Water molecule, displacement

Metal ions dissolved in water are effectively complexed to water molecules. Displacing the set of water ligands, partially or entirely by another set, in such aqua metal ions results in... 

Alcohols are hydroxylated alkyl-compounds (R-OH) which are neutral in reaction due to their unionizable (OH) group (e.g., methanol, ethanol, isopropanol, and w-butanol). The hydroxyl of alcohols can displace water molecules in the primary hydration shell of cations adsorbed onto soil-solid and sediment-solid clay particles. The water molecule displacement depends mainly on the polarizing power of the cation. The other adsorption mechanisms of alcohol hydroxyl groups are through hydrogen bonding and cation-dipole interactions [19,65],... 

Stability constants are calculated from the concentrations of the species present in equilibrium mixtures containing the metal ion and the ligand in a wide range of proportions. Activity coefficients are kept constant by appropriate additions of a salt, usually sodium perchlorate, whose ions do not compete with those of the cation and ligand. Concentrations at different ionic strengths are extrapolated to zero ionic strength. It may be necessary to find the number of water molecules displaced at each step the total of these is not necessarily the same as the co-ordination number of the cation in the solid compound. Particularly in a polar solvent such as water, the ligands may not displace all the solvent molecules. 

In both cases, the cobalt containing product is the aqua complex because H2O is present in abundance, and high-spin d complexes of Co(II) are substitution labile. However, something that distinguishes the two pathways is the composition of the vanadium-containing product. If [V(N3)(OH2)s] is the product, then the reaction has proceeded via an inner-sphere pathway. If [V(OH2)6] " is the product, then the electron-transfer reaction is outer-sphere. The complex [V(N3)(OH2)5] is inert enough to be experimentally observed before the water molecule displaces the azide anion to give [V(OH2)6]. ... 

The thermodynamic stability constant k which represents the free energy of complex formation (AF° = — RT In k ) can be subdivided into heat and entropy terms (AF° = AH° — TAS°). The entropy of complex formation has been discussed elsewhere (Cobble, 1953 Schwarzenbach, 1954 Williams, 1954). The factors involved include (1) the size and geometry of metal ions and ligand molecules 2) the change in the number of molecules in the system on complex formation as they affect translational freedom (3) restrictions on the freedom of rings imposed by chelation and other restrictions of internal rotation and (4) the entropy of hydration for the water molecules displaced by ligands. 

Whereas, if dispersion interactions between ions on the surface are important, then a term in 0 becomes significant. The form of (0) is normally taken as 0/(1 - Qf where p is the number of water molecules displaced by one adsorbed ion. Details of the various isotherms are given elsewhere [28], but modem simulation methods, as reviewed below, are needed to make further progress. 

To include an adsorbed species, one or more surface water molecules are removed and the adsorbate added. Figure 3.7(c) illustrates the adsorption structure of sulfate at a fully solvated electrode surface with one water molecule displaced. The choice of cell size, adsorbate site (which also sets position within the water layer), water density, and water structure can all affect the computed results. As these choices can only be loosely based on matching an actual system, and testing of the impact of all of them is often intractable, choices should be made consistently between reactants and products to take advantage of cancellation of variability. For the anion adsorption reaction [eqn (3.7)], adsorption occurs with displacement of some number of water molecules ... 

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