Polar bonding ionicity parameter

Using the separation of the effective Hamiltonian into the unperturbed part and the perturbation, the total ionic contribution to the geminal is calculated exactly (vari-ationally). Only the bond polarity needs to be estimated perturbatively in the linear response approximation, but now the correlated ground state of the symmetric effective bond Hamiltonian is taken for evaluating the response function. In this context, it is convenient to use a dimensionless bond asymmetry parameter ... 

Difficulties in the accurate calculation of bond ionicity and radii of atoms in polar bonds do not permit to predict the parameters of polymorphic transformations by the crystal-chemical method, but a global physical theory does not yet exist. This led to the development of the statistical approach, to structural maps with various coordinates, such as an electronegativity (x), atomic radius (r), the number of valence electrons, etc. Thus, various structure types were plotted in 2D-maps with the coordinates n - Ax, where h is the mean principal quantum number (Fig. 9.3) [10-12] Burdett et al. [13] used as coordinates the Coulombic (C) and homo-polar (Eh)... 

So the kinetic scheme and parameters not only depend on M, but they may differ considerably according to the initiator used. Furthermore, the active centers are not uniform as in free-radical polymerization, but because of their ionic nature there usually exists a complex chemical equilibrium between different species, even if the initiator has a unique stmcture. This equilibrium [Eq. (3)] between free ions, solvent-separated ion pairs, contact ion pairs, covalent polarized bonds, and between associated and non-associated species, as well as the concentration of these species strongly depend on the polarity or solvating power of the solvent system, the solvent itself, and the presence of other salts. 

The squared polarization coefficients (given as parenthesized percentages before each hybrid listing) indicate that the <7hf bond is rather strongly polarized toward F (77.68% on F, 22.32% on H), with corresponding ionicity parameter [cf. (4.18)]... 

For ionic (Li+F ) NBO structure. The (af parameter is obtained from a corresponding CHOOSE structure with highly polarized Li—F bond. 

An anion effect is also reported for the solid-state anations of cis-[Co(en)2(py)X]Y2 (X- = Cl-or Br- Y- = Br" or I"). Experimental conditions affect activation parameters, and the kinetic compensation effect is observed (that is, a is linearly correlated with log A). However, the correlation is different for [Co(en)2(py)X]Br2 than for [Co(en)2(py)X]I2.71 This result suggests that the chemical process of importance is anion-dependent. It is proposed that the Co—py bond strength is affected by polarization effects due to the surrounding ionic halides. 

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