plates (i)–(vi) of IUCr Teaching Pamphlet No. 14, and an alternative interpretation is given.

Chiral and achiral copper(ii) complexes: structure, bonding and biological activities

RSC Advances ◽  
2016 ◽  
Vol 6 (64) ◽  
pp. 59055-59065 ◽  
Author(s):  
Assila Maatar Ben Salah ◽  
Nadhem Sayari ◽  
Houcine Naïli ◽  
Alexander. J. Norquist
Keyword(s):  
Hybrid Materials ◽  
Biological Activities ◽  
Polar Space ◽  
Space Group

A route to noncentrosymmetric hybrid materials is discussed through three noncentrosymmetric materials. These compounds crystallize in either a chiral polar or achiral polar space group, and exhibit high antioxidant and anti-hypertensive activities.

Darstellung und Kristallstruktur von Di-gold(III)bis(selenit)oxid, Au2(SeO3)2O / Preparation and Crystal Structure of Di-gold(III) Bis(selenite) Oxide, Au2(SeO3)2O

1983 ◽  
Vol 38 (1) ◽  
pp. 10-11 ◽  
Author(s):  
Peter G. Jones ◽  
George M. Sheldrick ◽  
Einhard Schwarzmann ◽  
Andreas Vielmäder
Keyword(s):  
Crystal Structure ◽  
Heavy Atom ◽  
Polar Space ◽  
Light Atom ◽  
Space Group ◽  
Extended Structure ◽  
Selenic Acid ◽  
Oxide Ions

Abstract Au2(SeO2)2O was prepared from gold and excess selenic acid in a sealed tube at 533 K. The crystal structure [Pba2, a = 659.2(2), b = 1183.7(3), c = 399.8(1) pm, Z = 2,R = 0.087] was determined; gold atoms are bridged by oxide ions (lying on twofold axes) and selenite ions. The extended structure consists of polymeric layers parallel to the xy-plane. The light atom positions are inaccurate because of the presence of a heavy atom in a polar space group.

Matching selenium-atom peak positions with a different hand or origin

2002 ◽  
Vol 35 (3) ◽  
pp. 368-370 ◽  
Author(s):  
G. David Smith
Keyword(s):  
Computer Program ◽  
Iterative Procedure ◽  
Polar Axis ◽  
Polar Space ◽  
Selenium Atom ◽  
Space Group ◽  
Space Groups ◽  
Fortran 90 ◽  
Symmetry Operations

An algorithm is described for matching and correlating two or more sets of peaks or atoms. The procedure is particularly useful for matching putative selenium atoms from a selenium-atom substructure as obtained fromEmaps from two or more random-atom trials. The algorithm will work for any space group exceptP1. For non-polar space groups, the procedure is relatively straightforward. For polar space groups, the calculation is performed in projection along the polar axis in order to identify potential matching peaks, and an iterative procedure is used to eliminate incorrect peaks and to calculate the displacement along the polar axis. The algorithm has been incorporated into a computer program,NANTMRF, written in Fortran 90. Less than 0.5 s are required to match 27 peaks in space groupP21, and the output lists the correct origin, enantiomorph, symmetry operations, and provides the relative displacements between pairs of matching peaks.

Inorganic structures in space group P31m; coordinate analysis and systematic prediction of new ferroelectrics

2010 ◽  
Vol 66 (2) ◽  
pp. 173-183 ◽  
Author(s):  
S. C. Abrahams
Keyword(s):  
Crystal Structures ◽  
Aluminum Sulfate ◽  
Polar Space ◽  
Candidate Selection ◽  
Primary Sources ◽  
Structural Determination ◽  
Space Group ◽  
Sources Of Uncertainty ◽  
Upper Limit ◽  
Inorganic Crystal

The 62 entries listed in ICSD release 2009/1 under polar space group P31m correspond to 31 families of inorganic crystal structures, some with only one member. Coordinate analysis reveals, over a wide confidence range, 11 of these families as ferroelectric candidates. One includes the well known improper ferroelectric GASH (guanidinium aluminum sulfate hexahydrate), [(C(NH2)3)Al(SO4)2(H2O)6], another the previously predicted ferroelectric CsNO3 phase II. Those remaining include K3Nb3B2O12, the minerals schairerite, galeite and lizardite 1T, LaNi5D6 and γ-CaNi5D6.1, Ca(OCl)2Ca(OH)2, [N(CH3)4]2Mo3S13, Li17Ag3Sn6 and Cs3As5O9. Candidate selection is based upon detecting an approach by the reported atomic arrangement to the symmetry of a corresponding nonpolar supergroup. A further 13 families are typified by their reduced predictive properties, with four others likely to remain polar at higher temperatures and the remaining three noted as having a unit cell larger than reported or a misassigned space group. The primary sources of uncertainty in structurally based predictions of ferroelectricity are the reliability of the underlying structural determination and the upper limit assigned to the cationic displacement magnitudes required to achieve supergroup symmetry.

