Crystalline solids X-rays

It should also be noted here that recent work in Japan has shown that a free germanium cation can be prepared and structurally characterized. Thus, the reaction of tetrakis (tri-z-butylsilyl)cyclotrigermene with trityl tetraphenylborate affords (t-Bu3SiGe)3+ BPI14 as a yellow crystalline solid. X-ray crystallography shows that there is no close interaction between the anion and the cation. The stability of the compound is presumably due not only to the steric protection afforded by the bulky t-BtcSi substituents, but also to the fact that it contains a 2jr-electron aromatic ring.198... 

In the pure state n-butyl-, sec-butyl-, and iso-butyl lithiums are liquids at ambient temperatures, whereas methyl-, ethyl- and f-butyl lithiums are crystallinic solids. X-ray studies revealed that the crystals of methyl lithium are built of tetramers132, 135) a similar structure was deduced for /-butyl lithium128,133) whereas a layer structure, still built of tetrameric units, was proposed for ethyl lithium136). The inability of n-propyl-, n-butyl-, iso-butyl-, sec-butyl-, and amyl-lithium to crystallize seems to be caused by steric factors. 

The product is a black-brown solid that is very sensitive to oxygen. The same cation can be obtained by oxidation of S4N4 with AsFs and is unusual in being the only sulfur-nitrogen (paramagnetic) radical that has been obtained as a stable crystalline salt. X-ray diffraction analysis shows the structure to be a planar 5-membered ring with approximate... 

Because X-ray powder diffraction deals with solid samples, the analytical variables are different from those associated with the analysis of liquid or solution samples. Principle among these are particle size effects, uniform sample surface, crystallinity and X-ray absorption. Although particle size and a non-uniform sample surface are serious problems, their... 

All the solid phases were identified and characterized for crystallinity by X-ray powder diffraction (Philips PW 1730/10 diffractometer, Cu Kq radiation equipped with a PW 1030/70 vertical goniometer and connected to a P.C. computer for quantitative analyses). Crystallinities for Nu-10 and cristobalite were computed by comparing the intensity of the most characteristic diffraction peaks of each sample to that of the corresponding pure 100% crystalline phases used as standards. In some cases calibration curves derived from Nu-10/cristobalite mechanical mixtures were used. Si, Al, and alkali contents were determined either on precursors or calcined samples (900 C, air flow, 4h) by atomic absorption, using a Perkin-Elmer 380 AA instrument after digestion and dissolution of the samples in H,S04/HF solutions and further elimination of HF by gentle heating at 60 C for 12 n. 

IR and Raman are sensitive to the rotation and vibration of molecules in solid phases (crystalline or x-ray amorphous). Molecular units of similar structure and composition absorb IR radiation in the same energy range, usually independent of the larger structure of the material this property makes IR spectroscopy useful for studying molecules in the interfacial region such as surface hydroxyl groups and As oxoanions on mineral surfaces, and for fingerprinting the local environment of As in aystalline... 

Self-assembly of aromatic (and aliphatic) di-iodoperfluorocarbons, with derivatives of anilines which serve as electron donor partners, produces solid crystalline materials. X-ray diffraction agrees with the structure reported in Scheme 23. 

This chapter has concentrated on crystalline materials. X-ray diffraction can also furnish structural information about amorphous and semi-amorphous solids, even though the structure is much more diffuse. 

Polymer VII from 1,4-Cyclohexanedione and 1,2,4,5-Tetrakis-(hydroxymethvl) cyclohexane. Into a 100—ml flask equipped with a mag. stirrer, a Dean-Stark trap, a reflux condenser and a drying tube were added 50 ml of dry n-butyl ether, 2.04 g of 1,2,4,5-tetrakis(hydroxymethyl)cyclohexane and 1.12 g of 1,4-cyclohexanedione. The solution-suspension was heated under reflux for 12 hours followed by the addition of 0.1 g of -toluenesulfonic acid. After the mixture was heated overnight, it was cooled to room temperature. The mixture was filtered with suction and the resulting solid was washed well with n-butyl ether. After most of the ether was removed, the solid was washed with water, acetone and finally ether. The solid, which was dried over P2O5 and under 0.2 mm pressure, weighted 3.1 g (99%). The solid was soluble only in hexafluoroisopropanol and had an [T ] of 0.04 dl/g at 25°c. The polymer was found to be crystalline by X-ray and did not melt. 

