Nitrogen bonds, covalent metal

Although metalloporphyrins are traditionally viewed as coordination complexes, their uncharged nature and covalent metal-nitrogen bonding are closely similar to organometallics, for instance... 

Tables 15 and 16 show the absorption maxima of some metal complexes of benzothiazolyl-substituted formazans 230 and 231.283 The wavelengths are metal ion dependent, making formazans useful reagents for the identification of specific metal ions or the simultaneous determination of two ions. The wavelengths are much longer than those of the formazan anion (Table 14). The general trend for electron-rich substituents is toward a larger shift this is to be expected as it tends to enhance the aromatic character of the ring and increase the covalent character of the metal — nitrogen bond. The sharpness of the absorption band has been attributed to coordination to the heterocyclic nitrogen as in 232.57S...

Until recently, the synthesis of ionic/covalent nitrides was relatively unexplored except for the pioneering work of Juza on ternary lithium nitrides.11 However, within the last decade, several groups have begun to explore ternary nitride systems, many of which have relied on the inductive effect. The inductive effect is based on the donation of electron density from an electropositive element to an adjacent metal-nitrogen bond, thereby increasing the covalency and stability of that bond and of the nitride material itself. The success of this method is illustrated by the fact that almost all of the known ionic/covalent ternary nitrides contain electropositive elements. Only recently has a small number of transition metal ternary nitrides been synthesized in the absence of the inductive effect at moderate temperatures, by taking advantage of low temperature techniques, such as the ammonolysis of oxide precursors and metathesis reactions.6,12-17... 

Covalent type MCMs with a metal-nitrogen bond (for instance, the products of the interaction of metal halides and alkoxides with allyl- and diallylamine, alkaline metal amides, etc.), a metal-sulfur bond and others have no wide uses in polymerization practice. 

A third alternative simply uses ferrocenes as walls in cyclophane-like structures.The ferrocenyl units typically are linked via flexible hydrocarbon chains appended to cyclopentadiene ligands. In other words, covalent carbon-carbon bonds rather than coordinate-covalent metal-nitrogen, - carbon, -oxygen, or -phosphorous bonds are used. 

The (Cl8TPP)uCo (d7sp) complex is unique with two metal-nitrogen (sp-p) covalent bonds and a metal-centered unpaired electron, which facilitates... 

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