A Novel Heterooctametallic Metallacarborane Tetramer

1999 ◽  
Vol 64 (5) ◽  
pp. 819-828 ◽  
Author(s):  
Keith G. Parker ◽  
J. Monte Russell ◽  
Michal Sabat ◽  
Russell N. Grimes
Keyword(s):  
Molecular Geometry ◽  
Crystalline Solid ◽  
Covalent Bonds ◽  
Cluster Chemistry ◽  
X Ray ◽  
Boron Cluster ◽  
Double Decker ◽  
Ruthenium Atom ◽  
Yellow Orange

The synthesis and X-ray crystal structure determination of [(2,3-Et2C2B4H4)Co(2,3-Et2C2B3H3-5-Bu)Ru]4 (3) are reported. Complex 3 was obtained serendipitously in low yield from a reaction of [(η4-C8H12)Ru(MeCN)4][PF6]2 with the (Et2C2B4H4)Co(Et2C2B3H3Bu)2- anion in THF solution at room temperature. The molecular geometry of 3, isolated as a yellow-orange crystalline solid, is without precedent in boron cluster chemistry and consists of an array of four (Et2C2B4H4)Co(Et2C2B3H3Bu)Ru units linked via intercluster Ru-B covalent bonds. Each cluster moiety contains a double-decker (C2B4)Co(C2B3) sandwich with an exo-polyhedral ruthenium atom occupying a "wedging" position in which it is bound to the C2B3 and the C2B4 ligands as well as to a neighboring sandwich unit.

scholarly journals X-RAY DETERMINATION OF THE STRUCTURE OF ANHYDROUS DIPHENYLCYCLOPROPENONE. VARIATIONS OF THE MOLECULAR GEOMETRY DUE TO HYDROGEN BONDING

1974 ◽  
Vol 3 (6) ◽  
pp. 639-642 ◽  
Author(s):  
Harumichi Tsukada ◽  
Hirotaka Shimanouchi ◽  
Yoshio Sasada
Keyword(s):  
Hydrogen Bonding ◽  
Molecular Geometry ◽  
X Ray

Six pyrimidonium salts: determination of their crystal structures and studies of their prototropic behaviour in solution

1984 ◽  
Vol 62 (6) ◽  
pp. 1194-1202 ◽  
Author(s):  
Thomas W. S. Lee ◽  
Steven J. Rettig ◽  
Ross Stewart ◽  
James Trotter
Keyword(s):  
Hydrogen Exchange ◽  
Molecular Geometry ◽  
High Reactivity ◽  
Methyl Groups ◽  
Contributing Factors ◽  
X Ray ◽  
X Ray Crystallography ◽  
Reactive Compound ◽  
Chloride Salts

Six methyl-substituted 2-pyrimidonium chloride salts have been prepared and the rates of hydrogen exchange of their reactive methyl groups (at the 4- and 6-positions) have been determined in DCl/D2O solution. Adjacent methyl groups, whether on nitrogen or carbon, activate the exchanging centres, whereas more distant methyl groups have a deactivating effect. The molecular geometry of the salts has been determined by X-ray crystallography with the view to determining whether the presence of strain in the pyrimidonium ring can account for the activating effect of adjacent methyl. The most reactive compound, the 1,5,6-trimethylpyrimidonium chloride, has a geometry that is consistent with high reactivity, viz. a non-planar ring and short H … H intermethyl distance. However, the 1,4,5,6-tetramethyl compound, which also is non-planar and has an extremely short 5-6 intermethyl distance (1.99 Å), is not highly reactive; that is, the heightened strain is unable to overcome the deactivating inductive effect of the additional methyl group. We conclude that deviations from ring planarity and short intermethyl distances are insufficient to account for the activation produced by adjacent methyl though they appear to be contributing factors to this effect.

