scholarly journals A chiral uranyl–Kemp’s tricarboxylate cubic framework: structure-directing effect of counterions with three-fold rotational symmetry

2021 ◽  
Author(s):  
Pierre Thuéry ◽  
Jack Harrowfield
Keyword(s):  
Rotational Symmetry ◽  
Framework Structure ◽  
Cubic Symmetry ◽  
Uranyl Cation ◽  
Directing Effect

In the presence of PPh3Me+ cations, Kemp’s tricarboxylate (kta3–) complexes the uranyl cation to give [PPh3Me][UO2(kta)] (1), a triperiodic framework with cubic symmetry and srs topology. The cation is held...

scholarly journals A cubic quasicrystal in a rapidly-solidified Mg-Al alloy

2014 ◽  
Vol 70 (a1) ◽  
pp. C91-C91
Author(s):  
Takeshi Kato ◽  
Takehito Seki ◽  
Eiji Abe
Keyword(s):  
Rotational Symmetry ◽  
Point Group ◽  
Physical Space ◽  
Al Alloy ◽  
Fold Axis ◽  
Cubic Symmetry ◽  
Quasiperiodic Structure ◽  
Diffraction Patterns ◽  
Analysis Of The Images ◽  
Rapidly Solidified

It is commonly accepted that the definition of quasicrystal should include a rotational symmetry forbidden in periodic crystals. On the other hand, the quasicrystal with a conventional point group is theoretically possible [1,2]. In a rapidly-solidified Mg-Al alloy, intriguing electron diffraction patterns (EDPs) were reported, which show a cubic symmetry with aperiodic arrays of Bragg reflections [2]. In the present work, we investigate the detailed structure of the rapidly-solidified Mg-Al phase based on direct structure observations using STEM. In a rapidly-solidified Mg-61 at.% Al alloy, 2-fold, 3-fold, and 4-fold EDPs are obtained (Fig. a), which shows that the structure has the cubic point group. However, the relevant diffraction spots are arranged aperiodically. Especially in the 2-fold EDP, a high density of the spots is observed, and the corresponding HADDF-STEM image shows several remarkable features (Fig. b). Two length scales, L and S, can be definitely observed, and they are arranged quasiperiodically along the 3-fold axis. Their arrangement can be well described by the hyperspace crystallography; a physical space tilted by the angle θ , where tanθ ∼ 1.4, successfully generates the observed quasiperiodic pattern. Simulated EDPs from a simple model without detailed atomic decoration reproduces fairly well the experimental patterns. Further analysis of the images reveals that the present quasiperiodic structure has similar local structure to the stable β-Mg2Al3phase; two lengths correspond to L and S may be reasonably defined. The quasicrystal with a cubic symmetry is unambiguously determined for the first time, based on a direct structural observation. The present results strongly suggest that the noncrystallographic rotational symmetry is not an essential factor to form the quasiperiodic structure, raising a very fundamental, universal question on the physical origin of a long-range order of condensed matters.

scholarly journals 1,1′-{(1E,1′E)-[Octane-1,8-diylbis(azanylylidene)]bis(methanylylidene)}bis(naphthalen-2-ol) in the zwitterionic form

IUCrData ◽  
2017 ◽  
Vol 2 (2) ◽  
Author(s):  
Sabrina Bendia ◽  
Kamel Ouari ◽  
Lydia Karmazin
Keyword(s):  
Solid State ◽  
Hydrogen Bonds ◽  
Title Compound ◽  
Rotational Symmetry ◽  
Three Dimensional ◽  
Framework Structure ◽  
Twofold Axis ◽  
Zwitterionic Form ◽  
Compound C

The title compound, C30H32O2N2, is formed from two units ofortho-hydroxynaphthaldehyde bridged with 1,8-diaminooctane. In the solid state, it exists as a double zwitterion. The N atoms are protonated and the C—O−bonds lengths are 1.265 (2) Å, with intramolecular N—H...O hydrogen bonds formingS(6) ring motifs. The molecule has twofold rotational symmetry, with the twofold axis bisecting the central –CH2—CH2– bond of the bridging octane chain. In the crystal, molecules are linked by N—H...O hydrogen bonds, forming chains propagating along the [-201] direction. The chains are linkedviaC—H...O hydrogen bonds, forming a supramolecular three-dimensional framework structure.

scholarly journals Ethylenediaminium pyridine-2,5-dicarboxylate dihydrate

2006 ◽  
Vol 62 (7) ◽  
pp. o3124-o3126 ◽  
Author(s):  
Graham Smith ◽  
Urs D. Wermuth ◽  
David J. Young ◽  
Peter C. Healy
Keyword(s):  
Hydrogen Bonding ◽  
Title Compound ◽  
Rotational Symmetry ◽  
Three Dimensional ◽  
Water Molecules ◽  
Framework Structure ◽  
Compound C ◽  
Hydrogen Bonding Interactions ◽  
Amine Groups ◽  
Hydrogen Bonded

The title compound, C2H10N2 2+·C7H3NO4 2−·2H2O, forms a three-dimensional hydrogen-bonded framework structure in which both of the amine groups of ethylenediamine are protonated and participate in a total of six hydrogen-bonding interactions with carboxylate O-atom acceptors of the anions as well as the water molecules. The cations lie on crystallographic inversion centres and adopt extended conformations, while the anions have twofold rotational symmetry. This results in the pyridine N atom and its ortho-related CH group being disordered over two 50% occupancy sites.

