Reactions Involving the Coordination Shell

What may be apparent from this very brief overview is that the Periodic Table location of metals plays a strong role in determining their coordination chemistry - to the point that each has truly unique coordination chemistry. However, certain global traits exist to guide the synthetic chemist. The above notes may serve to support the following specific discussion of synthetic methods. 

As an example, consider reaction (6.1). Here, the Cu2+aq ion has water ligands in its coordination sphere substituted by a stronger ligand, in this case ammonia, to form [Cu(NH3)4]2+. Multiple ligand substitution is assisted by the use of an excess of the incoming ligand to drive equilibria towards the fully-substituted compound. 

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Rather, the reactions will be interpreted as reverse aldol and then aldol reactions within the coordination shell of a metal, involving the transient existence of a metal complex of a cw-enediol and a hydroxyaldehyde (Figure 6.2). The isomerisation occurs when the carbonyl moves over the face of the enediol and recombines with the other carbon. The carbonyl group is a poor ligand and can thus break free of the complex simple rotation about C3-C4 while still attached to the metal will yield side-products epimeiised at C3. If the hydroxyaldehyde it is not held to the metal by other hydroxyls, particularly 04, it can escape completely. 

The key to the outer sphere mechanism is that electron transfer from reductant to oxidant occurs with the coordination shells (or spheres) of each reactant staying intact throughout. Since the coordination (or inner) sphere, that is the set of bound ligands, is not changed during the reactions, it appears that the key to the process lies beyond these, in the outer sphere around the reactants. We have seen an example earlier involving two different metal centres. Another classical example of pure electron transfer alone, involving two oxidation states of the one metal ion, is Equation (5.54). 

The majority of complexes are prepared through reactions involving ligand substitution in the coordination shell. 

Sorption and desorption are chemical reactions by which certain metals (e.g., Fe, Cu, Zn, and Mn) and anions (e.g., phosphate and sulfate) form/break chemical bonds within the coordination shell of atoms comprising the mineral structure. Sorption includes both adsorption and absorption. Physical adsorption refers to the attraction caused by the surface tension of a solid that causes molecules to be held at the surface of the solid. This type can also be reversible. Chemical adsorption (not reversible) involves actual chemical bonding at the solid s surface. Absorption is a process in which the molecules or atoms of one phase penetrate those of another phase. 

As is seen from discussion above, the vast majority of Mizoroki-Heck reactions belong to either type 1 or type 2 processes, which involve palladium with undefined coordination shells. In the presence of halide ions (liberated during the reaction or derived from additives) and anionic bases, the coordination shell of palladium contains as many anionic ligands as it can pos sibly bear [32]. Thus, these catalyses do only pass through coordination equilibria involving charged reactants on both sides. Similar considerations apply to typed systems, which involve cationic intermediates. 

By virtue of the high donor number of the solvent ligand exchange reactions involving replacement of solvent molecules in the coordination shell by weak competitive ligands are unlikely. Manganese(II) bromide is ionized and no... 

If the charge transfer step of a redox process (such as Equation 1.106) is rate determining, the Butler-Volmer equation is obtained as follows. A similar equation is obtained for metal dissolution where the concentrations c(Ox) and c(Red) are replaced by c(Me +) and G g. As usual in chemical kinetics, the rate constants k contain an exponential term with the ratio of the standard activation free enthalpy A,G to RT. A,Gt is the barrier that the reacting system has to overcome to get to the transition state from which the products are formed. For a simple redox reaction, this involves the change of the coordination shell of solvent molecules and other ligands, i.e., for (Fe(CN)6) " . 

We recall that outer-sphere reactions involve the outer coordination sphere of reacting ions thus, little if any change occurs inside the ion solvate shell. These reactions proceed without breaking up intramolecular bonds, whereas in inner-sphere reactions, involving the inner coordination sphere, the electron transfer is accompanied by the breaking up or formation of such bonds. Inner-sphere reactions are often complicated by the adsorption of reactants and/or reaction products on the electrode surface. 

The most important single development in the understanding of the mechanisms of redox reactions has probably been the recognition and establishment of outer-sphere and inner-sphere processes. Outer-sphere electron transfer involves intact (although not completely undisturbed) coordination shells of the reactants. In inner-sphere redox reactions, there are marked changes in the coordination spheres of the reactants in the formation of the activated complex. 

A systematic ab initio investigation of the water-assisted decomposition of chloro-methanol, dichloromethanol, and formyl chloride as a function of the number of water molecules (up to six) building up the solvation shell has been reported.33 The decomposition reactions of the chlorinated methanols and formyl chloride are accelerated substantially as the reaction system involves additional explicit coordination of water molecules. 

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