Weaker hydration structure

If organic solvents such as ketones or alcohols are added in considerable amounts, the redox potential is shifted towards more negative values (22) since, owing to the breakdown of the outer-sphere hydration, the stabilizing effect of water is no longer available (alcohols are known to have considerably weaker EPA properties). The outer-sphere hydration structure is more readily destroyed by the increasing donicity of the solvent that replaces water in the mixture. The destructive effect is more pronounced with the reduced species than with the oxidized one since the latter is less stabilized by hydration, and the redox potentials thus become more negative. 

The ion-water interactions are very strong Coulomb forces. As the hydrated ion approaches the solution/metal interface, the ion could be adsorbed on the metal surface. This adsorption may be accompanied by a partial loss of coordination shell water molecules, or the ion could keep its coordination shell upon adsorption. The behavior will be determined by the competition between the ion-water interactions and the ion-metal interactions. In some cases, a partial eharge transfer between the ion and the metal results in a strong bond, and we term this process chemisorption, in contrast to physisorption, which is much weaker and does not result in substantial modification of the ion s electronic structure. In some cases, one of the coordination shell molecules may be an adsorbed water molecule. hi this case, the ion does not lose part of the coordination shell, but some reorganization of the coordination shell molecules may occur in order to satisfy the constraint imposed by the metal surface, especially when it is charged. 

The partially hydrogen-bonded structures can best be classified in two groups, according as to whether the hydrogen bonds form a weaker element in an otherwise rigidly determined structure, as in the case with most hydrated ionic salts, or, on the contrary, whether the hydrogen bonds form the strongest elements in a structure otherwise determined by weaker van der Waals or dispersion forces, as in most molecular crystals. 

The 1-substituted 1,2,4-triazole 4-oxides with the basic structure 532 are hygroscopic. They form hydrates, which lose the water by heating to melting or by recrystallization from anhydrous solvents. 1,2,4-Triazole 4-oxides 534 are 4 p/< , units weaker as a base than their deoxygenated progenitor 533 (1972JPR101). 

Anions have a much weaker tendency to coordinate water molecules than cations and precise values for hydration numbers are difficult to obtain from X-ray data. Although a hydration sphere around an anion is often included in the least-squares analysis of an intensity curve for a metal salt solution, meaningful values are usually obtained only for the bond lengths. Coordination numbers and rms variations are often kept constant at assumed values. For the halide ions the bond lengths found show no significant deviations from values in crystal structures. 

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