Simulation of the Crystal-To-Amorphous Transformation in Irradiated Quartz

1990 ◽  
Vol 209 ◽  
Author(s):  
Uma Jain ◽  
Adam C. Powell ◽  
Linn W. Hobbs
Keyword(s):  
Crystal Structure ◽  
Structural Changes ◽  
Interatomic Distances ◽  
Computer Screen ◽  
Bond Lengths ◽  
Orthogonal Coordinates ◽  
Crystalline Matrix

ABSTRACTQuartz and other crystalline polymorphs of silica transform from the crystalline to an aperiodic state under irradiation. There is a need to understand the structural changes involved during this amorphization process. We have built an engineering modelwhich simulates the growth of amorphous regions within a crystalline matrix during the crystal-to-amorphous transition in irradiated quartz. The resulting crystal structure is displayed on the computer screen or plotted on a printer with the orthogonal coordinates of all the atoms in the cluster and the interatomic distances stored in a file. We find the bond lengths increase by about 3%, which is a reasonable value to expect since quartz expands 14% by volume during the amorphization. The results also show the crystal structure surrounding the strained region to be somewhat disturbed, consistent with what is observed experimentally.

Temperature dependence of the crystal structure of α-AgSCN by powder neutron diffraction

2007 ◽  
Vol 40 (6) ◽  
pp. 1039-1043 ◽  
Author(s):  
Darrick J. Williams ◽  
L. L. Daemen ◽  
S. C. Vogel ◽  
Th. Proffen
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Neutron Diffraction ◽  
Structural Changes ◽  
Rietveld Method ◽  
Tetrahedral Coordination ◽  
Bond Lengths ◽  
Powder Neutron Diffraction ◽  
Different Temperatures ◽  
Neutron Powder Diffractometer

A structural study of α-AgSCN was carried out using the neutron powder diffractometer HIPPO (high-pressure preferred orientation powder) at ten different temperatures between 25 and 275 K. The structure of α-AgSCN was refined using the Rietveld method and the symmetry elements for the material were found to be: space group No. 15,C2/c,a= 8.7210 (8) Å,b= 7.9318 (8) Å,c= 12.3329 (5) Å, β = 138.750 (3)°, volume = 562.497 (9) Å3andZ= 8. The Ag+cation has tetrahedral coordination and is surrounded by three –SCN thiocyanate ligands and one isothiocyanate –NCS ligand down to 25 K, with no structural changes. The bond lengths at 275 K are Ag—S1 = 2.749 (10), Ag—S2 = 2.995 (11), Ag—S3 = 2.411 (11), Ag—N = 2.150 (5), S—C = 1.783 (11) and C—N = 1.1447 (35) Å. The bond lengths at 25 K are Ag—S1 = 2.782 (5), Ag—S2 = 2.941 (5), Ag—S3 = 2.431 (5), Ag—N = 2.1526 (26), S—C = 1.749 (5) and C—N = 1.140 (2) Å.

scholarly journals Structural Changes in the Acceptor Site of Photosystem II upon Ca2+/Sr2+ Exchange in the Mn4CaO5 Cluster Site and the Possible Long-Range Interactions

Biomolecules ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 371
Author(s):  
Koua
Keyword(s):  
Crystal Structure ◽  
Photosystem Ii ◽  
Long Range ◽  
Electron Acceptor ◽  
Structural Changes ◽  
Acceptor Site ◽  
Oxygen Evolving Complex ◽  
Long Range Interactions ◽  
Structural Perturbations ◽  
Oxygen Evolving

The Mn4CaO5 cluster site in the oxygen-evolving complex (OEC) of photosystem II (PSII) undergoes structural perturbations, such as those induced by Ca2+/Sr2+ exchanges or Ca/Mn removal. These changes have been known to induce long-range positive shifts (between +30 and +150 mV) in the redox potential of the primary quinone electron acceptor plastoquinone A (QA), which is located 40 Å from the OEC. To further investigate these effects, we reanalyzed the crystal structure of Sr-PSII resolved at 2.1 Å and compared it with the native Ca-PSII resolved at 1.9 Å. Here, we focus on the acceptor site and report the possible long-range interactions between the donor, Mn4Ca(Sr)O5 cluster, and acceptor sites.