Comparison of Calculated and Recorded Electron Energy-Loss Spectra of Aluminium and Carbon

1990 ◽  
Vol 48 (2) ◽  
pp. 64-65
Author(s):  
L. Reimer ◽  
R. Oelgeklaus
Keyword(s):  
Fourier Transform ◽  
Energy Loss ◽  
Electron Energy ◽  
Rotational Symmetry ◽  
Mean Free Path ◽  
Single Scattering ◽  
Specimen Thickness ◽  
Two Dimensional ◽  
Image Position ◽  
Electron Energy Loss

Quantitative electron energy-loss spectroscopy (EELS) needs a correction for the limited collection aperture α and a deconvolution of recorded spectra for eliminating the influence of multiple inelastic scattering. Reversely, it is of interest to calculate the influence of multiple scattering on EELS. The distribution f(w,θ,z) of scattered electrons as a function of energy loss w, scattering angle θ and reduced specimen thickness z=t/Λ (Λ=total mean-free-path) can either be recorded by angular-resolved EELS or calculated by a convolution of a normalized single-scattering function ϕ(w,θ). For rotational symmetry in angle (amorphous or polycrystalline specimens) this can be realised by the following sequence of operations :(1)where the two-dimensional distribution in angle is reduced to a one-dimensional function by a projection P, T is a two-dimensional Fourier transform in angle θ and energy loss w and the exponent -1 indicates a deprojection and inverse Fourier transform, respectively.

The need of electron microscopy in the study of domains and domain walls in ferroelectrics

1994 ◽  
Vol 52 ◽  
pp. 550-551
Author(s):  
Wenwu Cao
Keyword(s):  
Domain Wall ◽  
Domain Walls ◽  
High Mobility ◽  
Continuum Theory ◽  
Polarization Vector ◽  
Ferroelectric Materials ◽  
Dielectric Constants ◽  
Nonlocal Coupling ◽  
Cubic Symmetry ◽  
Gradient Energy

Domain structures play a key role in determining the physical properties of ferroelectric materials. The formation of these ferroelectric domains and domain walls are determined by the intrinsic nonlinearity and the nonlocal coupling of the polarization. Analogous to soliton excitations, domain walls can have high mobility when the domain wall energy is high. The domain wall can be describes by a continuum theory owning to the long range nature of the dipole-dipole interactions in ferroelectrics. The simplest form for the Landau energy is the so called ϕ model which can be used to describe a second order phase transition from a cubic prototype,where Pi (i =1, 2, 3) are the components of polarization vector, α's are the linear and nonlinear dielectric constants. In order to take into account the nonlocal coupling, a gradient energy should be included, for cubic symmetry the gradient energy is given by,

Magnetic and magnetoelastic properties of a ferromagnetic single crystal with cubic symmetry

1978 ◽  
Vol 3 ◽  
pp. 479-501 ◽  
Author(s):  
E. Du Trémolet de Lacheisserie ◽  
P. Morin ◽  
J. Rouchy
Keyword(s):  
Single Crystal ◽  
Cubic Symmetry ◽  
Magnetoelastic Properties

Oleanolic Acid Derived from Plants: Synthesis and Pharmacological Properties of A-ring Modified Derivatives

2020 ◽  
Vol 17 (9) ◽  
pp. 1084-1101
Author(s):  
Tingjuan Wu ◽  
Xu Yao ◽  
Guan Wang ◽  
Xiaohe Liu ◽  
Hongfei Chen ◽  
...  
Keyword(s):  
Drug Design ◽  
Oleanolic Acid ◽  
Water Solubility ◽  
Future Application ◽  
The Novel ◽  
Pharmacological Effects ◽  
Framework Structure ◽  
Design And Synthesis ◽  
The Past ◽  
The Relationship

Background: Oleanolic Acid (OA) is a ubiquitous product of triterpenoid compounds. Due to its inexpensive availability, unique bioactivities, pharmacological effects and non-toxic properties, OA has attracted tremendous interest in the field of drug design and synthesis. Furthermore, many OA derivatives have been developed for ameliorating the poor water solubility and bioavailability. Objective: Over the past few decades, various modifications of the OA framework structure have led to the observation of enhancement in bioactivity. Herein, we focused on the synthesis and medicinal performance of OA derivatives modified on A-ring. Moreover, we clarified the relationship between structures and activities of OA derivatives with different functional groups in A-ring. The future application of OA in the field of drug design and development also was discussed and inferred. Conclusion: This review concluded the novel achievements that could add paramount information to the further study of OA-based drugs.

Structure-directing study of 1-methylimidazolium-based dication with tetramethylene as spacer length in the synthesis of microporous silicoaluminophosphates

2021 ◽  
Author(s):  
Thayara Kellen Tavares ◽  
Gabrielli Almeida ◽  
Yuri Variani ◽  
Katia Bernardo-Gusmão ◽  
Paloma Vinaches ◽  
...  
Keyword(s):  
Structure Directing Agent ◽  
Spacer Length ◽  
Organic Structure ◽  
Directing Effect

In this work we study the structure-directing effect of 1-methylimidazolium-based dications with four methylene units as spacer length (4BI), as Organic Structure-Directing Agent (OSDA) in the synthesis of silicoaluminophosphate (SAPO)...

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