Solid-state structures ionic crystals

Heteropolyanions and isopolyanions are polymeric oxoanions (polyoxometalates) (2, 3, 5, 6). The structure of a heteropolyanion or polyoxoanion molecule itself is called a primary structure (5, 6, 77). There are various kinds of polyoxoanion structure (Section II.A. 1). In solution, heteropoly anions are present in the unit of the primary structure, being coordinated with solvent molecules and/ or protonated. Most heteropolyanions tend to hydrolyze readily at high pH (Section 1I.C). Protonation and hydrolysis of the primary structure may be major structural concerns in solution catalysis. Heteropoly compounds in the solid state are ionic crystals (sometimes amorphous) consisting of large polyanions, cations, water of crystallization, and other molecules. This three-dimensional arrangement is called the secondary structure. For understanding catalysis by solid heteropoly compounds, it is important to distinguish between the primary structure and the secondary structure (5, 6, 17). Recently, it has been realized that, in addition... 

The liquid state of ionic compounds seems also to be rather simply analyzed. The change from crystal to liquid is much less dramatic in ionic solids than in covalent solids, since the ionic crystal is already close-packed. The liquid is presumably a somewhat random, but locally neutral, conglomeration of ions. Most of the studies of ionic compounds made in this part of the book have not depended greatly on details of structure and so remain appropriate in the liquid. It should be noted, however, that for studies of transport and diffusion, one should... 

In the series of the binary halides of selenium and tellurium, the crystal structure determinations of tellurium tetrafluoride (100) and of tellurium tetrachloride on twinned crystals (65, 66) were the key to understanding the various and partly contradictory spectroscopic and other macroscopic properties (e.g., 66,161,168,169,219,220, 412), as well as the synthetic potential of the compounds. In contrast to the monomeric molecular i//-tbp gas phase structures with C2v symmetry (417), the solid state structures of both are polynuclear. As the prototype of the chlorides and bromides of selenium and tellurium, crystalline tellurium(IV) chloride has a cubane-like tetrameric structure with approximate Td symmetry (Fig. 1). Within the distorted TeCla+a octa-hedra the bonds to the triply bridging chlorine ligands are much longer than to the terminal chlorines. The bonding system can be described either covalently as Te4Cli6 molecules, or, in an ionic approximation, as [(TeCl Cn4] with a certain degree of stereochemical activity of the lone pairs toward the center of the voluminous cubane center (65, 66). 

A solid mixture is any mixture of crystals of different substances, regardless of its solid-state structure. It may be a simple mechanical mixture of component crystals, a mixed crystal, a molecular complex, or an ionic salt. In this chapter, a simple mechanical mixture as well as all uncharacterized two-component crystals are grouped under solid mixtures. 

As a starting point for considering the effect of impurity and solvent on crystallization, the growth and interaction process is examined in the framework of the fundamental solid-state, interfacial, and liquid phase (solute-solvent-impurity) chemistry. The solid-state chemistry is specific to a given crystalline material and the nature of the bonds (e.g., ionic, covalent, van der Waals, etc.) that hold the crystal structure together. A complete description of the solid-state aspects of crystal growth is beyond the scope of this... 

Crystal deconstruction is the process that leads backwards. in a reverse "aufbau process, from the structure of a molecular crystal to the component molecules or ions. Crystal deconstruction allows one to focus on the interactions that are more relevant for crystal structure cohesion. The objective of the deconstruction process is also that of learning about the factors responsible for molecular/ionic recognition and self-assembly in the solid state. Insights into crystal polymorphism can be gained by comparing the different distributions of intermolecular interactions associated with the existence of different crystal forms of the same molecular species. 

Wang, X., Vogel, C.S., Heinemann, F.W., Wasserscheid, P. and Meyer, K., Solid-state structures of double-long-chain imidazolium ionic liquids Influence of anion shape on cation geometry and crystal packing, Cryst. Growth Des. 11 (5), 1974-1988 (2011). 

In Chapter 6, we discuss solid state structures of metals and ionic compounds, and detail the unit cells of a number of prototype stuctures. The unit cell is the smallest repeating unit in a crystal lattice, and its dimensions are characteristic of a particular polymorph of a compound. A unit cell is characterized by three cell edge lengths (a, b and c) and three angles (a, (3 and 7). Distances are often given in the non-SI unit of the angstrom (A), because lA=10 °m and... 

A consideration of the lattice energies of transition metal compounds affords an explanation of the trends in the ionic radii of these elements as well as estimates of crystal field stabilization energies. This treatment offers a bridge between the sections (Chapters 2 through 6) on coordination compounds and those (Chapters 7 and 8) involving solid-state structures and energetics. 

Crystal structure, crystal defects and chemical reactions. Most chemical reactions of interest to materials scientists involve at least one reactant in the solid state examples inelude surfaee oxidation, internal oxidation, the photographie process, electrochemieal reaetions in the solid state. All of these are critieally dependent on crystal defects, point defects in particular, and the thermodynamics of these point defeets, especially in ionic compounds, are far more complex than they are in single-component metals. I have spaee only for a superficial overview. 

Recognizing Cause and Effect In a crystal lattice structure, the electrons are held tightly by the ions, which are rigidly held in place by electrostatic attraction. Discuss how this characteristic explains why ionic compounds generally (a) have high melting points and (b) do not conduct electricity in the solid state. 

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