Charge, metal coordination number effects

Channels, supramolecular complexes, 46 222-227, 283-289, 291-292 Charge, metal(I) coordination number effects, 37 38-39... 

Extractive separation of metals is usually based on complex formation with inorganic and organic ligands. Therefore the use of the ideas, approaches, and methods of coordination chemistry has always been a most fruitful approach to the extraction of the elements. History shows that many problems of selectivity of separation or enhanced isolation have been successively solved by the rational application of coordination chemistry, e.g., the concept of hard and soft acids and bases. The efficiency of extraction depends on, inter alia, the ratio of charge and coordination number of metal ion. Study of this effect permitted the development of ways to improve separation due to changes in hydration of the species to be extracted. 

The precise nature of the complex depends on the charge, z, coordination number, N, and electronegativity, Xm> of the metal and the pH of the aqueous solution [8]. It is also necessary to consider the possible effects of ligand field stabilization which are most important for d and t/ ions [10]. The typical effects of charge and pH are shown schematically in Fig. I, where three domains corresponding to aquo, hydroxo, and oxo ions are defined [11,12]. This diagram explains in a qualitative manner why the hydrolysis of low-valent cations (z < 4) yields aquo, hydroxo, or aquo-hydroxo complexes... 

Effect of protonation, complex formation with ligands and metal ions and reduction on dissolution rate. The structures given here are schematic short hand notations to illustrate the principal features (they do not reveal the structural properties nor the coordination numbers of the oxides under consideration charges given are relative). 

When simply hydrated, the number of water molecules bonded to the metal (central) ion correspond to a value N, the coordination number, which is also termed the hydration number. In complexation, ligands displace the hydrate waters, although not necessarily on a 1 1 basis. Charge, steric, and other effects may cause the maximum number of ligands to be less than N. For example, in... 

Even in the absence of a free electron gas that causes charge redistribution at low coordination number sites on metal surfaces there are strong chemical effects associated with atoms in surface irregularities. The rehybridization of localized electron orbitals should have a marked effect on the chemical... 

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