scholarly journals Entanglement of Square Nets in Covalent Organic Frameworks

2021 ◽  
Author(s):  
Fangying Jin ◽  
Lac Ha Nguyen ◽  
Zhiye Zhong ◽  
Xing Han ◽  
Chenhui Zhu ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Single Crystal ◽  
Design Principles ◽  
Covalent Organic Frameworks ◽  
Building Unit ◽  
Π Stacking ◽  
Diffraction Structure ◽  
Crystal Electron

Two entangled 2D square COFs have been synthesized from 4,4',4'',4'''-(9,9'-spirobi[fluorene]-2,2',7,7'-tetrayl)-tetrabenzaldehhyde (SFTB) and p-phenylenediamine (PPA) and benzidine (BZD) to form COF-38, [(SFTB)(PPA)2]imine and its isoreticular form COF-39, [(SFTB)(BZD)2]imine. We also report the single crystal electron diffraction structure of COF-39 and find that it is composed of mutually entangled 2D square nets (sql). These COFs represent the first examples of entangled 2D COF structures, which as we illustrate were made possible by our strategy of using the distorted tetrahedral SFTB building unit. SFTB overcomes the propencity of 2D COFs to stack through π-π stacking and allows for entanglements to form. This work adds significantly to the design principles of COFs.

Electron crystallography of zeolites. 3. Calcined MCM-22 and MCM-49, a case of subtle differences

2003 ◽  
Vol 218 (9) ◽  
Author(s):  
Douglas L. Dorset
Keyword(s):  
Electron Diffraction ◽  
Single Crystal ◽  
Crystal Structures ◽  
Direct Methods ◽  
Intensity Data ◽  
Electron Crystallography ◽  
Diffraction Intensity ◽  
Crystal Electron

AbstractSingle crystal electron diffraction intensity data, analyzed by direct methods for determining crystallographic phases, have been employed to seek differences between the crystal structures of calcined MCM-22 and MCM-49. A direct comparison of

Compositional variation within some sedimentary chlorites and some comments on their origin

1985 ◽  
Vol 49 (352) ◽  
pp. 375-386 ◽  
Author(s):  
C. D. Curtis ◽  
C. R. Hughes ◽  
J. A. Whiteman ◽  
C. K. Whittle
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Electron Diffraction ◽  
Single Crystal ◽  
Compositional Variation ◽  
Analytical Transmission Electron Microscopy ◽  
Decomposition Reactions ◽  
Transmission Electron ◽  
Diffraction Patterns ◽  
Crystal Electron

AbstractA range of authigenic sedimentary chlorites from sandstones has been studied by analytical transmission electron microscopy. Selected area (single crystal) electron diffraction patterns are of the Ib (β = 90°) polytype confirming the earlier observations of Hayes (1970).TEM analyses show all samples to be relatively rich in both Al and Fe. In the general formula (Mg,Fe,Al)n [Si8−xAlxO20](OH)16, x varies between 1.5 and 2.6; Fe/(Fe + Mg) between 0.47 and 0.83 and n between 10.80 and 11.54. Octahedral Al is close to 3 in this formulation and Fe2+ predominates over Fe3+. Swelling chlorites have significantly different compositions which are consistent with smectite/chlorite interstratifications.The Ib (β = 90°) polytype appears to be stable under conditions of moderate to deep burial. It replaces berthierine and swelling chlorites formed at lower temperatures. As commonly seen in grain coatings, however, it precipitates from porewater; solutes probably being contributed from several mineral decomposition reactions.

Electron-optical data for crystals of scarbroite

1960 ◽  
Vol 32 (248) ◽  
pp. 363-365 ◽  
Author(s):  
G. W. Brindley ◽  
J. J. Comer
Keyword(s):  
Electron Diffraction ◽  
Single Crystal ◽  
Electron Micrographs ◽  
Optical Data ◽  
Diffraction Patterns ◽  
Crystal Electron

SummaryElectron micrographs of scarbroite show thin platy crystals of about 1 μ size, having rhombic outlines with angles 66° ± 1° and 113° ± 1°. Single-crystal electron-diffraction patterns show rectangular net patterns, with d100 = 9·90 Å., d010 = 14·67 Å., γ* = 90° ± 0·05°. Strong hk0 reflections show a pseudohexagonal arrangement, but true symmetry is probably orthorhombic or monoclinic. Faces outlining rhombic forms are of type {11l}, .

Research on the Size Distribution of Intragranular and Boundary Carbides of T91 Steel after Creep

2014 ◽  
Vol 941-944 ◽  
pp. 198-205
Author(s):  
Qiang Wan ◽  
L. Chen ◽  
C. Luo ◽  
Z.G. Li ◽  
Y.M Chen ◽  
...  
Keyword(s):  
High Temperature ◽  
Electron Diffraction ◽  
Single Crystal ◽  
Phase Structure ◽  
Prior Austenite ◽  
Boltzmann Distribution ◽  
Quantitative Metallography ◽  
Precipitated Phase ◽  
Average Size ◽  
Crystal Electron

The high temperature crept tests of T91 steel have been conducted under two different stresses and temperatures. The single crystal electron diffraction is used to identify the precipitated phase structure. The quantity and size of carbides located in boundaries and intragranular area have been obtained by quantitative metallography, respectively. The results showed that the main precipitated carbides in T91 steel are M23C6(M=Fe,Cr) and V4C3,which is located in the grain and at the boundary of prior austenite respectively. In comparison with the carbides at boundary, the average size of intragranular carbides was smaller while the quantity is higher. The distribution of the carbides size crept with different stresses and temperatures is in accordance with a typical Boltzmann distribution.

Ab initio structure determination of interlayer expanded zeolites by single crystal rotation electron diffraction

2014 ◽  
Vol 43 (27) ◽  
pp. 10593-10601 ◽  
Author(s):  
Peng Guo ◽  
Leifeng Liu ◽  
Yifeng Yun ◽  
Jie Su ◽  
Wei Wan ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Single Crystal ◽  
Ab Initio ◽  
Diffraction Data ◽  
Structure Determination ◽  
Electron Diffraction Data ◽  
Crystal Rotation ◽  
Ab Initio Structure ◽  
Crystal Electron

Rotation electron diffraction (RED) combines the beam tilt and goniometer tilt to obtain single crystal electron diffraction data, which has been used forab initiostructure determination of interlayer expanded zeolites.

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