Nonmolecular compounds

The calculation of atomization energies of nonmolecular solids is summarized in Tables II for fiuorides. III for chlorides, IV for bromides, V for iodides, VI for oxides, VII for sulfides, and VIII for selenides. The successful application of Equation 2 to such a large number and variety of nonmolecular compounds strongly supports the coordinate covalent or coordinated polymeric model. It seems probable that more complex compounds such as sulfates and carbonates are also of this nature. 

The molecular formula of a compound indicates the total numbers of different atoms in a molecule of it. For molecular compounds, the molecular formula is determined from the empirical formula and the molecular mass of the compound. For nonmolecular compounds, it is set at the empirical formula multiplied by infinity, representing a very large number (Chap. 5). 

Homoleptic silver(I) thiolates AgSR have been known and used for a long time,957,958 but until recently with little definitive information about their structures. They are insoluble or slightly soluble, yielding unreliable high molecular weights in solution, indicative of nonmolecular crystal structures. These compounds dissolve due to the presence of thiolate ions. 

Attempts have been made to obtain the nonmolecular form of nitrogen by pressurizing solid sodium azide—that is, a compound where nitrogen is present in another molecular form as a linear triatomic species N3, with the expectation that the different starting molecular stmcture could facilitate the polymerization. On the other hand, one could also note that the nitride ion is isoelectronic with... 

Hundreds of inorganic structure types are known. UnfoiTunately, it is only possible to present a limited number of them here. The strucmres of several nonmolecular solids that are of historical or pedagogical significance, or which are presently of significant technological interest have been chosen for description however, a large number of omissions is inevitable. There are examples of ionic, covalent, and metallic compounds that exist for almost every stmcture type. Thus, the common practice of classifying the stmcture types themselves as ionic, covalent, or metallic is not followed in this text. It should also be noted that many stmcture types are common to both iono-covalent and intermetallic compounds. 

The primary amides of the group 2 elements, M(NH2)2, are nonmolecular species. " When the NH2 ligand is replaced by the bulky bis(trimethylsilyl)amido group, however, molecular complexes are formed. A complete set of structures has been obtained for Be through Ba (Table 11). The barium bis(trimethylsilyl)amides form a progression of compounds that illustrate the important relationship between ligand bulk and metal nuclearity. The base-free compound, [Ba N(SiMe3)2 ]2, exists as a dimer that can accommodate... 

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. 

Although molecules have a fixed formula and composition, many nonmolecular solids are found to exist over a range of compositions. This variation is considered normal in alloys but unusual in nonme-tallic compounds such as oxides. However, not aU such solids have a definite and fixed formula, especially at high temperatures. Nonmetallic materials with a composition range are called nonstoi-chiometric compounds. Two ways in which this composition variation can occur are described below. 

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