scholarly journals Crystal structure of K[Hg(SCN)3] – a redetermination

2014 ◽  
Vol 70 (9) ◽  
pp. i46-i46 ◽  
Author(s):  
Matthias Weil ◽  
Thomas Häusler
Keyword(s):  
Crystal Structure ◽  
Room Temperature ◽  
Three Dimensional ◽  
Lattice Parameters ◽  
Bond Lengths ◽  
Dimensional Network ◽  
Anisotropic Displacement Parameters ◽  
Precision And Accuracy ◽  
Standard Deviations ◽  
Atomic Coordinates

The crystal structure of the room-temperature modification of K[Hg(SCN)3], potassium trithiocyanatomercurate(II), was redetermined based on modern CCD data. In comparison with the previous report [Zhdanov & Sanadze (1952).Zh. Fiz. Khim.26, 469–478], reliability factors, standard deviations of lattice parameters and atomic coordinates, as well as anisotropic displacement parameters, were revealed for all atoms. The higher precision and accuracy of the model is, for example, reflected by the Hg—S bond lengths of 2.3954 (11), 2.4481 (8) and 2.7653 (6) Å in comparison with values of 2.24, 2.43 and 2.77 Å. All atoms in the crystal structure are located on mirror planes. The Hg2+cation is surrounded by four S atoms in a seesaw shape [S—Hg—S angles range from 94.65 (2) to 154.06 (3)°]. The HgS4polyhedra share a common S atom, building up chains extending parallel to [010]. All S atoms of the resulting1∞[HgS2/1S2/2] chains are also part of SCN−anions that link these chains with the K+cations into a three-dimensional network. The K—N bond lengths of the distorted KN7polyhedra lie between 2.926 (2) and 3.051 (3) Å.

scholarly journals N-(5-Chloro-1,3-thiazol-2-yl)-2,4-difluorobenzamide

2012 ◽  
Vol 68 (6) ◽  
pp. o1857-o1857 ◽  
Author(s):  
Xi-Wang Liu ◽  
Jian-Yong Li ◽  
Han Zhang ◽  
Ya-Jun Yang ◽  
Ji-Yu Zhang
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Benzene Ring ◽  
Dihedral Angle ◽  
Title Compound ◽  
Benzoyl Chloride ◽  
Bond Lengths ◽  
Compound C

The title compound, C10H5ClF2N2OS, was obtained by linking an amino heterocycle and a substituted benzoyl chloride. The dihedral angle between the two rings is 41.2 (2)° and the equalization of the amide C—N bond lengths reveals the existence of conjugation between the benzene ring and the thiazole unit. In the crystal, pairs of N—H...N hydrogen bonds link molecules into inversion dimers. Non-classical C—H...F and C—H...O hydrogen bonds stabilize the crystal structure.

Crystal structure of magnesium chromium vanadate Mg2CrV3O11, a member of the A2BV3O11 vanadate family

2007 ◽  
Vol 22 (3) ◽  
pp. 246-252 ◽  
Author(s):  
A. Worsztynowicz ◽  
S. M. Kaczmarek ◽  
W. Paszkowicz ◽  
R. Minikayev
Keyword(s):  
Crystal Structure ◽  
Rietveld Method ◽  
Ion Pairs ◽  
Exchange Constant ◽  
Type I ◽  
Type Ii ◽  
Paramagnetic Resonance ◽  
Interatomic Distances ◽  
Electron Paramagnetic ◽  
Full Occupancy

