[3]Rotane: crystal structure, X-X difference electron density, and phase transition

1991 ◽  
Vol 113 (5) ◽  
pp. 1743-1748 ◽  
Author(s):  
Roland Boese ◽  
Thomas Miebach ◽  
Armin De Meijere
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Electron Density ◽  
Difference Electron Density

Struktur und X-X-Elektronendichteverteilung in Diaminoboranen des Typs (RCH3N)2BCH3 mit R = H, CH3

1991 ◽  
Vol 46 (1) ◽  
pp. 84-96 ◽  
Author(s):  
Norbert Niederprüm ◽  
Roland Boese ◽  
Günter Schmid
Keyword(s):  
Crystal Structure ◽  
Electron Density ◽  
Zone Melting ◽  
Infrared Light ◽  
Monoclinic Space Group ◽  
Difference Electron Density ◽  
Orthorhombic Space Group ◽  
Torsion Angles ◽  
Space Group ◽  
The Mean

Using a miniature zone melting device with focused infrared light it was possible to grow crystals of bis(dimethylamino)methylborane (1) and bis(monomethylamino)methylborane (2) at temperatures o f 182 K and 177 K, respectively. The crystal structure and the X - X difference electron density have been determined at temperatures o f 120 K (1) and 115 K (2).1 crystallizes in the orthorhombic space group Pbca with a = 758.87(7), b = 1559.74(12) and c = 1296.73(12) pm. The mean B - N distance is 143.1(3) pm.2 crystallizes in the monoclinic space group P21/c with a = 775.06(6), b = 1533.94(17), c = 1011.06(10) pm and β = 102.669(7)° with intermolecular N ··· H hydrogen bridges. The mean B - N distance is 141.5(2) pm.It is shown that the variation of torsion angles at small angles has more influence on bond lengths than the same or a greater variation at large angles and that it is necessary to pay more attention to the torsion angles ( C - B - N - C ) rather than to the interplanar angles (plane N ,B,N - plane N ,C,C ).

scholarly journals Differenzelektronendichte im gefalteten 2 π-aromatischen System eines 1,3-Dihydro-1,3-diborets / Difference Electron Density in a Folded 2π-Aromatic System of a 1,3-Dihydro-1,3-diborete

1991 ◽  
Vol 46 (12) ◽  
pp. 1621-1624 ◽  
Author(s):  
Hermann Irngartinger ◽  
Jürgen Hauck ◽  
Walter Siebert ◽  
Manfred Hildenbrand
Keyword(s):  
Crystal Structure ◽  
Density Distribution ◽  
Electron Density ◽  
Electron Density Distribution ◽  
Ring System ◽  
Membered Ring ◽  
Aromatic System ◽  
Difference Electron Density ◽  
Folding Angle

The crystal structure and the X—X difference electron density distribution of 1,3-bis(diisopropylamino)-1,3,dihydro-1,3-diborete (1) has been determined at the temperature of 107 K. Both π-electrons of the folded aromatic four membered ring system (folding angle 47.6°) are uniformly distributed on the four ring bonds with equal lengths (B—C 1.524 A). These bonds are significantly bent.

Structure of and electron density in RbTiOAsO4 at 9.6 K

1999 ◽  
Vol 55 (5) ◽  
pp. 712-720 ◽  
Author(s):  
Jenni Almgren ◽  
Victor A. Streltsov ◽  
Alexander N. Sobolev ◽  
Brian N. Figgis ◽  
Jörgen Albertsson
Keyword(s):  
Phase Transition ◽  
Electron Density ◽  
Room Temperature ◽  
Ferroelectric Properties ◽  
Polarization Vector ◽  
Difference Electron Density ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Structure Factors ◽  
The Difference

Structure factors for rubidium titanyl arsenate, RbTiOAsO4, were measured with Mo Kα radiation (λ = 0.71069 Å) at 9.6 and 295 K. The data show that there is no phase transition between room temperature and 9.6 K. The space group is Pna2 1. Unit-cell parameters are a = 13.218 (1), b = 6.6500 (9) and c = 10.761 (1) Å at 9.6 K, and a = 13.261 (2), b = 6.6791 (8) and c = 10.769 (1) Å at 295 K. As the temperature was lowered from 295 to 9.6 K the Rb atoms moved along the c axis in the direction of the polarization vector, while no significant change was noted for the Ti–O–As network. Strong accumulation and polarization of the difference electron density (Δρ) in exceptionally short covalent Ti—O bonds alternates with the depleted density in long Ti—O bonds. The Δρ near the Ti atoms is polarized and aligned in the negative c direction in accordance with the ferroelectric properties of this material. However, the electron density near the Rb atoms is depleted in this direction and the excess Δρ is moved further away from the nuclei along the c vector.

