Lead compounds solid-state products

The electrides. Following many experimental difficulties, Dye and coworkers were able to demonstrate that reaction of 18-crown-6 with caesium in a 1 2 ratio (under specified conditions) leads to isolation of shiny, black crystals of a product of composition Cs+(18-crown-6)2 (El-laboudy, Dye Smith, 1983 Dye Ellaboudy, 1984). The solid-state 133Cs nmr spectrum, the esr spectrum, and the magnetic susceptibility of this product all indicated that it was of type Cs+(l8-crown-6).e" that is, a crystalline electride in which the anion is a single electron. In overall terms, this exotic class of compound may be considered to lie on the border between metals and non-metals. 

In the solid state, both 46 and 47 exist as bent monomeric sandwich complexes with ring centroid-lead-ring centroid angles of 152.2° in 46 and 144.2° in 47. Interestingly, if the reaction between PbCl2 and [Li(dme)2][/Bu2G2P3] is carried out in tmen rather than DME, the product formed is not a homoleptic plumbylene but rather the novel heterobimetallic compound 48.73... 

Many reactions that proceed with elimination of a gas (N2, COz, etc.) and formation of radical-pair intermediates show considerable stereochemical differences in solution and in the crystal. Thus, solid-state photolysis of the diaza compound 176 yields, among other products, cis-1,2-diphenylcyclopentane, 177 no trans isomer, 178, has been detected. Irradiation of 176 in solution leads to mixtures in which the trans product 178 predominates (244). 

A third type of internal solid state reaction (see later in Fig. 9-12) is characterized by two (solid) reactants A and B which diffuse into a crystal C from opposite sides. C acts as a solvent for A and B. If the reactants form a stable compound AB with each other (but not with the solvent crystal C), an internal solid state reaction eventually takes place. It occurs in the solvent crystal at the location of maximum supersaturation of AB by internal precipitation and subsequent growth of the AB particles. Similar reactions can be observed on a crystal surface which, in this case, plays the role of the solvent matrix C. Surface transport of the reactants leads to a product band precipitated on the surface at some distance from each of the two reactants and completely analogous to the internal reactions described before. In addition, internal reactions have also been observed if (viscous) liquids are chosen as the reaction media (C). 

Based on some interesting reactions in certain inorganic crystalline compounds, Kohlschutter [9,10] proposed that the nature and properties of the products obtained take place on the surface or within the solid state. Indeed, he coined the term topochemistry for such reactions in the solid state. However, systematic investigations of photoinduced reactions in crystals began from 1964 onward by Schmidt and Cohen [11], Their studies on the 2tt + 2tt photoreaction of cinnamic acid derivatives in the crystalline state and correlation with the molecular organization in these crystals led to what are now known as Topochemical Principles. The most important conclusions reached by them are as follows (1) The necessary conditions for the reactions to take place are that the reactive double bonds are parallel to one another and the center-to-center distance be within 4.1 A (2) there is one-to-one correspondence between the stereochemistry of the photoproduct and the symmetry relationship between the reactants. The centrosymmet-ric relationship (called the a-form) leads to centrosymmetric cyclobutane (anti-HT), whereas the mirror symmetric arrangements (called the (5-form) produce mirror symmetric dimer (yy -HH). 

Organoindium substances are important, especially for the production of materials by metal-organic chemical vapor-phase deposition (MOCVD). This technique involves the thermal decomposition of mixtures of an organoindium compound and a compound such as phosphine (PH3), leading to the deposition of ordered layers of InP. The resulting compound can be used in the formation of semiconductors and solid-state optical devices (similar to silicon), see also Inorganic Chemistry. 

A dione 74 also undergoes ODPM rearrangement under direct irradiation to give compound 75 in 94% yield (Scheme 4.30) [44]. The product 75 was crystallized from ethyl acetate/hexane at room temperature to lead to two polymorphs. Polymorphism is recognized as being a vital branch of solid-state supramolecular chemistry. 

One of the best-studied solid-state reactions is the photopolymerization of distyrylpyrazine (9) and related compounds to give crystalline polymers containing cyclobutane rings (Scheme 10). This reaction is reminiscent of Schmidt s early work on cinnamic acids, although the presence of two double bonds per monomer can lead to oligomeric or polymeric rather than solely dimeric products. The four-center reaction of 9, and other related polymerizations, have been reviewed in detail by Hasegawa, who has played a central role in the study of these systems... 

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