Coordination bonds, between transition

Coordination bonds, between transition metal atoms and ligating atoms, 27 72-76 Coordination chemistry, of oligopyridines, see Oligopyridines, coordination chemistry Coordination complexes covalent binding in, 5 13-15 fluorocyclic derivatives, 15 346-368 Coordination compounds... 

Compounds with Bonds between Transition Metals and Three-Coordinate Gallium, Indium, and Thallium... 

The insertion of unsaturated molecules into metal-carbon bonds is a critically important step in many transition-metal catalyzed organic transformations. The difference in insertion propensity of carbon-carbon and carbon-nitrogen multiple bonds can be attributed to the coordination characteristics of the respective molecules. The difficulty in achieving a to it isomerization may be the reason for the paucity of imine insertions. The synthesis of amides by the insertion of imines into palladium(II)-acyl bonds is the first direct observation of the insertion of imines into bonds between transition metals and carbon (see Scheme 7). The alternating copolymerization of imines with carbon monoxide (in which the insertion of the imine into palladium-acyl bonds would be the key step in the chain growth sequence), if successful, should constitute a new procedure for the synthesis of polypeptides (see Scheme 7).348... 

The term metallomesogen is often used when a (transition) metal is complexed (by coordinative bonds between the crown heteroatoms and the metal center) by a crown ether. These compounds were discussed in the previous sections as complexed crown ethers (instead of metallomesogens ) together with their uncomplexed precursors. In this section, mesogens with a covalent bond between... 

Transition Metal Compounds. - Dobado et al.119 used AIM to study the electronic properties of seven isomers of three-coordinated copper(I) thiocyanates, calculated at MP2 and B3LYP level using the 6-311 + G basis set. The results indicate that in the gas phase N-bonding is preferred to S-bonding. The coordination bond between the Cu(I) cation and the donor atoms is strongly polarised, almost ionic. The charge depletion around the Cu(I) cation is in accordance with sp2 hybridisation. Moreover, the canonical form for the non-coordinated as well as S-coordinated thiocyanates is mainly S-C=N, whereas the N-bonded thiocyanates have also N=C—S contribution. 

Crystal engineering of coordination pol5rmers using 4,4 -bipyridine as a bond between transition metal atoms 06CC4169. 

The predicted electronic transitions in the Ib complex, described in [21], indicate the formation of a coordination bond between molecular iodine and the glycine carboxyl group. This results in their contribution towards short wave band at 212-257 nm (Table 10.1). 

We have seen that the crystal-field model provides a basis for explaining many features of transition-metal complexes. In fact, it can be used to explain many observations in addition to those we have discussed. Many lines of evidence show, however, that the bonding between transition-metal ions and ligands must have some covalent character. Molecular-orbital theory (Sections 9.7 and 9.8) can also be used to describe the bonding in complexes, although the application of molecular-orbital theory to coordination compounds is beyond the scope of our discussion. The crystal-field model, although not entirely accurate in all details, provides an adequate and useful first description of the electronic structure of complexes. 

The concept of bond polarity, which is used in main group chemistry with reference to electronegativities of the atoms involved, is less readily applied in a quantitative way to bonds between transition metals. Their nature may be more significantly influenced by the coordination spheres of the metal centers involved rather than intrinsic properties of the metal itself. This increased level of sophistication required in a meaningful discussion of bond polarity in M-M bonds necessitates elaborate quantum chemical methods to be used. However, this may render it difficult to extract information from the results of such calculations, which are interpretable within the established paradigms of structure and bonding familiar to the chemist. 

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