Nonmolecular solids

Let us consider a species ML (metal-ligands). This species may be present in a nonmolecular solid or in a solution, it may be a molecule or a coordination complex ion. 

For nonmolecular solids, called coordinated polymers, he substitutes the Madelung part of the lattice energy... 

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. 

Most chemists are well acquainted with LCAO-MO theory. The numbers of atomic orbitals, even in large molecules, however, are miniscule compared to a nonmolecular solid, where the entire crystal can be considered one giant molecule. In a crystal there are in the order of 10 atomic orbitals, which is, for all practical purposes, an infinite number. The principle difference between applying the LCAO approach to solids, versus molecules, is the number of orbitals involved. Fortunately, periodic boundary conditions allow us to smdy solids by evaluating the bonding between atoms associated with a single lattice point. Thus, the lattice point is to the solid-state scientist, what the molecule is to the chemist. 

The study of optical centers and the influence of their immediate surroundings on their properties has proceeded successfully during the last decade. Not only has new fundamental knowledge been obtained, but also many new applications have been proposed and realized. The border lines between the different fields in which these centers are investigated, viz., the nonmolecular solid state, the molecular state (as solid or as solution), and the biochemical molecular state, are slowly fading. Stronger interactions between these fields might well be profitable to all of them. 

For application to nonmolecular solids, the bond description is similar but certain modifications are needed. First, the covalent energy must be multiplied by the equivalent number n of two electron covalent bonds per formula unit that must be broken for atomization. The evaluation of n will be discussed in detail presently. Second, the ionic energy must be evaluated as the potential energy over the entire crystal, corrected for the repulsions among adjacent electronic spheres. This is done by using the Born-Mayer equation for lattice energy, multiplying this expression by an empirical constant, a, which is 1 for the halides and less than 1 for the chal-cides, as follows ... 

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. 

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. 

One of the following will not contribute to the polarisability of a nonmolecular solid in a static electric field ... 

This approach has been fashioned in the pursuit of molecular rhenium chalcogenide clusters whose structures have not been accessible by conventional self-assembly techniques. The method, which has been termed cluster excision, involves the addition of a suitable ligand to the nonmolecular solid, such that the vacant sites on the metal centers will be occupied upon cleavage of the bridging interactions. Ligands that have been utilized in this approach include Cl and CN , affording molecular rhenium sulfide and selenide clusters (Equation (21)). This method also allows access to previously known structures under milder synthetic conditions ... 

Kume T, Ohuya Y, Nagata M et al (2007) Transformation of carbon dioxide to nonmolecular solid at room temperature and high pressure. J Appl Phys 102 053501... 

Chemical Description. The constituents of the system include atoms, ions, molecules as well as molecular and nonmolecular solids. The homogeneous catalytic reaction of interest occurs in the multicomponent liquid phase Pl- By definition, all the molecular and ionic species S involved directly in the catalysis are soluble in this liquid phase. In particular, one or more organic reagents must be present in Pl- The liquid phase must contain numerous soluble transition-metal... 

Section 9.5 extends the discussion to nonmolecular solids (network covalent, ionic, and metallic). 

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