Interactions inter ionic

Higher melt temperatures lead to an increase in band intensity and merging thereof, as shown in Fig. 84. The merging of bands that occurs at increased temperatures can be explained by the augmentation of ion diffusion that causes an averaging of the potential of inter-ionic interactions between the NbF6 ions and the outer-sphere cations. 

The main problems encountered in the investigation of tantalum- and niobium-containing fluoride and oxyfluoride complexes are related to the tendency of the compounds to undergo hydrolysis, particularly at elevated/high temperatures. In addition, the interpretations of the observed effects are often nontrivial and unclear due to the relatively complicated inter-particular interactions and changes that occur under thermal treatment. From this point of view, vibration spectroscopy methods are of high importance due to the dependence of solid phase spectra on the temperature, which, above all, stems from the nature of such inter-ionic interactions [369]. 

It is obvious that calculated values are systematically lower than the experimental data. Comparison of the experimental and calculated values of coefficient p shows that along with the changes in occupancy levels that appear at elevated temperatures, inter-particular interactions also make a significant contribution. Band intensity is generally defined as the derivative of the dipole moment with respect to the normal coordinate. It is, therefore, logical to assume that thermal extension and outer-sphere cation replacement have a similar influence on the potential of inter-ionic interactions, which, in turn, lead to the intensity changes. 

Based on the classical Dexter-Forster model of inter-ionic interaction induced energy transfer, the excitation probability of ion i can be expressed as (Dexter, 1953 Forster, 1948 ... 

The first accurate calculation of the activity coefficient based on energetic effects of inter-ionic interactions in solvents was carried out by -> Debye and -> Huckel in 1923 by assuming that all the deviations from ideality at low concentrations of electrolyte were due to interionic interactions (- Debye-Huckel theory) with this it is possible to show that... 

We consider first the low-concentration branch, where the WP decreases rapidly with increasing molar concentration c of the salt. In contrast to the situation encountered for aqueous systems, in low-e solvents one does not reach the limiting regime of the Kohlrausch-Debye-Hiickel-Onsager c1/2 law [40], which results from long-range inter-ionic interactions between free ions. Even at the lowest concentrations a controls the concentration dependence of the WP, thus enabling the determination of the association constant K (T) for ion pair formation. 

A variety of publications are dealing with T1 relaxation measurements in combination with NOE experiments to investigate the reorientational dynamics of ionic liquids in solution (and sometimes also in the solid state) [17-22], The data can then be interpreted concerning inter-ionic interactions and phase transitions. 

Among the thiocyanates another order-disorder phase transition is possible. This involves a transition from an ordered structure similar to potassium thiocyanate to a disordered structure isostructural with potassium cyanate. This has been observed in potassium thiocyanate at 145 °C but has not been observed up to 300 °C in the nearly isostructural sodium salt. Iqbd (41) has suggested an explanation for this behaviour in terms of the greater anisotropy of the inter-ionic interaction potential in potassium thiocyanate compared with the sodium salt. 

These two experiments coupled with ordinary conductance and activity coefficient studies demonstrate conclusively the correctness of the basic posmlate of the Debye-Hiickel theory, that is, the existence of the ionic atmosphere which is itself a manifestation of the inter-ionic interactions occurring in electrolyte solutions. They also suggest that the main properties of the ionic atmosphere which must be taken into consideration in developing a theory of conductance are ... 

Crystal structure of [CoCp2][Tp MoOS(OC6H4C02Et-2)] showing (a) ORTEP projection of anion and (b) inter-ionic interactions stabilizing and ordering the oxo and sulfido ligands. Part (b) adapted with permission from ref. 270. Copyright (2015) American Chemical Society. 

---