3. Crystal structures

2016 ◽  
pp. 39-63
Author(s):  
A. M. Glazer
Keyword(s):  
Crystal Growth ◽  
Crystal Structures ◽  
Major Part ◽  
Chemical Substance ◽  
Close Packing ◽  
Stable Structure ◽  
Organic Crystal ◽  
Biological Molecules ◽  
Common Salt ◽  
Different Types

‘Crystal structures’ describes the different types of close packing—hexagonal, cubic, face-centred cubic, and body-centred cubic—used to describe many simple inorganic structures, especially those of the elements. The reason for atoms to pack so closely together is to form the densest array possible to provide a stable structure. The ability of a chemical substance to adopt different crystal structures is called polymorphism, as displayed by carbon. Examples of simple inorganic structures, such as common salt, are explained along with organic crystal structures, and the different methods of crystal growth. Crystallography has also played a major part in determining the structures and activities of large biological molecules like DNA, RNA, proteins, and viruses.

Crystal structure images of large gold clusters and growing crystals by HRTEM

1984 ◽  
Vol 42 ◽  
pp. 428-429
Author(s):  
L.R. Wallenberg ◽  
J.-O. Bovin ◽  
G. Schmid
Keyword(s):  
Crystal Structure ◽  
Nucleation And Growth ◽  
Close Packing ◽  
Gold Clusters ◽  
Molecular Weight Determination ◽  
Growth Mechanisms ◽  
Starting Point ◽  
Different Types ◽  
Nucleation And Growth Mechanisms ◽  
Points Of View

Metallic clusters are interesting from various points of view, e.g. as a mean of spreading expensive catalysts on a support, or following heterogeneous and homogeneous catalytic events. It is also possible to study nucleation and growth mechanisms for crystals with the cluster as known starting point.Gold-clusters containing 55 atoms were manufactured by reducing (C6H5)3PAuCl with B2H6 in benzene. The chemical composition was found to be Au9.2[P(C6H5)3]2Cl. Molecular-weight determination by means of an ultracentrifuge gave the formula Au55[P(C6H5)3]Cl6 A model was proposed from Mössbauer spectra by Schmid et al. with cubic close-packing of the 55 gold atoms in a cubeoctahedron as shown in Fig 1. The cluster is almost completely isolated from the surroundings by the twelve triphenylphosphane groups situated in each corner, and the chlorine atoms on the centre of the 3x3 square surfaces. This gives four groups of gold atoms, depending on the different types of surrounding.

Crystal Structures of Tetragonal NdPc2O and NdPc2Clx,O1-x Obtained from NdPc2H by Anodic Crystal Growth

1988 ◽  
Vol 156 (1) ◽  
pp. 247-256 ◽  
Author(s):  
Mireille Mossoyan-deneux ◽  
David Benlian ◽  
Andre Baldy ◽  
Marcel Pierrot
Keyword(s):  
Crystal Growth ◽  
Crystal Structures

Synthesis, crystal growth and characterization of 1,5-diphenylpenta-1,4-dien-3-one: An organic crystal

2011 ◽  
Vol 406 (22) ◽  
pp. 4195-4199 ◽  
Author(s):  
K. Vanchinathan ◽  
G. Bhagavannarayana ◽  
K. Muthu ◽  
S.P. Meenakshisundaram
Keyword(s):  
Crystal Growth ◽  
Organic Crystal

scholarly journals A computational study on how structure influences the optical properties in model crystal structures of amyloid fibrils

2017 ◽  
Vol 19 (5) ◽  
pp. 4030-4040 ◽  
Author(s):  
Luca Grisanti ◽  
Dorothea Pinotsi ◽  
Ralph Gebauer ◽  
Gabriele S. Kaminski Schierle ◽  
Ali A. Hassanali
Keyword(s):  
Optical Properties ◽  
Hydrogen Bonding ◽  
Proton Transfer ◽  
Crystal Structures ◽  
Amyloid Fibrils ◽  
Computational Study ◽  
Model Systems ◽  
Hydrogen Bonding Interactions ◽  
Model Crystal ◽  
Different Types

Different types of hydrogen bonding interactions that occur in amyloids model systems and molecular factors that control the susceptibility of the protons to undergo proton transfer and how this couples to the optical properties.

