Preferred orientation, solid state

Crystallography is a very broad science, stretching from crystal-structure determination to crystal physics (especially the systematic study and mathematical analysis of anisotropy), crystal chemistry and the geometrical study of phase transitions in the solid state, and stretching to the prediction of crystal structures from first principles this last is very active nowadays and is entirely dependent on recent advances in the electron theory of solids. There is also a flourishing field of applied crystallography, encompassing such skills as the determination of preferred orientations, alias textures, in polycrystalline assemblies. It would be fair to say that... 

Metallurgists originally, and now materials scientists (as well as solid-state chemists) have used erystallographic methods, certainly, for the determination of the structures of intermetallic compounds, but also for such subsidiary parepistemes as the study of the orientation relationships involved in phase transformations, and the study of preferred orientations, alias texture (statistically preferential alignment of the crystal axes of the individual grains in a polycrystalline assembly) however, those who pursue such concerns are not members of the aristocracy The study of texture both by X-ray diffraction and by computer simulation has become a huge sub-subsidiary field, very recently marked by the publication of a major book (Kocks el al. 1998). 

In the case of the smaller macrocycle [13]aneN4, six configurational isomers exist for [Ni([13]aneN4)]2+ due to the orientation of the N—H protons above or below the plane of the macrocycle. X-ray crystallography and NMR spectroscopy, respectively, revealed that the R,iS,7 ,iS -[Ni([13]aneN4)]2+ form (trans- ) is the preferred one both in aqueous solution and in the solid state.1 43... 

Recently, the X-ray crystal structure of (164) has been completed, and it confirmed the syn conformational preference of the subheterocyclic rings in the solid state (82UP52200). The related —CH2SCH2— bridged analog of (164) has been shown to possess a similar orientation (82UP52200). 

Fig. 5.7 shows schematically the potential across a semiconductor-electrolyte interface. To understand it we have to take two additional effects into account. First, the liquid molecules usually show a preferred orientation at the surface. Their dipole moment causes a jump of the potential. Second, on a solid surface the electrons can occupy surface states. These extra electrons contribute to the potential. 

We can then treat e as a scalar quantity, which is independent of the orientation of the electric field vector, as in Equation (2.6). This will not be true if the polymer has a preferred orientation conferred either by mechanical deformation or solid-state polymerisation. In this situation the relative permittivity will be a tensor so that... 

Both A A and cis trans equilibria of siderophore complexes can exist in solution. The chirality of the ligand can impose a preferred metal-center chirality. In addition, the degree of this preference depends on the stereochemical rigidity of the ligand. In principle, the magnitude of the molar circular dichroism can be used as a measure for diastereoisomeric equilibria based on a comparison of the solid-state and solution ellipticity. Nevertheless, predictions of metal-center chiralities require theoretical calculations. For example, empirical-force-field calculations of iron(III) enterobactin show that the A orientation at the metal center is more stable than the A by 0.5 kcalmoH, which is consistent with the CD spectra. ... 

In addition to structure elucidation by NMR, X-ray crystallographic investigations have been performed to elucidate the structures of several toxaphene congeners in the solid state. Information about symmetry, space group, bond lengths, bond angles, and preferred orientation of the substituents on primary carbons in the solid state can be obtained [47,126,127]. It was found that B7-515 (P-32) crystallizes in orthorhombic form, B8-1413 (P-26) and B9-1025 (P-62) triclinic, and B9-1679 (P-50) monoclinic [126,127]. 

The preparation of samples for powder diffraction can lead to variations and inconsistencies among measurements on the same sample (e.g. Potts et al. 1994). Jenkins and Snyder (1996) have summarized the possible causes for compositional variations between the original sample and that prepared for the diffraction experiment grinding of the sample (generally required to reduce preferred orientation) vide infra can lead to amorphism, strain in individual particles, decomposition, solid state reaction or... 

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