Coordination spheres definition

The definition of solvent exchange rates has sometimes led to misunderstandings in the literature. In this review kjs 1 (or fc2lsolvent]), sometimes also referred to as keJ s 1, is the rate constant for the exchange of a particular coordinated solvent molecule in the first coordination sphere (for example, solvent molecule number 2, if the solvent molecules are numbered from 1 to n, where n is the coordination number for the solvated metal ion, [MS ]m+). Thus, the equation for solvent exchange may be written ... 

By definition, the coordination number includes the adjacent atoms, and lone electron pairs are not counted. On the other hand, now we are considering lone pairs as occupying polyhedron vertices. To take account of this, we regard the coordination sphere as including the lone pairs, but we designate them with a //, for example -octahedral = octahedron with two lone electron pairs and four ligands. 

From the viewpoint of coordination chemistry, a substitution reaction can be defined as a process whereby a ligand in a complex is replaced by another ligand from outside the coordination sphere [1], Substitution reactions by metal complexes have been classified by Saito [2] according to Taube s definition [3] of inertness. Saito classified metal ions into three groups as follows ... 

In aqueous solutions, however, the complexes are usually present in compositions in which water molecules complete the coordination sphere of the metal up to a definite number, usually 2, 4, or 6. Thus, the complexes are formed as represented by the equations... 

In the end, while computations on these alternative pathways, oxidative addition and cr-bond metathesis, have provided some insight, the question by which way does a particular reaction proceed cannot yet be answered definitively. It is very interesting, however, that both mechanisms involve the same Pt(II) intermediate in which the hydrocarbon binds in the square-planar coordination sphere of the metal. 

If there is no pathway independent of the chloride, that is, if extrapolation to very low chloride concentration of chloride exchange reaction led to a zero intercept and no free ion pathway, then we would have a bimolecular reaction. This definition of bimolecularity only requires chloride to be a component of the second coordination sphere for chloride exchange to occur. 

Figure 1 depicts schematically the interaction of solvated ions with the electrode surface both for outer sphere (a) and inner sphere pathways (b). Notice, however, that some ambiguity is found with respect to the previous definitions for case (c) in which the coordination sphere of the reacting ion penetrates the layer of solvent molecules adjacent to the electrode, but the ligand is the same solvent molecule and therefore cannot be distinguished from the inner layer of solvent molecules. This may be considered an outer sphere pathway unless the solvent ligand adjacent to the electrode is not present in the product of reaction. 

One can define diastereoselectivity as the formation of diastereoisomers in a non-statistical ratio in any chemical transformation (formation of transition states included). Such a definition concerns equilibrium as well as nonreversible reactions. An asymmetric synthesis in a restricted sense can be considered as a reaction leading to a product containing at least one new stable dissymmetric center with a definite chirality. Such a reaction may take place in the coordination sphere of a metal ion. First of all the following question has to be answered which are the structural properties in the architecture of the coordination sphere that lead to the following phenomenona ... 

The "non-classic structure of 7r-allylic complexes means that a substituted 7r-allylic group could exist in two isomer forms (syn and anti). The formation of definite structure depends on the nature of ligands in the inner coordination sphere of the central atom. 

Thus, from the above results and from those concerning the propagation rate constant values, it may be concluded that the support becomes part of the catalyst system. The presence of Mg ions in the second coordination sphere of Ti ions results in a definite modification of the active center reactivity. Unfortunately, no comparable... 

This masking of the typical ligand reactivity via coordination is a thread which runs throughout early work on these compounds and allowed the concept of the coordination sphere to be put on a definite basis as a result of chemical tests. 

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