Transition metal cations coordination number

Despite the weak basicity of isoxazoles, complexes of the parent methyl and phenyl derivatives with numerous metal ions such as copper, zinc, cobalt, etc. have been described (79AHC(25) 147). Many transition metal cations form complexes with Imidazoles the coordination number is four to six (70AHC(12)103). The chemistry of pyrazole complexes has been especially well studied and coordination compounds are known with thlazoles and 1,2,4-triazoles. Tetrazole anions also form good ligands for heavy metals (77AHC(21)323). 

Although Becher, Underhill, and co-workers (36—48) have prepared a number of macrocycles containing the tetrathiafulvalene redox center (Scheme 3) primarily designed to coordinate transition metal cations, no electrochemical recognition studies have as yet been reported. A tetrathiafulvalene-tetrasubstituted benzo-15-crown-5 ionophore (5) has... 

PL is a useful technique to characterize the coordination not only of transition metal cations, as described above, but also of oxide anions. A typical coordination of oxide anions in the bulk lattices of oxides can be defined by the number of nearest neighbor cations for octahedrally coordinated alkaline earth oxides, this number is 6. Ions of lower... 

In the case of transition metal cations, the coordinated water molecules are covalently bonded to the cation, and the coordination number can be interpreted as fixed in the absence of other ligands. If the cations Mn, Fe, Co, and Ni " " are assumed to be in the high spin state, then the effective radius of coordinated water molecules in these systems is 123 pm on the basis of the X-ray data. 

In the analysis of the mechanism of homogeneous catalytic reactions catalyzed by organometallic complexes, the number of vacant coordination sites at the transition metal cation is taken into account, required for the reactants to be coordinated (38). In the heterogeneous catalytic reaction, taking place at the surface of the solid the number of vacant coordination sites can vary either because of the location of the cation at different crystal faces or as the result of the generation of lattice defects. No information is available as to the role of either of these factors. 

A number of the distortions found in cation coordination environments are the result of electronic instabilities in the atoms themselves. Such distortions are typically found among the transition metal cations and the main group elements in low oxidation states. The origins of these instabilities are different and they... 

Ligands of the type (48) display a very large number of interesting coordination complexes with main group elements, transition metal cations, and /-element cations. This extensive chemistry has been thoroughly reviewed,... 

To address the acid-base properties of the transition-metal cations, we adopted the electronegativity scale for cations derived by Zhang (1982). Table 5 shows the electronegativities Xz for V , Ta and Nh>5+. The ratio Xz/CN, where CN refers to the coordination number of the cation, taken as being indicative of the acidity of the cations in their respective oxides, is the highest for V, followed by Ta and Nb . ... 

In propanediol-1,2-carbonate no asymmetric units are found since only [MBr4] and [VBr4], respectively were detected. Thus autocomplex formation of the bromides is complete in this solvent. The interaction of propanediol-1,2-carbonate with transition metal cations appears stronger than might be expected from a consideration of its donor number, which is only slightly higher than that of acetonitrile in this latter solvent many more coordination forms are produced. 

Free amino acids are able to coordinate transition metal cations via the carboxylate and the amino gronps. This is a well-estabUshed fact, which has been utilized for the design of synthetic receptors since a long time ago. In this regard, a number of examples can be fonnd in which metal complexes are at the core of the design of synthetic receptors for amino acids or other zwitterionic gnests... 

Cations in aqueous solution have the water molecules oriented toward them, and for small multivalent cations such as Mg " " and transition metal cations, this results in a coordinate bond in the first hydration shell. These water molecules form hydrogen bonds with molecules in a second hydration shell. Other cations, such as Ca " " and the alkali metal ones, do not have a definite number of coordinated water molecules but a distribution with a fi actional average number. 

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