Anion polarizable

A leading factor that influences the potentials is the presence of anionic (polarizable) ligands. The potentials are lowered in the following series ArO- > ArS- > RS-.298... 

I think that we do not understand specificity very well. We should remember the importance of anion polarizability and we should not lose sight of peculiar cases such as the precipitation of potassium tetraphenyl borate, K+(Bcf>4). ... 

Again we digress to discuss soft and hard (11). It has been said that polarizability measures softness and that the permanent charge-cloud distortion is responsible for (b)-class behaviour. Unfortunately polarization energies of this kind work in two ways — they generate (i) (b)-class behaviour due to anion polarizability but (ii) (a)-class behaviour due to the cation polarizability. Thus if softness and polarizability are related they are not necessarily related to (b)-class behaviour. Moreover on the basis of polarizability of this kind there can be no preferential soft-soft or hard-hard interaction. 

In the molecular dynamics approaches to such systems, one of the principal novelties compared with the work on simpler systems such as KCI (Section 5.3.3) is the taking into account of anion polarizability, i.e., elimination of the hard-sphere approximation. Anions are by and large more polarizable than cations. The polarizability ce is proportional to rf. The radii of cations, formed by losing an outer electron, are smaller than those of the anions, which are formed by adding an electron. Hence, anions are mainly the ions affected when polarizability is to be accounted for. 

Calculations taking into account the anion polarizability in AICI4 reduce the approximation associated with the simple additivity of pairwise potentiais in computational modeling (hard-sphere approximation) of molten salts. They predict new entities (e.g., AljClg) and in this respect have an advantage over earlier calculations. 

Although molecular polarizabilities are known with precision, the apportionment between cation and anion polarizabilities is a difficult problem. This situation is analogous to the apportionment of cation and anion crystal radii. Roberts arbitrarily assumed q d(0 ) = 2.387 A whereas Lasaga and Cygan " did not specify the source of their value of 2.37 A. ... 

The stmctural preference within the series of trifluorides is dominated by the nature of the M F covalent interaction. As we move to the heavier halides, that is, as the anion polarizability increases, lower dimensional stmctines become prevalent. For these materials, three major interatomic... 

Simple Anionic Adsorption from Solution. - Here the relevant equation would be (11), and again the equilibrium would be pH dependent but in this case shifts to the left at a high pH. It is also dependent upon the ionic affinity which increases with anionic polarizability and ionic charge, e.g., I" > Br > Cr > F- and SOf > Q". 

Dorenbos P, Andriessen J, van Eijk CWE (2003) 4f" 5d centroid shift in lanthanides and relation with anion polarizability, covalency, and cation electronegativity. J Solid State Chem 171 133... 

Phosphates and phosphorothioates are insensitive to anion polarizability in this reaction. 2-Pyridone is a better nucleophile than 2-pyridinethione (relative rates = 28 1). The rates of these reactions have been correlated with acidities for several carboxylic acids, phenols, and thiophenols. ... 

Jemmer P, Fowler PW, Wilson M, Madden PA (1998) Environmenteil effects on anion polarizability Variation with lattice parameter tmd coordination number. J Phys Chem A 102 8377-8385... 

Atomistic Simulation. The simplest models of surfaces are based on an ionic model in which the structure of the surface is largely controlled by electrostatic considerations. In these cases, the electrostatic interaction between ions can be modeled using periodic adaptations of the Coulombic sum, usually the Ewald sum for the 3D periodic slab calculations and its 2D adaptations for dedicated surface simulation codes such as METADISE (397) and MARVIN (398). The inclusion of anion polarizability via the shell model is easily incorporated into these calculations since the shell can be treated as an additional interaction center and its interaction with its own core subtracted after the periodic sum has been carried out. 

Stuart and Berne [62] have compared the effective two-body TIP4P and a polarizable version based on a fluctuating charge model TIP4P-FQ to solvate either a non-polarizable or a polarizable chloride ion in clusters (H20)nCl for n up to 255. The polarizability model of the ion is based on a Drude oscillator representation. Their simiflations have shown that the chloride ion is solvated at the surface of the cluster for the polarizable model, but the ion is solvated inside the cluster for n < 18 for the non-polarizable model. The explanation for this behaviour is mainly the stronger dipole moment that can be created on water molecules with the polarizable model. Chloride anion polarizability has not been found to have an important effect on the structure of the clusters. 

The equilibrium distances di and 2 are obtained by minimization of the total energy. In order to display more clearly the rumplmg effect, it is convenient to introduce the parameters d and 5 (di = d + 5 and 2 = d — )- In the absence f anion polarizability (a = 0), the rumpling amplitude 28 vanishes and d has the value already obtained in the study of relaxation effects (Section 2.3). The two first terms in the expansion of the total energy with respect to 8 are of zeroth and second order ... 

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