Eine unerwartet stabile Sulfensäure: 4,6-Dimethoxy-1,3,5-triazin-2-sulfensäure; Synthese, Eigenschaften, Molekül- und Kristallstruktur / Unexpectedly Stable Sulfenic Acid: 4,6-Dimethoxy-1,3,5-triazine-2-sulfenic Acid; Synthesis, Properties, Molecular and Crystal Structure

1993 ◽  
Vol 48 (9) ◽  
pp. 1212-1222 ◽  
Author(s):  
Robert Tripolt ◽  
Ferdinand Belaj ◽  
Edgar Nachbaur
Keyword(s):  
Ionization Constant ◽  
Acid Synthesis ◽  
Crystalline Solid ◽  
Sulfenic Acid ◽  
X Ray ◽  
Nmr Data ◽  
Exact Determination ◽  
Synthesis Properties ◽  
C Nmr

4,6-Dimethoxy-1,3,5-triazine-2-sulfenic acid (1) was prepared by the reaction of 4,6-dimethoxy-1,3,5-triazine-2(1H)-thion (3) with 2-benzenesulfonyl-3-(p-nitrophenyl)-oxaziridine (2) in THF solution and isolated as a stable crystalline solid. The new compound was characterized by analytical and spectroscopic data (IR, 1H and 13C NMR, UV, MS) supported by MNDO-PM 3 calculations. UV spectrometry was used for exact determination of the ionization constant of 1(pKa = 5.86 ± 0.02 at 20°C). According to 13C NMR data and X-ray analysis the sulfenic acid 1 adopts the sulfenyl structure (R—SOH) in the condensed phase.Crystal data of 1 (90 K): a = 8.418(3), b = 21.289(6), c = 4.411(1) Å, Z = 4, P 21212, R = 0.0304, Rw = 0.0354 for 4105 unique reflections and 122 parameters. In the crystal, the molecules form dimers by two strong intermolecular O—H ••• N hydrogen bonds. The 6-membered ring shows alternating C—N bond lengths and is almost planar. The experimental electron deformation density (EDD) decreases in the order C—N > C—O ≈ C—S > S—O and is described in detail for the vicinity of the S atom.

On the transferability of QTAIMC descriptors derived from X-ray diffraction data and DFT calculations: substituted hydropyrimidine derivatives

2011 ◽  
Vol 67 (5) ◽  
pp. 425-436 ◽  
Author(s):  
A. A. Rykounov ◽  
A. I. Stash ◽  
V. V. Zhurov ◽  
E. A. Zhurova ◽  
A. A. Pinkerton ◽  
...  
Keyword(s):  
Electron Density ◽  
Density Functional ◽  
Molecular Structures ◽  
X Ray Diffraction ◽  
Covalent Bonds ◽  
Functional Theory ◽  
X Ray ◽  
Biginelli Compounds ◽  
Empirical Corrections

The combined study of electron-density features in three substituted hydropyrimidines of the Biginelli compound family has been fulfilled. Results of the low-temperature X-ray diffraction measurements and density functional theory (DFT) B3LYP/6-311++G** calculations of these compounds are described. The experimentally derived atomic and bonding characteristics determined within the quantum-topological theory of atoms in molecules and crystals (QTAIMC) were demonstrated to be fully transferable within chemically similar structures such as the Biginelli compounds. However, for certain covalent bonds they differ significantly from the theoretical results because of insufficient flexibility of the atom-centered multipole electron density model. It was concluded that currently analysis of the theoretical electron density provides a more reliable basis for the determination of the transferability of QTAIMC descriptors for molecular structures. Empirical corrections making the experimentally derived QTAIMC bond descriptors more transferable are proposed.

History of Rubber Research

2000 ◽  
Vol 73 (3) ◽  
pp. 405-426 ◽  
Author(s):  
Herbert Morawetz
Keyword(s):  
Elemental Composition ◽  
Chemical Structure ◽  
Biosynthetic Pathway ◽  
Low Molecular Weight ◽  
Covalent Bonds ◽  
Chain Molecules ◽  
X Ray ◽  
Covalently Bonded ◽  
History Of

