Inner and outer coordination sphere

It is well known, that in aqueous solutions the water molecules, which are in the inner coordination sphere of the complex, quench the lanthanide (Ln) luminescence in result of vibrations of the OH-groups (OH-oscillators). The use of D O instead of H O, the freezing of solution as well as the introduction of a second ligand to obtain a mixed-ligand complex leads to either partial or complete elimination of the H O influence. The same effect may be achieved by water molecules replacement from the inner and outer coordination sphere at the addition of organic solvents or when the molecule of Ln complex is introduced into the micelle of the surfactant. 

AG and AG 0 are the inner and outer coordination sphere contributions, as in the homogeneous case, and AG the free energy contribution due to electronic multiplicity, usually zero. 

The very precipitate changes in ASX and AHT which occur over very small changes in apparent radius arises from the cooperative interaction within the inner and outer coordination spheres involving large numbers of molecules. This means that electrostatic interactions have considerable selectivity in overall structure hidden behind very small differences in AG. Since in biology structure and motion within structure are as important as stability we shall need to keep this feature in mind. 

Ionization isomerism is best characteized in systems involving substitutionally inert metal ions where kinetic, rather than thermodynamic, factors control isomer formation. Numerous cases are known of cobalt(III) compounds in which exchange of a ligand between inner and outer coordination spheres results in a spectacular colour change. Thus, tra/is-[CoCl2(en)2]N02 (en = 1,2-ethanediamine) is green and frans-[CoCl(N02)(en)2]Cl is orange tmns-[CoCl(NCS)-(en)2]NCS is blue and frans-[Co(NCS)2(en)2]Cl is deep red. 

Circles represent inner and outer coordination spheres. Abbreviations M q, hydrated metal ion M, metal and L, ligand. 

Subscript and superscript Ln have been added to avoid confusion with the other definition of quantum yield discussed below. The quantity defined in (16) is called the intrinsic quantum yield, that is, the quantum yield of the metal-centered luminescence upon direct excitation into the 4f levels. Its value reflects the extent of nomadiative deactivation processes occurring both in the inner- and outer-coordination spheres of the metal ion. The rate constant A obs is the sum of the rates of the various deactivation processes ... 

The Coulombic interaction term AG can be calculated using Debye-Hiickel theory or can be neglected if the ionic strength and the dielectric constant of a solution are high and large reactant ions are used.X has the dimensions of energy and is a measure of the reorganization of the inner- and outer coordination sphere, necessary to reach the transition state its value is times the acti-... 

I mechanisms, or concerted mechanisms, are the interchanges of ligands X and Y between inner and outer coordination spheres of the metal. These mechanisms can involve different transition states, where I and I3 are extreme (border) cases. 

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