Halide dielectric properties

If ion pairs but not free ions are formed, the extent of ion pair formation may be estimated from the dielectric properties of the solution. This method has been used in studying the effect of Lewis acids on alkyl halides.164... 

Holes. Compared to the situation for photoelectrons in the silver halides, the properties of holes are less well understood. In the effective mass approximation, the binding energy is moderated by the background dielectric constant. When a mobile carrier is close to a trapping center, it does not experience the full dielectric constant of the perfect lattice. If the effective mass is sufficiently large or the dielectric constant sufficiently small, the... 

The indirect technique derives from a study of dielectric properties adopted after the study by Breckenridge of the defect constitution in alkali halide crystals. When the dielectric properties of an oxide film are examined critically with respect to the dielectric constant 6, conductivity a, resistivity / , and loss tangent tan 5 as a function of frequency, then results resembling the idealized curves of Fig. 3 can be anticipated. The detailed analysis of these curves has been considered by many authors and recently summarized by Volger and Gray ( ). The analyses can be modified for a variety of conditions with or without the coexistence of interfacial polarization. This technique has been extensively applied by Pryor and co-workers (27,28 technique is rapidly finding new adherents (29,3o ... 

The rigid-ion model is also inconsistent with the dielectric properties of crystals (Sect.4.3.2). At optical frequencies only the electrons (and not the ions) respond to the electric field of the light. The electronic polarization gives rise to the dielectric constant which for the alkali halides have observed values between 2 and 3. Since the rigid-ion model ignores the electronic polarizabilities, it predicts = 1. 

The dipole moments of the hydrogen halides decrease with increasing atomic number of the hydrogen, the largest difference occurring between HF and HCl, and association of molecules is not an important factor in the properties of FICl, HBr and HI. This change in dipole moment is reflected in the diminishing permittivity (dielectric constant) values from HF to HI. 

The other hydrogen halides are less tractable as solvents, as might be expected from their physical properties (p. 813), especially their low bps, short liquid ranges, low dielectric constants and negligible self-dissociation into ions. Nevertheless, they have received some attention, both for comparison with HF and as preparative media with their own special advantages.In particular, because of their low bp and consequent ease of removal, the liquid HX solvent systems have provided convenient routes to BX4, BF3C1 ,... 

Some recent studies have underlined the effect that certain physical properties of the reaction medium have in governing the nature and yields of the products obtained when indole Grignard reagents react with alkyl or alkynyl halides. Such factors include the basicity and dielectric constant of the medium and its ability to solvate any of the reacting species. ... 

The properties of HF reflect the strong hydrogen bonding that persists even in the vapor state. As a result of its high polarity and dielectric constant, liquid HF dissolves many ionic compounds. Some of the chemistry of HF as a nonaqueous solvent has been presented in Chapter 10. Properties of the hydrogen halides are summarized in Table 15.9. 

In several previous papers, the possible existence of thermal anomalies was suggested on the basis of such properties as the density of water, specific heat, viscosity, dielectric constant, transverse proton spin relaxation time, index of refraction, infrared absorption, and others. Furthermore, based on other published data, we have suggested the existence of kinks in the properties of many aqueous solutions of both electrolytes and nonelectrolytes. Thus, solubility anomalies have been demonstrated repeatedly as have anomalies in such diverse properties as partial molal volumes of the alkali halides, in specific optical rotation for a number of reducing sugars, and in some kinetic data. Anomalies have also been demonstrated in a surface and interfacial properties of aqueous systems ranging from the surface tension of pure water to interfacial tensions (such as between n-hexane or n-decane and water) and in the surface tension and surface potentials of aqueous solutions. Further, anomalies have been observed in solid-water interface properties, such as the zeta potential and other interfacial parameters. 

Table III lists some of the physical properties of polymers which contain ethylenebis [tris (2-cyanoethyl) phosphonium bromide]. This additive caused an increase in the dissipation factor and dielectric constant and lowered the dielectric strengths of polyethylene and poly (methyl methacrylate). The effects on mechanical properties were mixed. Obviously, lower concentrations of phosphonium halides would have less effect on mechanical and electrical properties. At levels of 1-3% very little change in properties would be expected. It was surprising that the phosphonium salts were compatible with such a range of polymers. We did not observe any tendency for the phosphonium salts to plate out of or exude from the polymer. In all cases homogeneous blends were obtained.