Since its discovery in 1912 by von l.aue. X-ray diffraction has provided a wealth of important information to science and industry. For example, much of what is known about the arrangement and the spacing of atoms in crystalline materials has been determined directly from diffritciion studies. In addition, such studies have led to a much clearer tinderstftnding of the physical properties of metals, polymeric materials, and other solids. X-ray diffraction is one of the ntost important methods for determining the structures of such complex natural products as steroids, vittimins, and an tibtoiics. The details of these applications are beyxmd the scope of this book. 

Systematic investigation of the solid phases formed in the system SOj-HjO (Erametsa et al., 1972) has shown the composition of the major solid phase to correspond to the trisulfite complex found by Vickery in solution. When R is Sm, Gd, or Dy, (NH )3R(S03)3-HjO may be prepared as crystalline precipitate. X-ray powder diffraction studies indicated that this compound has two crystalline modifications the low-temperature a-form, best obtained around room temperature, and the high temperature or p-form, crystallized at temperatures 50°C higher. 

XRD techniques are used mainly to study the crystal structure of crystalline solids at the elec-trode solution interface. Structural changes, solid-state reactions, precipitation processes, dissolution processes, and intercalation processes can be followed as a function of applied potential and time. For non-crystalline samples. X-ray absorption and EXAFS allow the structure to be studied in more detail. 

Because x-rays are particularly penetrating, they are very usefiil in probing solids, but are not as well suited for the analysis of surfaces. X-ray diffraction (XRD) methods are nevertheless used routinely in the characterization of powders and of supported catalysts to extract infomration about the degree of crystallinity and the nature and crystallographic phases of oxides, nitrides and carbides [, ]. Particle size and dispersion data are often acquired with XRD as well. 

Solids can be crystalline, molecular crystals, or amorphous. Molecular crystals are ordered solids with individual molecules still identihable in the crystal. There is some disparity in chemical research. This is because experimental molecular geometries most often come from the X-ray dilfraction of crystalline compounds, whereas the most well-developed computational techniques are for modeling gas-phase compounds. Meanwhile, the information many chemists are most worried about is the solution-phase behavior of a compound. 

Cane sugar is generally available ia one of two forms crystalline solid or aqueous solution, and occasionally ia an amorphous or microcrystalline glassy form. Microcrystalline is here defined as crystals too small to show stmcture on x-ray diffraction. The melting poiat of sucrose (anhydrous) is usually stated as 186°C, although, because this property depends on the purity of the sucrose crystal, values up to 192°C have been reported. Sucrose crystallines as an anhydrous, monoclinic crystal, belonging to space group P2 (2). 

From shock compression of LiF to 13 GPa [68] these results demonstrate that X-ray diffraction can be applied to the study of shock-compressed solids, since diffraction effects can be observed. The fact that diffraction takes place at all implies that crystalline order can exist behind the shock front and the required readjustment to the shocked lattice configuration takes place on a time scale less than 20 ns. Another important experimental result is that the location of (200) reflection implies that the compression is isotropic i.e., shock compression moves atoms closer together in all directions, not just in the direction of shock propoagation. Similar conclusions are reached for shock-compressed single crystals of LiF, aluminum, and graphite [70]. Application of these experimental techniques to pyrolytic BN [71] result in a diffraction pattern (during compression) like that of wurtzite. 

EXAFS is a nondestructive, element-specific spectroscopic technique with application to all elements from lithium to uranium. It is employed as a direct probe of the atomic environment of an X-ray absorbing element and provides chemical bonding information. Although EXAFS is primarily used to determine the local structure of bulk solids (e.g., crystalline and amorphous materials), solid surfaces, and interfaces, its use is not limited to the solid state. As a structural tool, EXAFS complements the familiar X-ray diffraction technique, which is applicable only to crystalline solids. EXAFS provides an atomic-scale perspective about the X-ray absorbing element in terms of the numbers, types, and interatomic distances of neighboring atoms. 

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