The crystal structure of recently discovered chromium (III) dimagnesium trivanadate (V) Mg2CrV3O11 was refined using the Rietveld method. The crystal system of Mg2CrV3O11 is triclinic with space group P1− (Mg1.7Zn0.3GaV3O11 type) and lattice parameters a=6.4057(1) Å, b=6.8111(1) Å, c=10.0640(2) Å, α=97.523(1)°, β=103.351(1)°, γ=101.750(1)°, and Z=2. The characteristic feature of compounds in the A2BV3O11 (A=Mg, Zn and B=Ga, Fe, Cr) family is a strong tendency to share the octahedral M(1) and M(2) sites by both divalent A and trivalent B atoms, and the bipyramidal M(3) sites occupied by divalent A ions. In the present refinement, the only constraint assuming full occupancy of the M(1), M(2), and M(3) sites leads to the following Cr/(Cr+Mg) ratios: 0.70(2) at M(1), 0.24(2) at M(2), and 0.03(2) at M(3). These occupancies are discussed and compared to those of isotypic compounds. The values of interatomic distances are found to be comparable with those reported by R. D. Shannon in 1976. Electron paramagnetic resonance has been also analyzed. Two absorption lines with g≈2.0 (type I) and g≈1.98 (type II) have been recorded in the EPR spectra, and attributed to V4+ ions and Cr3+–Cr3+ ion pairs, respectively. The exchange constant J between Cr3+ ions has been calculated.

Molecular orbital structures of sulfones

1982 ◽  
Vol 60 (6) ◽  
pp. 730-734 ◽  
Author(s):  
Russell J. Boyd ◽  
Jeffrey P. Szabo
Keyword(s):  
Crystal Structure ◽  
Gas Phase ◽  
Molecular Orbital ◽  
Geometry Optimization ◽  
Membered Ring ◽  
Molecular Orbital Calculations ◽  
Bond Lengths ◽  
Comparison With Experiment ◽  
The Difference

Abinitio molecular orbital calculations are reported for several cyclic and acyclic sulfones. The geometries of XSO2Y, where X, Y = H, F, or CH3 are optimized at the STO-3G* level. Similar calculations are reported for the smallest cyclic sulfone, thiirane-1,1 -dioxide, as well as the corresponding sulfoxide, thiirane-1-oxide, and the parent sulfide, thiirane. Where comparison with experiment is possible, the agreement is satisfactory. In order to consider the possibility of substantial differences between axial and equatorial S—O bonds in the gas phase, as observed in the crystal structure of 5H,8H-dibenzo[d,f][1,2]-dithiocin-1,1-dioxide, STO-3G* calculations are reported for a six-membered ring, thiane-1,1-dioxide, and a model eight-membered ring. Limited geometry optimization of the axial and equatorial S—O bonds in the chair conformations of the six- and eight-membered rings leads to bond lengths of 1.46 Å with the difference being less than 0.01 Å.

Investigations of Actinide Metals and Compounds under Pressure Provide Important Insights into Bonding and Chemistry

2003 ◽  
Vol 802 ◽  
Author(s):  
R. G. Haire ◽  
S. Heathman ◽  
T. Le Bihan ◽  
A. Lindbaum ◽  
M. Iridi
Keyword(s):  
Structural Changes ◽  
Chemical Properties ◽  
X Ray Diffraction ◽  
Interatomic Distances ◽  
X Ray ◽  
Effect Of Pressure ◽  
Electronic Configurations ◽  
5F Electrons ◽  
Actinide Series ◽  
Alloys And Compounds

ABSTRACTOne effect of pressure on elements and compounds is to decease their interatomic distances, which can bring about dramatic perturbations in their electronic nature and bonding, which can be reflected in changes in physical and/or chemical properties. One important issue in the actinide series of elements is the effect of pressure on the 5f-electrons. We have probed changes in electronic behavior with pressure by monitoring structure by X-ray diffraction, and have studied several actinide metals and compounds from thorium through einsteinium. These studies have employed angle dispersive diffraction using synchrotron radiation, and energy dispersive techniques via conventional X-ray sources. The 5f-electrons of actinide metals and their alloys are often affected significantly by pressure, while with compounds, the structural changes are often not linked to the involvement of 5 f-electron. We shall present some of our more recent findings from studies of selected actinide metals, alloys and compounds under pressure. A discussion of the results in terms of the changes in electronic configurations and bonding with regard to the element's position in the series is also addressed.

