Coordinatively saturated atoms

Since the coordination number of tantalum or niobium in fluoride and oxyfluoride compounds cannot be lower than 6 due to steric limitations, further decrease of the X Me ratio (lower than 6) leads to linkage between complex ions in order to achieve coordination saturation by sharing of ligands between different central atoms of the complexes. The resulting compounds have X Me ratios between 6 and 4, and form crystals with a chain-type structure. 

The (010) face covers a large area of orthorhombic M0O3 crystallites apart from the edge atoms it contains only coordinatively saturated Mo and 0, the Mo-Oi being in the... 

In the field of porous supramolecular metal complexes, both molecular and extended-solid materials have been extensively studied in recent years. A particularly well-studied class of compounds is the metal-containing molecular squares, that is, square-shaped porous tetrameric structures (30,108). These have been prepared by several approaches, the most common being the reaction of an organic bridging ligand with a metal complex that has available cis-coordination sites (109-113) (Fig. 13). However, the resulting metal centers are usually coordinatively saturated, which makes it difficult for guest molecules to interact directly with the metal atoms. 

Oxygen-centered phosphanides are accessible by hydrolysis of the phospha-nides as shown for the oxygen-centered phosphanide 73 of the formula [Sr40- P(SiMe2Prl)2 6] with an Sr4P6 adamantane-like structure as shown in Eq. (7) [74], The strontium atoms are coordinatively saturated by agostic interactions to the silicon-bonded alkyl substituents. 

The structural features of the linear R-Cu-R arrangement are identical to those observed for other [R2CU] anionic units discussed previously (cf. Fig. 1.31). The [Li2CN(THF)2(PMDTA)2] cationic unit consists of a central cyanide moiety, to which two lithium atoms are bound in end-on fashion. Coordination saturation at each lithium atom is achieved by coordination of the three nitrogen atoms of the PMDTA molecule and one THF molecule, rendering each lithium atom penta-coordinate. Recent H, Li HOESY experiments showed that this ionic structure found in the solid state is probably retained in polar solvents such as THF [140]. 

In the absence of a donor solvent the coordinative saturation of the aluminum atoms can only be achieved by dimerization. Thus, the reaction of lithium trimethylsilyl-terf-butylhydrazide with dimethylaluminum chloride afforded the dimeric hydrazide 31 [Eq. (13)], which has a six-membered... 

There is considerable evidence that at least many of these reactions require coordinately unsaturated compounds to proceed. In those cases, a dissociation step may be the first part of the reaction. Then the.se coordinately unsaturated compounds react with an unsaturated molecule—it can be most anything as long as it has an available pair of electrons—and this inserting molecule goes in between the metal atom and one of the groups initially bonded to the metal. If the starting material is coordinately unsaturated, so is the product. A final step must be the formation of a coordinately saturated product by some final reaction, either with another ligand or by decomposition of this insertion product. 

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