Molecular solids linear

Pure NI3 has not been isolated, but the structure of its well-known extremely shock-sensitive adduct with NH3 has been elucidated — a feat of considerable technical virtuosity.Unlike the volatile, soluble, molecular solid NCI3, the involatile, insoluble compound [Nl3.NH3] has a polymeric structure in which tetrahedral NI4 units are comer-linked into infinite chains of -N-I-N-I- (215 and 230 pm) which in turn are linked into sheets by I-I interactions (336 pm) in the c-direction in addition, one I of each NI4 unit is also loosely attached to an NH3 (253 pm) that projects into the space between the sheets of tetra-hedra. The stmcture resembles that of the linked Si04 units in chain metasilicates (p. 349). A further interesting feature is the presence of linear or almost linear N-I-N groupings which suggest the presence of 3-centre, 4-electron bonds (pp. 63, 64) characteristic of polyhalides and xenon halides (pp. 835-8, 897). 

To make phenolic resins, you have to first make a phenolic prepolymer, which may be in a liquid or solid form. This can be accomplished by using either a base or an acid catalyst. The prepolymer is a low molecular weight, linear polymer that—and this is the whole key to phenolics—can be further processed at a time of the processors choosing to give the cross-linked phenolic resin.-All you need is a little more heat and pressure. The reactions are shown in abbreviated form in Figure 24-1,... 

Esters. Neopentyl glycol diesters are usually liquids or low melting solids. Polyesters of neopentyl glycol, and in particular unsaturated polyesters, are prepared by reaction with polybasic acids at atmospheric pressure. High molecular weight linear polyesters (qv) are prepared by the reaction of neopentyl glycol and the ester (usually the methyl ester) of a dibasic acid through transesterification (37—38). The reaction is usually performed at elevated temperatures, in vacuo, in the presence of a metallic catalyst. 

Similarly, expanding the KS potential in an LCAO expansion makes molecular density-functional calculations practical [9]. For metals and similar crystalline solids, it is best to expand the Kohn-Sham potential in momentum space via Fourier coefficients. For molecular solids various real-space method are under investigation. For molecules studied with the big, well-chosen Gaussian basis sets of quantum chemistry, it is undoubtedly best to expand the KS potential in linear-combination-of-Gaussian-type-orbital (LCGTO) form [10]. 

In the examples of our work on organic molecular and polymeric solids that follow, first some contributions to the UPS line widths in condensed molecular solids are discussed for two prototype systems, anthracene and isopropyl benzene then the UPS of two.aromatic pendant group polymers, polystyrene and poly(2-vinyl pyridine), are discussed and compared with some spectra concerning the simplest linear conjugated polymer, polyacetylene. 

Figure 30. Mobility, g, plotted linearly in In, as a function of electric field strength (E), plotted as for holes in tri-/ -tolylamine (TTA) (40 wt.%) in bisphenol-A polycarbonate. The range of field strengths is approximately 10 -10 V cm (1-100 V pm ). The mobility depends exponentially on With increasing temperature, the overall magnitude of/r increases while the dependence on E weakens. These dependences are observed in nearly all amorphous molecular solids. (Reprinted with permission from Ref. [73r].)...

The modest a-jt overlap in open-shell molecular solids suggests an approach based on separated molecular fragments Structural and spectroscopic evidence supports the occurrence of essentially unperturbed molecules or molecular ions in the solid state. Since valence-bond (VB) treatments of molecules become exact in the dissociated-atom limit, a diagrammatic VB approach has been developed for open-shell molecular solids. The resulting correlated crystal states are simply weighted linear combinations of VB structures for the entire solid. 

There are numerous theoretical and experimental results demonstrating that simple molecular solids transform into nonmolecular phases at high pressures and temperatures, ranging from monatomic molecular solids such as sulfur [61], phosphorous [62] and carbon [63] to diatomic molecular solids such as nitrogen [8, 9,40], carbon monoxide [12] and iodine [20, 21], to triatomic molecules such as ice [24, 25], carbon dioxide [10, 31, 37] and carbon disulfide [64, 65] to polyatomics such as methane [27, 28] and cyanogen [11], and aromatic compounds [29]. In this section, we will limit our discussion within a few molecular triatomics first to review the transformations in two isoelectronic linear triatomics, carbon dioxide and nitrous dioxide, and then to discuss their periodic analogies to carbon disulfide and silicone dioxide. 

Carbon dioxide molecule is the simplest form of linear molecular triatomics abundant in nature. At ambient temperatures, it crystallizes into cubic Pa-3) phase I, known as dry ice , at around 1.5 GPa and then to orthorhombic phase III Cmca) above 12 GPa (see Figs. 4 and 5). Both of these structures commonly appear in many other molecular solids [76, 77], for which stabilities have been well understood in terms of the intermolecular quadrupole-quadrupole interaction. In these phases at relatively low pressures below 15 GPa, the nearest intermolecular separation is in a range of 3.0 to 2.5 A, typically 2 - 2.5 times of the... 

For molecules and molecular solids these requirements seem almost inevitably to lead to an atomic orbital basis concept. Of course this is no new invention in the field. However, it is well known that minimal basis sets, to be used in the context of linear combinations of atomic orbitals (LCAO) can be optimized significantly for each class of bonds. A simple test demonstrates that different types of bonds have different optimum minimal basis sets, even if these are numerically defined. For calculations not relying on expertise or specific optimization, a minimal basis set is not sufficient. A question is whether the wish can be fulfilled with a function set twice as big as the minimal one for the valence orbitals. Investigation convinced the author that this is the case to a surprisingly large extent. 

The ability of resorcinol to function as a linear template to organize reactants in the solid state for [2 + 2] photoreaction also led to a molecular solid-state synthesis by design.Specifically, cocrystallization of lA-bis[2-(4-pyridyl)ethenyl]benzene (1.4-bpeb) with 5-methoxy-resorcinol (5-OMe-res) yielded a four-component assembly. 2(5-OMe-res) 2(1,4-bpeb), wherein four olefins, as two reaction centers, conformed to the topochemical principle. UV irradiation of the solid produced, regio- and stereoselectively. a targeted [2.2]paracyclophane (yield 60%) (Fig. 4c). 

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