Improved synthesis and crystal structure of the parent 1,3,5-trisilacyclohexane

2016 ◽  
Vol 71 (1) ◽  
pp. 77-79 ◽  
Author(s):  
Eugen Weisheim ◽  
Hans-Georg Stammler ◽  
Norbert W. Mitzel
Keyword(s):  
Crystal Structure ◽  
Solid State ◽  
Electron Diffraction ◽  
Gas Phase ◽  
Gaseous Phase ◽  
Chair Conformation ◽  
Gas Electron Diffraction ◽  
State Structure ◽  
Synthesis And Crystal Structure ◽  
Bond Lengths

AbstractThe crystal structure and an improved synthesis of 1,3,5-trisilacyclohexane are reported. The solid state structure is compared with the reported structure determined in the gas phase by gas electron diffraction (GED). 1,3,5-Trisilacyclohexane adopts a chair conformation in the solid state. The Si–C bond lengths as well as all angles of 1,3,5-trisilacyclohexane in the solid state have similar dimensions compared to the structure in the gaseous phase.

scholarly journals Crystal structure of bis(2-{1-[(E)-(4-fluorobenzyl)imino]ethyl}phenolato-κ2N,O)palladium(II)

2015 ◽  
Vol 71 (4) ◽  
pp. 350-353
Author(s):  
Amalina Mohd Tajuddin ◽  
Hadariah Bahron ◽  
Hamizah Mohd Zaki ◽  
Karimah Kassim ◽  
Suchada Chantrapromma
Keyword(s):  
Crystal Structure ◽  
Schiff Base ◽  
Hydrogen Bonds ◽  
Dihedral Angle ◽  
Title Complex ◽  
Asymmetric Unit ◽  
Schiff Base Ligands ◽  
Bond Lengths ◽  
Square Planar ◽  
Coordination Plane

The asymmetric unit of the title complex, [Pd(C15H13FNO)2], contains one half of the molecule with the PdIIcation lying on an inversion centre and is coordinated by the bidentate Schiff base anion. The geometry around the cationic PdIIcentre is distorted square planar, chelated by the imine N- and phenolate O-donor atoms of the two Schiff base ligands. The N- and O-donor atoms of the two ligands are mutuallytrans, with Pd—N and Pd—O bond lengths of 2.028 (2) and 1.9770 (18) Å, respectively. The fluorophenyl ring is tilted away from the coordination plane and makes a dihedral angle of 66.2 (2)° with the phenolate ring. In the crystal, molecules are linked into chains along the [101] direction by weak C—H...O hydrogen bonds. Weak π–π interactions with centroid–centroid distances of 4.079 (2) Å stack the molecules alongc.

scholarly journals Dipotassium tetrahydroxidopentaoxidotetraborate monohydrate

IUCrData ◽  
2019 ◽  
Vol 4 (1) ◽  
Author(s):  
M. K. Dhatchaiyini ◽  
M. NizamMohideen ◽  
G. Rajasekar ◽  
A. Bhaskaran
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Coordination Number ◽  
Title Compound ◽  
Three Dimensional ◽  
Compound K ◽  
Bond Lengths ◽  
Dimensional Network

In the tetraborate anion of the title compound, K2[B4O5(OH)4]·H2O, the bridging B—O bond lengths of the tetrahedral BO4 and the trigonal-planar BO3 units are slightly longer than the corresponding terminal B—OH bond lengths. The crystal structure is stabilized by intermolecular O—H...O, O—H...Owater and Owater—H...O hydrogen bonds, generating a three-dimensional network. The two potassium cations both show a coordination number of 9.

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