A study on α-RuCl3 crystal structure by scanning tunneling microscopy

1989 ◽  
Vol 47 ◽  
pp. 30-31
Author(s):  
H.-J. Cantow ◽  
H. Hillebrecht ◽  
S. Magonov ◽  
H. W. Rotter ◽  
G. Thiele
Keyword(s):  
Crystal Structure ◽  
Density Distribution ◽  
Scanning Tunneling Microscopy ◽  
Electron Density ◽  
Structure Determination ◽  
Electron Density Distribution ◽  
Scanning Tunneling ◽  
Monoclinic Space Group ◽  
Tunneling Microscopy ◽  
X Ray

From X-ray analysis, the conclusions are drawn from averaged molecular informations. Thus, limitations are caused when analyzing systems whose symmetry is reduced due to interatomic interactions. In contrast, scanning tunneling microscopy (STM) directly images atomic scale surface electron density distribution, with a resolution up to fractions of Angstrom units. The crucial point is the correlation between the electron density distribution and the localization of individual atoms, which is reasonable in many cases. Thus, the use of STM images for crystal structure determination may be permitted. We tried to apply RuCl3 - a layered material with semiconductive properties - for such STM studies. From the X-ray analysis it has been assumed that α-form of this compound crystallizes in the monoclinic space group C2/m (AICI3 type). The chlorine atoms form an almost undistorted cubic closed package while Ru occupies 2/3 of the octahedral holes in every second layer building up a plane hexagon net (graphite net). Idealizing the arrangement of the chlorines a hexagonal symmetry would be expected. X-ray structure determination of isotypic compounds e.g. IrBr3 leads only to averaged positions of the metal atoms as there exist extended stacking faults of the metal layers.

Dynamic low-dose electron diffraction and imaging of phase transitions in polymers

1993 ◽  
Vol 51 ◽  
pp. 890-891
Author(s):  
David C. Martin ◽  
Jun Liao
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Electron Diffraction ◽  
Low Dose ◽  
Dark Field ◽  
Continuous Change ◽  
Selected Area Electron Diffraction ◽  
Resolution Electron ◽  
Chain Axis ◽  
High Resolution Electron Micrographs

By careful control of the electron beam it is possible to simultaneously induce and observe the phase transformation from monomer to polymer in certain solid-state polymcrizable diacetylenes. The continuous change in the crystal structure from DCHD diacetylene monomer (a=1.76 nm, b=1.36 nm, c=0.455 nm, γ=94 degrees, P2l/c) to polymer (a=1.74 nm, b=1.29 nm, c=0.49 nm, γ=108 degrees, P2l/c) occurs at a characteristic dose (10−4C/cm2) which is five orders of magnitude smaller than the critical end point dose (20 C/cm2). Previously we discussed the progress of this phase transition primarily as observed down the [001] zone (the chain axis direction). Here we report on the associated changes of the dark field (DF) images and selected area electron diffraction (SAED) patterns of the crystals as observed from the side (i.e., in the [hk0] zones).High resolution electron micrographs (HREM), DF images, and SAED patterns were obtained on a JEOL 4000 EX HREM operating at 400 kV.

crystal structure and phase transition in the compound [C6H5CH2NH2CH3]10Sb6Cl28

2006 ◽  
Vol 31 (1) ◽  
pp. 39-48
Author(s):  
Najla Vix-Gurtel ◽  
Chaari Dentzer ◽  
Slaheddine Chaabouni ◽  
Jean-Michel Savariault ◽  
Abdelhamid ben Salah
Keyword(s):  
Crystal Structure ◽  
Phase Transition

Ab-initio investigation of crystal structure and pressure induced phase transition in ThO2 and PuO2

2021 ◽  
pp. 102579
Author(s):  
Shilpa Singh ◽  
Yogesh Sonvane ◽  
K.A. Nekrasov ◽  
A.S. Boyarchenkov ◽  
A. Ya. Kupryazhkin ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Ab Initio
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