Preparation and properties of alkoxide halides of antimony(V) of the type (RO)nSbX5 n (n = 1-4) have been described in a number of publications24 -258. These compounds exist in dimeric form. The chloroantimony ethoxides, (EtO)nSbCl5 n, ionize in the solvents of high dielectric constants259,260 ... 

Mayer [22], the above correlations indeed work well and are quite useful for predicting values such as the free energy of salt solutions and complex formation in various solvents. Another typical example of the importance of the use of DN and AN as solvent parameters, instead of properties such as the dielectric constant, would be ion pair association constants in isodielectric solvents. For instance, as shown by Mayer [15], association constants of various perchlorates isocyanates, and halides (alkali metal, ammonium, and tetraalkyl ammonium cations) are very different in isodielectric solvents such as nitromethane (DN = 2.7), acetonitrile (DN = 14.1), and DMF (DN = 26.6), whose dielectric constant is around 26 at room temperature. 

Systematic investigations of complex equilibria in a variety of solvents of different dielectric and solvating properties are still scarce. The most informative study so far seems to be that performed by Luehrs, Iwamoto, and Kleinberg (93) on the solubility of silver halides, and the... 

Defects in Solids Dielectric Polarizabilities of Oxides Fluorides Diffraction Methods in Inorganic Chemistry Electronic Stmcture of Solids Fluorides Solid-state Chemistry Halides Solid-state Chemistry Intercalation Chemistry Non-crystalUne Solids Oxides Solid-state Chemistry Phosphates Solid-state Chemistry Polyphosphazenes Sol-Gel Synthesis of Solids Solids Computer Modeling Stmcture Property Maps for Inorganic Solids Zeolites. 

A transformation will be regarded as a thermolysis if the halocyclopropane is heated either neat, in the gas phase or in an inert solvent. This solvent should neither serve as a nucleophile HY, nor have a high dielectric constant (to favor cation formation). If the solvent does have one or both of the aforementioned properties, the transformation will be regarded as a solvolysis. Although all these methods in principle obey the same general rules vide supra), their synthetic results are clearly distinct. Conditions in thermolysis are harsh. Since there is no other nucleophile present, the allylic cation can only be trapped by the halide ion that has left the cyclopropane. At the elevated temperature of thermolysis, the resulting allylic halides... 

Ion solvation in polar solvents is also an important aspect of the subject matter considered here. This is traditionally studied by measuring the Gibbs energy and enthalpy of transfer of a variety of electrolytes from water to another polar solvent. Single ion quantities are then derived on the basis of the TATB assumption. Study of these quantities for simple monoatomic ions like the alkali metal cations and the halide anions leads to the conclusion that specific molecular properties, namely, Lewis acidity and basicity, are important in ion solvation. On the other hand, the dielectric permittivity, a non-specific bulk property. 

The silver halides, with the exception of one crystal modification of Agl, have cubic crystal structures. Crystal structure data, relevant lattice properties and low temperature dielectric constants, are collected in Table 3. AgF, AgCl, and AgBr all have the NaCl rocksalt structure in which there are four silver halide pairs per nonprimitive unit cell with cation-anion nearest neighbor distances equal to one-half a lattice constant. 

Both antimony tribromide and antimony triiodide are prepared by reaction of the elements. Their chemistry is similar to that of SbQ3 in that they readily hydrolyze, form complex halide ions, and form a wide variety of adducts with ethers, aldehydes, mercaptans, etc. They are soluble in carbon disulfide, acetone, and chloroform. There has been considerable interest in the compounds antimony bromide sulfide [14794-85-5], antimony iodide sulfide [13868-38-1], ISSb, and antimony iodide selenide [15513-79-8] with respect to their solid-state properties, ferroelectricity, pyroelectricity, photoconduction, and dielectric polarization. 

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