Secondary Coordination Sphere

The complex in which olefin is bound by the donor acceptor bond to the oxygen atom of hydroperoxide and exists in the secondary coordination sphere is also considered in the literature [241]. 

As with any metalloprotein, the chemical and physical properties of the metal ion in cytochromes are determined by the both the primary and secondary coordination spheres (58-60). The primary coordination sphere has two components, the heme macrocycle and the axial ligands, which directly affect the bound metal ion. The pyrrole nitrogen donors of the heme macrocycle that are influenced by the substitutents on the heme periphery establish the base heme properties. These properties are directly modulated by the number and type of axial ligands derived from the protein amino acids. Typical heme proteins utilize histidine, methionine, tyrosinate, and cysteinate ligands to affect five or six coordination at the metal center. 

The ligands of a lone-pair cation lie on the surface of a sphere. When TU is surrounded by weakly bonding oxyanions, it lies at the centre of the sphere, forming nine bonds of 297 pm each (O.llvu, Fig. 8.2(a)). When it bonds to strongly bonding anions, as in TI3BO3, TU moves about 70 pm away from its centre to form three primary bonds of 266 pm (0.33 vu), and six secondary bonds of 324-372 pm (Fig. 8.2(b)). In the process the radius of the coordination sphere increases from 297 to 322 pm in accordance with the distortion theorem (Rule 3.6). 

Other structural features that have acceleratory influences in the base hydrolysis of Co(III) systems are (i) the incorporation of a pyridine ligand in the coordination sphere and (ii) the incorporation of a flat secondary nitrogen donor system in the polyamine ligand skeleton (5) (structures C and D in Fig. 17). 

Among the derivatives of halide-substituted alcohols the fluoroalkoxides are of special interest. The presence of peripheral fluorine atoms enables the secondary M...F interaction and filling of the coordination sphere of the metal, which leads to an unusually high volatility. These compounds are described in the review by Willis [1749]. 

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