Basic forms of supramolecular self-assembly organized by parallel and antiparallel hydrogen bonds in the racemic crystal structures of six disubstituted and trisubstituted cyclopentane derivatives

2001 ◽  
Vol 57 (4) ◽  
pp. 539-550 ◽  
Author(s):  
Alajos Kálmán ◽  
Gyula Argay ◽  
László Fábián ◽  
Gábor Bernáth ◽  
Ferenc Fülöp
Keyword(s):  
Hydrogen Bonds ◽  
Self Assembly ◽  
Close Packing ◽  
Polar Space ◽  
Chiral Molecules ◽  
Space Group ◽  
X Ray Crystallography ◽  
Translation Space ◽  
Derivatives Of ◽  
Racemic Crystals

A selection of stereoisomeric 2-hydroxy-1-cyclopentanecarboxamides, a 4-tert-butyl derivative and three tert-butyl derivatives of the respective carboxylic acid were subjected to X-ray crystallography. The optically active molecules (I)–(VI) form racemic crystals. Each racemic structure is basically determined by two intermolecular hydrogen bonds of O—H...O=C—XH and O=C—X—H...OH types (X = O, NH). The partially similar patterns of close packing observed reflect five basic forms of supramolecular self-assembly. In the racemic crystals of chiral molecules, there are homo- and heterochiral chains of molecules formed by the principal (O—H...O=C) hydrogen bonds. These chains assemble either in a parallel or antiparallel mode. The parallel homochiral chains (hop) observed in structure (II), (1R*,2R*)-2-hydroxy-1-cyclopentanecarboxamide, demand the polar space group Pca21, while the parallel heterochiral chains (hep) are organized in antiparallel layers with space group P21/n in structure (VI), (1R*,2S*,5R*-5-tert-butyl-2-hydroxy-1-cyclopentanecarboxylic acid). Heterochiral chains in an antiparallel array (hea) are found in (I), (1R*,2S*)-2-hydroxy-1-cyclopentanecarboxamide, and (V) [(1R*,2S*4S*)-4-tert-butyl-2-hydroxy-1-cyclopentanecarboxylic acid, space group P21/c]. Structures (IV), (1R*,2S*,4R*)-4-tert-butyl-2-hydroxy-1-cyclopentanecarboxylic acid, and (III), (1R*,2R*,4S*)-4-tert-butyl-2-hydroxy-1-cyclopentanecarboxamide, reveal that homochiral chains in an antiparallel array (hoa; cross-linked by heterochiral dimers held together by the second hydrogen bonds) can be formed by either translation (space group P\bar 1) or a screw axis (space group P21/c). These alternatives are denoted hoa1 and hoa2. Similarly, within each pattern (hea, hep and hop) two slightly different alternatives can be expected. The partial similarities in the identified five patterns of hydrogen bonding are described by graph-set notations. Structures (I), (IV) and (V) can be characterized by a common supramolecular synthon, while the highest degree of similarity is shown by the isostructurality of (I) and (V).

Ferroelectric properties and structural refinement of whitlockite-type phosphate Ca8.5Pb0.5Ho(PO4)7

2017 ◽  
Vol 32 (S1) ◽  
pp. S168-S171
Author(s):  
Dina V. Deyneko ◽  
Darya A. Petrova ◽  
Olga N. Leonidova ◽  
Ivan V. Nikiforov ◽  
Bogdan I. Lazoryak
Keyword(s):  
Second Harmonic ◽  
Rietveld Method ◽  
Ferroelectric Properties ◽  
Polar Space ◽  
Structural Refinement ◽  
Space Group ◽  
Cell Parameters ◽  
Oxygen Coordination ◽  
Exact Distributions ◽  
Structural Mechanisms

The system of phosphates Ca9−xPbxHo(PO4)7 were obtained by solid-state reaction and were found to be isotypic with whitlockite-type β-Ca3(PO4)2 (polar space group R3c). The crystal structure encloses five crystallographic sites M1–M5 different in size and oxygen coordination. The unit-cell parameters were determinate using Le Bail decomposition. Rietveld method structural refining showed that Ho3+ ions are located statistically with calcium in M1 and M2 sites, while Pb2+-ions are located in the M3 site. Examination of optical second-harmonic generation evidences non-linear optical activity and confirms polar space group R3c. Structural mechanisms and dielectric features of phase transitions are strongly influenced by the exact distributions of atoms over the crystallographic sites.

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