Abstract After the discovery of the tapping of Hevea rubber trees in the middle of the eighteenth century and early technological applications of Hevea rubber, efforts to discover the chemical nature of rubber started with the determination of its elemental composition in 1826. Later it was shown that rubber pyrolysis yields low molecular weight chemicals with the identical elemental composition. It was long believed that these add to each other by “secondary valence bonds.” However Staudinger's work starting in 1920 proved that Hevea (H.) rubber consists of chains linked by covalent bonds. The utility of rubber increased dramatically with the discovery of vulcanization by Goodyear in 1844. However the nature of this process remained for many years controversial due to the influence of the “colloid school” of chemistry. The first observations on the nature of rubber elasticity date back to 1805, but more than a century passed before it was shown that the retractive force of stretched rubber is entropic. X-ray crystallographic studies not only provided the ultimate proof that natural rubber consists of covalently bonded chain molecules, but also gave evidence for its chemical structure. A century ago it was found that polymeric products other than H. rubber exhibited similar elastic properties. The race to produce synthetic rubbers was largely stimulated by the two World Wars. The availability of 14C labeled precursors led to the detailed description of the biosynthetic pathway by which rubber is produced in the Hevea plant.

Lateral resolution of the electron microbeam analysis

1978 ◽  
Vol 36 (1) ◽  
pp. 542-543
Author(s):  
H.J. Dudek
Keyword(s):  
Quantitative Analysis ◽  
Depth Resolution ◽  
Lateral Resolution ◽  
Cylindrical Particle ◽  
Correction Procedure ◽  
X Ray ◽  
Element Concentrations ◽  
Microbeam Analysis ◽  
The Matrix

The chemical inhomogenities in modern materials such as fibers, phases and inclusions, often have diameters in the region of one micrometer. Using electron microbeam analysis for the determination of the element concentrations one has to know the smallest possible diameter of such regions for a given accuracy of the quantitative analysis.In th is paper the correction procedure for the quantitative electron microbeam analysis is extended to a spacial problem to determine the smallest possible measurements of a cylindrical particle P of high D (depth resolution) and diameter L (lateral resolution) embeded in a matrix M and which has to be analysed quantitative with the accuracy q. The mathematical accounts lead to the following form of the characteristic x-ray intens ity of the element i of a particle P embeded in the matrix M in relation to the intensity of a standard S

Sem and X-Ray Analysis of Renal and Biliary Calculi

1976 ◽  
Vol 34 ◽  
pp. 306-307
Author(s):  
R. J. Narconis ◽  
G. L. Johnson
Keyword(s):  
Chemical Constituents ◽  
Natural State ◽  
X Ray Diffraction ◽  
Chemical Methods ◽  
X Ray ◽  
Additional Dimension ◽  
Biliary Calculi ◽  
Calculus Formation ◽  
Scanning Electron

Analysis of the constituents of renal and biliary calculi may be of help in the management of patients with calculous disease. Several methods of analysis are available for identifying these constituents. Most common are chemical methods, optical crystallography, x-ray diffraction, and infrared spectroscopy. The application of a SEM with x-ray analysis capabilities should be considered as an additional alternative.A scanning electron microscope equipped with an x-ray “mapping” attachment offers an additional dimension in its ability to locate elemental constituents geographically, and thus, provide a clue in determination of possible metabolic etiology in calculus formation. The ability of this method to give an undisturbed view of adjacent layers of elements in their natural state is of advantage in determining the sequence of formation of subsequent layers of chemical constituents.

Preparation And elemental analysis of ancient fibers

1987 ◽  
Vol 45 ◽  
pp. 410-411
Author(s):  
Allen Angel ◽  
Kathryn A. Jakes
Keyword(s):  
Cross Sections ◽  
Physical Structure ◽  
Energy Dispersive ◽  
Archaeological Sites ◽  
X Ray ◽  
Long Term Storage ◽  
Backscattered Electron ◽  
Electron Imaging

Fabrics recovered from archaeological sites often are so badly degraded that fiber identification based on physical morphology is difficult. Although diagenetic changes may be viewed as destructive to factors necessary for the discernment of fiber information, changes occurring during any stage of a fiber's lifetime leave a record within the fiber's chemical and physical structure. These alterations may offer valuable clues to understanding the conditions of the fiber's growth, fiber preparation and fabric processing technology and conditions of burial or long term storage (1).Energy dispersive spectrometry has been reported to be suitable for determination of mordant treatment on historic fibers (2,3) and has been used to characterize metal wrapping of combination yarns (4,5). In this study, a technique is developed which provides fractured cross sections of fibers for x-ray analysis and elemental mapping. In addition, backscattered electron imaging (BSI) and energy dispersive x-ray microanalysis (EDS) are utilized to correlate elements to their distribution in fibers.

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