Generalizations for Intermolecular Interactions

Generalization 1 AeL Aey- The destabilization of the upper MO relative to the higher energy interacting orbital is approximately the same as the stabilization of the lower MO relative to the lower energy interacting orbital. 

Generalization 3 ( - eL ) AeL j . The magnitude of the difference between destabilization and stabilization is small compared to the actual magnitudes of the stabilization and destabilization. 

Generalization 4 hAB k(eA + eB)SAB (k a Positive Constant, SAb Assumed Positive). The interaction matrix element is not precisely proportional to the overlap integral but the behavior with respect to distance and symmetry is essentially the same. In other words, hab will be zero by symmetry when Sab is zero by symmetry, but not otherwise. Also, hab decreases in magnitude as a function of increasing separation in much the same way as S. Thus, two orbitals will not interact if they behave differently toward local elements of symmetry. 

The proportionality to the sum of unperturbed orbital energies [see also equation (3.44)] may be misleading. Large negative values for orbital energies are associated with core orbitals for which the overlap is close to zero. 

The proportionality to the sum of unperturbed orbital energies [see also equation 

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The cooperative mechanism of the spin-crossover phenomenon is well imderstood in some aspects. For instance, theoretical models account for the thermal evolution of the system. However, due to their phenomenologic character, the key parameters accounting for intermolecular interactions do not reflect the relevance of the microscopic details which could orientate us in designing molecules that can recognize each other and combine to produce systems with prescribed characteristics. Consequently, very general principles guide the syntiietic chemistry in the search for suitable spin-crossover compounds often trial and error or serendipity are the sole strategies. 

The difference between solid solubilities in a given SCF depends mainly on the solid vapor pressure and intermolecular interactions between the solvent and solute. The individual solubilities of solids can vary greatly although most values are well below 10 mol%. The differences between enhancement factors are less pronounced [14,15], however, which suggests that the vapor pressure of the solid exerts the primary influence on solubility. Intermolecular interactions between the solvent and solute depend on the types of functional groups present in their chemical structures. In general, the intermolecular interactions are dominated by dispersion forces, which accounts for the similar values of the enhancement factor for many solids. 

Theoretically, these intermolecular interactions could provide adhesion energy in the order of mJ/m. This should be sufficient to provide adhesion between the adhesive and the substrate. However, the energy of adhesion required in many applications is in the order of kJ/m. Therefore, the intermolecular forces across the interface are not enough to sustain a high stress under severe environmental conditions. It is generally accepted that chemisorption plays a significant role and thus, physisorption and chemisorption mechanisms of adhesion both account for bond strength. 

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