Polarizing action

In any case, the polarizing action upon the material by a given generator must be followed in more detail. In density matrix evolution, each specified field action transfonns either the ket or the bra side of the density... 

Criterion b demands detectability of the chemisorbed species of the poison. This point is particularly important in the case of proton acids, since the lifetime of protonated species may be very low due to the high mobility of surface protons. Thus, the pyridinium ion cannot be detected on silica surfaces, although some protonated species must have been formed (399), as can be shown from a continuous absorption in the infrared spectra. Protons that can hardly be detected directly by protonated probe molecules may well initiate catalytic reactions due to their polarizing action during their fluctuations (349,350). 

Fig. 3.7.5. Dependence of pPN of some metal-oxides in the molten KCl-NaCl equimolar mixture at 700 °C against polarizing action of the cations by Goldschmidt (Zrk 2).

Thus, the electronegativity values are linearly dependent on a parameter similar to the polarizing action of the cation. The dependence of the solubility on the Allred-Rochow electronegativity is divided into two sharply bounded and practically linear plots with close slopes for 3d-elements and for alkaline-earth metal-oxides (see Fig. 3.7.13). Since the slopes of these dependences are close, different positions of these plots may be explained by different relationships between the nuclear charge and Z for metals characterized by different electronic configurations. From the above-said it may be concluded that in high-temperature alkali-metal halide melts a correlation of metal-oxide solubilities with the crystal-lochemical radii of the cations is considerably simpler, i.e. it does not require the introduction of any corrections of the nucleus charge, such as Z. ... 

If the chemisorption and concurrent ring cleavage of the lactone occurred through the polarizing action of the cations, then the position of the equilibrium between structures A and B would depend upon the size of the cations and would be shifted to the left with increasing size. Hence, on lithium chloride the lactone would be more strongly chemi-... 

As noted above, Kossel introduced the idea that the transition from ionic to covalent substances is gradual, the covalence increasing with the mutual polarizing influence of ions. This idea was developed by Fajans and his school who defined the polarizabilities of ions and estimated the polarizing action of cations (Z/r ), but ultimately failed to create a quantitative theory. The reason is obvious [10] there are no completely ionic substances, only intermediate cases, more or less approaching this type. Hence the parameters of ideal ions are not available experimentally, the more so since ionic radii cannot be uniquely defined from interatomic distances (see Chap. 1). Thus the polarization concept remained only qualitative. However, the contribution in the bond energy of the polarizing effect of atoms can be described in the form that has proven itself for the van der Waals interaction (see Sect. 4.4), where the deviation of the A B distance from the mean of A A and B B distances is a function of the difference of the atomic polarizabilities... 

Instead, for CaCOj, Figure 4.54, the polarization in the lattice is asymmetrical a ion of carbon due to the big positive charge and the small radius, has a polarizing action much larger than the ion of Ca. As a result, the electron shell of will be deformed, meaning the movement towards in other words, the electronic density is mainly located along the bond C-0. The overlapping of valence orbital of the two ions leads to the reduction of the distance between them with the formation of a covalent bond. 

The difference in thermal stability of the two compounds is due to the stronger polarization action of Mg + than that of Ca upon the 0 ion. 

S5nnmetrical polarization appears as a particular case of asymmetrical polarization (for the case previously discussed, toward an anion is exercised equal polarizing actions, from opposite directions). 

The counter-polarizing action of bivalent cations of small radius is noted also in the lattices of sulphates, nitrates, orthosilicates, etc. in terms of reduction of thermal stability (the decrease of decomposition or melting temperature). 

The strong polarization of I respecting Cd determines the shortenes of the Cd - I distances while keeping the symmetry of polyhedron CdIg. The counter-polarizing action of another cadmium ion should ensure the symmetry for the polyhedron ICdj since a single kind of cations of the lattice. 

The fact that both reactions are catalyzed by the polarizing action of an acid-base pair emphasizes this property as the main characterization feature. The reaction will not be probing properties such as the ability to abstract protons from reacting molecules [235]. The probe reaction also exemplifies that catalysis is seldom an action of a single monofunctional site, but requires a multitude (of sites) to facilitate the complex rearrangement of bonds during reactions. 

We studied solubilities of 11 oxides in this melt at 700°C and developed the methods of saturation detection to determine in some cases dissociation constants. - The dependence of pKj index in molar fractions (pK x, Meo) vs. polarizing action of cation by Goldschmidt for all cations (excluding Pb atKl Cu2 ) can be expressed by the following eqiration ... 

Figure 9.2.8. The dependences of pK vs. polarizing action of the corresponding cation hy Goldschmidt (Z e r the data obtained by different investigators 1 - Tremillon et a , 54,5s,i5i,2i5.2i8 2 Delimarsky...

The dependence of pK polarizing action of cation by Goldschmidt is as follows ... 

The data collected in this table show that the order of arrangement of oxides according to increase of their solubility corresponds to the similar dependences in the KCl-NaCl and CsCl-KCl-NaCl melts at 600 and 700°C. The performed study makes it possible to estimate the dissociation constants of PbO and CdO, which are close, therefore, it can assumed that the dissociation constants of oxides, having close solubility product values, are practically the same. The solubility parameters are close to those in the KCl-NaCl melt at 700°C. The dependences of the oxide solubility on the polarizing action of cation by Goldschmidt can be approximated by the following equation ... 

On platinum black in 50% ethanol at 25°C the reduction process is controlled by activation of the other reactant (nitrobenzene). In this case there is a linear relationship between the logarithms of the reduction rate constants for the nitrobenzene derivatives and the corresponding Hammett substituent constants, where the electron-acceptor substituents accelerate the reduction and electron-donor substituents retard it. A similar relationship was obtained between the rate of the process and the polarizing action of electron-donor substituents on skeletal nickel alloyed with titanium when the nitro compounds were... 

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