Single-Crystal X-Ray Diffractometry

Fourier transformation. The electron density map shows the location of atoms. A 2D electron density map is produced for each angle. The computer program uses the 2D maps plus the rotation angle data to generate the 3D coordinates for atoms (molecules, ions) in the crystal. The mathematical treatment of the experimental data to produce a crystal structure from an unknown single-crystal diffraction pattern is complicated and beyond the scope of this text, but an example of the results will be shown in the following. 

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Another characteristic point is the special attention that in intermetallic science, as in several fields of chemistry, needs to be dedicated to the structural aspects and to the description of the phases. The structure of intermetallic alloys in their different states, liquid, amorphous (glassy), quasi-crystalline and fully, three-dimensionally (3D) periodic crystalline are closely related to the different properties shown by these substances. Two chapters are therefore dedicated to selected aspects of intermetallic structural chemistry. Particular attention is dedicated to the solid state, in which a very large variety of properties and structures can be found. Solid intermetallic phases, generally non-molecular by nature, are characterized by their 3D crystal (or quasicrystal) structure. A great many crystal structures (often complex or very complex) have been elucidated, and intermetallic crystallochemistry is a fundamental topic of reference. A great number of papers have been published containing results obtained by powder and single crystal X-ray diffractometry and by neutron and electron diffraction methods. A characteristic nomenclature and several symbols and representations have been developed for the description, classification and identification of these phases. 

A last point that should be raised with regard to validation is that any comparison between theory and experiment must proceed in a consistent fashion. Consider molecular geometries. Chemists typically visualize molecules as having structure . Thus, for example, single-crystal X-ray diffractometry can be used to determine a molecular structure, and at the end of a molecular mechanics minimization one has a molecular structure, but is it strictly valid to compare them ... 

The conformation of this flexible ligand in solution must be different fro that in the crystalline state. In general, to correlate CD spectra with structures] that are revealed by single-crystal x-ray diffractometry, it is desirable to measure not only the solution but also the microcrystalline CD, although great care is] required for the latter experiment. In this regard, our newly developed diffusfj reflectance CD spectrophotometer is ideal. 

Single crystals of PrMnOs and TbMnO, were grown by floating zone method and the crystal structure was determined by single crystal X-ray diffractometry. The structure of these compounds belongs to the orthorhombic system (space group is Pnma, No. 62) with the lattice parameters... 

A single crystal. X-ray diffractometry experiment has shown that Wlt/ -CjMes)) / -COCH2CMe2Ph)(CH2CMe2Ph)(NO) contains an t/ -bonded acyl, which is quite unusual for W(II). The CO insertion of reaction (g) thus corresponds to a 16-electron 18-electron conversion. This W(II) system is unusual because CO insertions are seldom encountered with tungsten it is possible that in this case, and similar ones, preliminary CO coordination (the starting compounds do not contain coordinated CO) is favored by a delocalization of an electron pair onto the nitrosyl ligand... 

The technique used involves extremely long times (e.g. single-crystal X-ray diffractometry). 

X-ray diffraction is a formidable tool for the examination of crystalline material. The theory and practice of single-crystal X-ray diffractometry will be covered here only briefly, since there are many reference sources for in-depth information [15-20],... 

More recently, Muniz and coworkers prepared the stable bis(sulfonyUmide) derived amidoiodanes 458 and 459 by treatment of (diacetoxyiodo)benzene with bis(tosylimide) or bis(methanesulfonylimide) (Scheme 2.131) [616-618]. The structure ofbis(tosylimide) 458 was established by single-crystal X-ray diffractometry... 

Goto, A., Hondoh, T., and Mae, S. 1990. The electron density distribution in ice Ih determined by single-crystal X-ray diffractometry. J. Chem. Phys. 93 1412-1417. 

In contrast, the rare earth hexacyanometallates have been studied in detail by a number of techniques, including single-crystal X-ray diffractometry. These compounds have also found applications in the separation and purification of the rare earths by fractional crystallization. 

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