Intermolecular interactions, viii

Comparison of the tetramethyldipnictogens with the isoelectronic dihalogens is particularly informative. Cl2, Br2, and I2 crystallize in isostructural molecular lattices with increasing intermolecular interaction (54,59). For iodine, the atoms are connected intramolecularly at 2.72 A and inter-molecularly in a two-dimensional rectangular net at 3.50 and 3.97 A. The ratio E—E/E—E drops from 1.68 for Cl2 to 1.29 for I2. Only for I2 is there an appreciable intermolecular interaction. Again the brake occurs between the fourth and fifth periods of elements (see Table VIII) (54,59). The... 

The first chapter by Moszyliski presents in a systematic and comprehensive manner the current state-of-the-art theory of intermolecular interactions. Numerous examples illustrate how theoreticians and experimentalists working in tandem may gather valuable quantitative results related to intermolecular interactions, like accurate potential functions, interaction-induced properties, spectra and collisional characteristics or dielectric, refractive or thermodynamic properties of bulk phases. On the other hand the most advanced Symmetry Adapted Perturbation Theory (SAPT) enables validation of more approximate variation-pertubation models which could be applied to the analysis of specific interactions in much larger molecular systems, for example enzyme-drug interactions discussed in Chapter VIII by Berlicki et al. 

The laws governing the interfacial phenomena between condensed phases and their vapor (or air) in single- and two-component systems, described in previous chapters, are largely applicable to the interfaces between two condensed phases, i.e., between two liquids, two solids, or between a solid and a liquid. At the same time, these interfaces have some important peculiarities, primarily related to the partial compensation of the intermolecular interactions. The degree of saturation of the surface forces is determined by the similarity in the molecular nature of the phases in contact. When adsorption of surfactants takes place at such interfaces, it may substantially enhance the decrease in the interfacial energy. The latter is of great importance, since surfactants play a major role in the formation and degradation of disperse systems (see Chapters IV, VI-VIII). 

Table VIII lists some of the more important physical properties of TeF4. In the orthorhombic crystals, each tellurium atom is surrounded by three terminal and two bridging fluorine atoms, arranged at the apices of a distorted square pyramid. The square-pyramidal units are linked by cis-bridging atoms into endless chains with a bridge angle of 159°. The nearest intermolecular contacts to the tellurium atom are 2.94 and 3.10 A, so that there are no other significant interactions. This geometry is in accordance with the steric activity of the lone electron pair at the tellurium atom. Figure 6 shows the atomic arrangement (54).

It may thus be concluded that variations in Kd can to a large extent be rationalized in terms of charge effects, but that intramolecular hydrogen bond interactions (a type) may contribute significantly to stabilization of the dinuclear species. Intermolecular hydrogen bond interactions may stabilize the mononuclear species, but in the case of +2 charged cations such interactions are measurable only in very concentrated solutions. The possible kinetic consequences of these inter- and intramolecular hydrogen bond interactions are discussed in Sections VII and VIII. 

It has been concluded that the interaction of an analogous vanadium complex with hydrocarbons does not occur by a simple ct bond metathesis mechanism [35b], The alkylidene tantalum(V) complexes undergo intermolecular cyclo-metalation of the aryloxide hgand [35c] (Scheme VIII.5). 

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