Hydration shell trivalent ions

Polyvalent metals. Protons can be liberated by hydrolysis of hydrated polyvalent metals such as Al, Fe(II), and Fe(III). Aluminum ions in the weathering environment are coordinated with six molecules of water (Jackson, 1963) the water in this hydration shell is more acidic than bulk water (Stumm and Morgan, 1981). Trivalent hexa-hydronium Al ion, by reacting with water, liberates protons and acts as an acid (Jackson, 1960, 1963) as shown in the following reaction ... 

The strongly hexahydrated trivalent ions may have a stronger second hydration shell than mono-and divalent ions. Many authors have adopted structural models with 12 water molecules in the second hydration shell of the trivalent ions. However, the tilt angle of water moleeules in the first hydration shell of Cr " " and Fe ions is in favor of the eonstmetion of three hydrogen bonds with water molecules in the second hydration shell. Thus, for the evaluation of orientation of water molecules and the mo(2) value more detailed investigations may be needed. The rMO(2) values... 

Then the solvent-coordination number of the ion in the solution, h, is obtained by the integration according to Equation 4.32. Second hydration shells have been definitely ascribed to divalent and trivalent cations from x-ray diffraction measurements. The coordination number h for water molecules in this second shell is generally assumed to be 12, the number then being corroborated by the diffraction data. 

Mochizuki and Okamoto applied the Dirac program for the estimation of stabilities of trivalent actinide elements and water or ammine complexes (Mochizuki and Okamoto 2002). Mochizuki and Tatewaki (2002) also carried out the electronic structure calculation on the hexa-hydrated ions of curium and gadolinium. They used the Dirac program and also predicted the fluorescence transition energy using the Complete Open-Shell Configuration Interaction (COSCI) method. Even the hexa-hydrate curium ion needs 2,108 basis functions for the fully relativistic four-component calculation. 

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