Crystalline solid structures

At this point, there is worth, since having the geometric information characteristic to a crystalline solid structure, to give a uniform classification of the chemical compounds (inoiganic, organic, and mineral) with respect to the space group where the crystalline solid of the compound can be... 

Recently, Hoffmann et al. [12] have described the molecular and crystalline solid structure of 2-n-nonyl-1,4-phenylene bis(4-n-octyloxybenzoate), as estimated using X-ray diffraction [12]. The observed structure deviates from the model for the nematic phase in the crystalline solid state, as the lateral chains exist in -trans conformation. The type of link between the lateral hydrocarbon chain and the mesogenic core influences the course of the clearing points. A comparison performed for the 2-alkyl, acyl and alkyloxycarbonyl substituted derivatives 2a-2c in Table 1 showed a break in the clearing-point curve at 2b and 2c for five single units (including the -CO- or -CO-0 groups) within the lateral chains. The lower the transition temperatures the more pronounced the break in the curve [13, 15]. 

Figure 5. Space-filling model of the crystalline solid structure of 4-nitrobenzyl 2,5-bis(4-ethoxybenzoyl-oxy )benzoate having a three-unit spacer. (Reproduced by permission of Hoffmann et al. [67]).

The three-dimensional synnnetry that is present in the bulk of a crystalline solid is abruptly lost at the surface. In order to minimize the surface energy, the themiodynamically stable surface atomic structures of many materials differ considerably from the structure of the bulk. These materials are still crystalline at the surface, in that one can define a two-dimensional surface unit cell parallel to the surface, but the atomic positions in the unit cell differ from those of the bulk structure. Such a change in the local structure at the surface is called a reconstruction. 

Dinitrogeri pentoxide is the anhydride of nitric acid and is prepared by removing water from pure nitric acid by means of phosphorus (V) oxide. It is a crystalline solid having the ionic structure of (N02) (N03) , nitronium nitrate (the nitronium ion is mentioned later). It decomposes above 273 K, thus ... 

Clinoptilolite is microporous crystalline solid with well-defined structure, which have great potential for a number of applications in various fields, such as adsorption, separation, ion-exchange and catalysis. 

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. 

Camphor was originally obtained from the camphor tree Lauras eamphora in which it appeared in the optically active dextro-rotary form. Since about 1920 the racemic ( ) mixture derived from oil of turpentine has been more generally used. By fractional distillation of oil of turpentine the product pinene is obtained. By treating this with hydrochloric acid, pinene hydrochloride (also known as bomyl chloride) may be produced. This is then boiled with acetic acid to hydrolyse the material to the racemic bomeol, which on oxidation yields camphor. Camphor is a white crystalline solid (m.p. 175°C) with the structure shown in Figure 22.3. 

Calculations for Ceo in the LDA approximation [62, 60] yield a narrow band (- 0.4 0.6 eV bandwidth) solid, with a HOMO-LUMO-derived direct band gap of - 1.5 eV at the X point of the fee Brillouin zone. The narrow energy bands and the molecular nature of the electronic structure of fullerenes are indicative of a highly correlated electron system. Since the HOMO and LUMO levels both have the same odd parity, electric dipole transitions between these levels are symmetry forbidden in the free Ceo moleeule. In the crystalline solid, transitions between the direct bandgap states at the T and X points in the cubic Brillouin zone arc also forbidden, but are allowed at the lower symmetry points in the Brillouin zone. The allowed electric dipole... 

It is one of the wonders of the history of physics that a rigorous theory of the behaviour of a chaotic assembly of molecules - a gas - preceded by several decades the experimental uncovering of the structure of regular, crystalline solids. Attempts to create a kinetic theory of gases go all the way back to the Swiss mathematician, Daniel Bernouilli, in 1738, followed by John Herapath in 1820 and John James Waterston in 1845. But it fell to the great James Clerk Maxwell in the 1860s to take... 

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 singlet-level theories have also been applied to more sophisticated models of the fluid-solid interactions. In particular, the structure of associating fluids near partially permeable surfaces has been studied in Ref. 70. On the other hand, extensive studies of adsorption of associating fluids in a slit-like [71-74] and in spherical pores [75], as well as on the surface of spherical colloidal particles [29], have been undertaken. We proceed with the application of the theory to more sophisticated impermeable surfaces, such as those of crystalline solids. 

There is no evidence for the tellurium analogues ArN=Te, but the cyclic trimers (EN Bu)3 (E = Se, Te) are stable crystalline solids that have been structurally characterized (Section 6.3). 

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... 

This last reaction is typical of many in which F3CIO can act as a Lewis base by fluoride ion donation to acceptors such as MF5 (M = P, As, Sb, Bi, V, Nb, Ta, Pt, U), M0F4O, Sip4, BF3, etc. These products are all white, stable, crystalline solids (except the canary yellow PtFe ) and contain the [F2CIO] cation (see Fig. 17.26h) which is isostructural with the isoelectronic F2SO. Chlorine trifluoride oxide can also act as a Lewis acid (fluoride ion acceptor) and is therefore to be considered as amphoteric (p. 225). For example KF, RbF and CsF yield M [F4C10] as white solids whose stabilities increase with increasing size of M+. Vibration spectroscopy establishes the C4 structure of the anion (Fig. 17.29g). 

The Lewis structure of the PCI, molecule is shown in (22), and we see that it obeys the octet rule. However, when phosphorus trichloride reacts with more chlorine (Fig. 2.10), phosphorus pentachloride, a pale yellow crystalline solid, is produced ... 

FIGURE 5-16 Crystalline solids have well-defined faces and an orderly internal structure. Each face of the crystal is formed by the top plane of an orderly stack of atoms, molecules, or ions. 

A crystalline solid is a solid in which the atoms, ions, or molecules lie in an orderly array (Fig. 5.16). A crystalline solid has long-range order. An amorphous solid is one in which the atoms, ions, or molecules lie in a random jumble, as in butter, rubber, and glass (Fig. 5.17). An amorphous solid has a structure like that of a frozen instant in the life of a liquid, with only short-range order. Crystalline solids typically have flat, well-defined planar surfaces called crystal faces, which lie at definite angles to one another. These faces are formed by orderly layers of atoms (Box 5.1). Amorphous solids do not have well-defined faces unless they have been molded or cut. 

The starting point for the synthesis of xenon compounds is the preparation of xenon difluoride, XeF2, and xenon tetrafluoride, XeF4, by heating a mixture of the elements to 400°C at 6 atm. At higher pressures, fluorination proceeds as far as xenon hexafluoride, XeFfi. All three fluorides are crystalline solids (Fig. 15.27). In the gas phase, all are molecular compounds. Solid xenon hexafluoride, however, is ionic, with a complex structure consisting of XeF< + cations bridged by F anions. 

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. ... 

Complexes of molybdenum in the lower valence-states of -t 2 and + 3 have been produced only in the past two years. For the Mo(II) species, the usual starting-material is Mo2(acetate>4. Reaction of this with KS2COEt in THF gives two products, a green complex tentatively assigned as [Mo2(Etxant>4], which solvates to form the red complex [Mo2(Etxant)4(THF)2]. The structure of the latter complex was elucidated by X-ray analysis 169). Steele and Stephenson 170) were also able to synthesize a red, crystalline solid (methanol solution), which they formulated as [Mo(Etxant)2]2 (XI), and reacted this with Lewis bases, e.g., pyridine, to form [Mo(Etxant)2L]2- Thus, there appears to be a difference between the two compounds formulated as [Mo2(Et-xant)2]2 that... 

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