Organic Crystal Growth: Directly from Amorphous Solid Powder to Single Crystal

2021 ◽  
Author(s):  
Siyu Chen ◽  
Lin Zhu ◽  
Bingwen Zhang ◽  
Shu-Na Yun ◽  
Jinyi Wang ◽  
...  
Keyword(s):  
Crystal Growth ◽  
Single Crystal ◽  
Amorphous Solid ◽  
Organic Crystal

scholarly journals The sensory acceptability of a tilapia (Oreochromis niloticus) mechanically separated meat-based spread

2012 ◽  
Vol 15 (2) ◽  
pp. 166-173 ◽  
Author(s):  
Daniela De Grandi Castro Freitas ◽  
Alda Letícia da Silva Santos Resende ◽  
Angela Aparecida Lemos Furtado ◽  
Luana Tashima ◽  
Henrique Muniz Bechara
Keyword(s):  
Chemical Composition ◽  
Oreochromis Niloticus ◽  
Raw Material ◽  
Common Salt ◽  
Microbiological Analysis ◽  
Sensory Acceptability ◽  
Different Types ◽  
Adequate Quality ◽  
Mechanically Separated Meat ◽  
Hedonic Scale

Mechanically Separated Meat (MSM) is an alternative for the diversification of new fish-based products and also as a solution for the use of waste from the filleting industries. Tilapia MSM was used in this study for the formulation of a fish spread aimed at investigating its acceptability by consumers. Two spread formulations were prepared with different types of commercial salt: seasoned salt (A) and common salt (B). The consumers (112) evaluated their acceptance with respect to overall impression, spreadability, appearance and flavour acceptability on a 9-point hedonic scale. A microbiological analysis of the Tilapia MSM was also carried out and the chemical composition of the Tilapia MSM-based spread determined. When considering the acceptance of all the consumers, the overall impression, appearance and flavour were significantly (P < 0.05) lower for the spread made with common salt (B). However, three different consumer segments could be found from the overall impression of the Tilapia MSM-based spread. The largest segment also preferred the spread made with the seasoned salt (A), but both products were well accepted. The tilapia MSM presented adequate quality as a raw material according to the technical regulations for microbiological standards. The final product presented the following chemical composition: moisture - 62.17%; ash - 2.11%; protein - 9.75% and lipid - 18.81%. These results could be of great importance for the industry in developing and marketing new products obtained from mechanically separated Tilapia meat.

Synthese und Struktur von Nb0,89Fe0,93Te2 und Ta0,77Fe0,90Te2 / Synthesis and Structure of Nb0.89Fe0.93Te2 and Ta0.77Fe0.90Te2

1992 ◽  
Vol 47 (9) ◽  
pp. 1203-1212 ◽  
Author(s):  
Jörg Neuhausen ◽  
Karl-Ludwig Stork ◽  
Elisabeth Potthoff ◽  
Wolfgang Tremel
Keyword(s):  
Single Crystal ◽  
Crystal Structures ◽  
Chemical Transport ◽  
Structure Type ◽  
Close Packing ◽  
Hexagonal Close Packing ◽  
X Ray ◽  
The Relationship

Nb0.89Fe0.93Te2 and Ta0.77Fe0.90Te2 were prepared by chemical transport reactions. The crystal structures of both compounds were determined using X-ray single crystal methods. The structures of the layer compounds Nb0.89Fe0.93Te2 (Pmna, Z = 2, a = 7.951(1) Å, b = 7.241(1) A, c = 6.233(1) Å) and Ta0.77Fe0.90Te2 (Pmna, Z = 2, a = 7.890(2) Å, b = 7.252(2) Å, c = 6.192(1) Å) are based on a hexagonal close packing of Te atoms. Approximately one-half of the octahedral holes in this packing are occupied by Nb (Ta) atoms, about one-quarter of the tetrahedral holes are occupied by Fe atoms. The relationship to the NiAs structure type is discussed.

scholarly journals Validation of experimental molecular crystal structures with dispersion-corrected density functional theory calculations

2010 ◽  
Vol 66 (5) ◽  
pp. 544-558 ◽  
Author(s):  
Jacco van de Streek ◽  
Marcus A. Neumann
Keyword(s):  
Density Functional Theory ◽  
Crystal Structures ◽  
Density Functional ◽  
Unit Cell ◽  
Organic Crystal ◽  
Large Temperature ◽  
Unit Cell Parameters ◽  
Functional Theory ◽  
Cell Parameters ◽  
Experimental Crystal

This paper describes the validation of a dispersion-corrected density functional theory (d-DFT) method for the purpose of assessing the correctness of experimental organic crystal structures and enhancing the information content of purely experimental data. 241 experimental organic crystal structures from the August 2008 issue of Acta Cryst. Section E were energy-minimized in full, including unit-cell parameters. The differences between the experimental and the minimized crystal structures were subjected to statistical analysis. The r.m.s. Cartesian displacement excluding H atoms upon energy minimization with flexible unit-cell parameters is selected as a pertinent indicator of the correctness of a crystal structure. All 241 experimental crystal structures are reproduced very well: the average r.m.s. Cartesian displacement for the 241 crystal structures, including 16 disordered structures, is only 0.095 Å (0.084 Å for the 225 ordered structures). R.m.s. Cartesian displacements above 0.25 Å either indicate incorrect experimental crystal structures or reveal interesting structural features such as exceptionally large temperature effects, incorrectly modelled disorder or symmetry breaking H atoms. After validation, the method is applied to nine examples that are known to be ambiguous or subtly incorrect.

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