Crystalline solids bonding structures

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. 

For a substance to dissolve in a liquid, it must be capable of disrupting the solvent structure and permit the bonding of solvent molecules to the solute or its component ions. The forces binding the ions, atoms or molecules in the lattice oppose the tendency of a crystalline solid to enter solution. The solubility of a solid is thus determined by the resultant of these opposing effects. The solubility of a solute in a given solvent is defined as the concentration of that solute in its saturated solution. A saturated solution is one that is in equilibrium with excess solute present. The solution is still referred to as saturated, even... 

The structure of AICI3 is similarly revealing. The crystalline solid has a layer lattice with 6-coordinate Al but at the mp 192.4° the stmcture changes to a 4-coordinate molecular dimer Al2Clg as a result there is a dramatic increase in volume (by 85%) and an even more dramatic drop in electrical conductivity almost to zero. The mp therefore represents a substantial change in the nature of the bonding. The covalently bonded... 

Six members of this series could be isolated in modest yields as highly air-sensitive, dark blue or dark purple crystalline solids for which analytical, spectroscopic, and single-crystal X-ray analyses were fully consistent with the side-on-biidged N2 structures shown in Scheme 102. These complexes show unusual structural features as well as a unique reactivity. An extreme degree of N = N bond elongation was manifested in rf(N-N) values of up to 1.64 A, and low barriers for N-atom functionalization allowed functionalization such as hydrogenation, hydrosilylation, and, for the first time, alkylation with alkyl bromides at ambient temperature. ... 

Figure 11. Hydrogen-bonded structure of Imi-2 (two imidazoles spaced by two ethylene oxide (EO) repeat units) (a) in the crystalline state, as revealed by an X-ray structure analysis,and (b) in the liquid state (schemati-cal), as suggested by an NMR study.Note that the hydrogen bonds in the solid state are long-lived, whereas the hydrogen bonding in the molten state is highly dynamic (see text).

Here, p(r) is the average density of atoms found in a thin shell at a radius r from an arbitrary atom in the material, and p is the average density of the entire material. For very small values of r, g(r) —> 0, since atoms cannot overlap one another. For large values of r, on the other hand, g(r) —> 1, because atoms that are separated from one another by large distances in a disordered material are not influenced by one another. The distribution functions calculated by Lewis et al. for liquid and amorphous InP are shown in Fig. 9.4. As might be expected, the amorphous material has considerably more structure than the liquid. One important feature in the amorphous material is the peak in the P-P distribution near r 2.2 A. This peak shows the existence of P-P bonds in the amorphous material, a kind of bond that does not exist in the crystalline solid. 

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