Saturation, coordinative

The orange-red titanium acetylacetone chelates are soluble in common solvents. These compounds are coordinately saturated (coordination number equals 6) and thus much more resistant to hydrolysis than the parent alkoxides (coordination number 4). The alkoxy groups are the moieties removed by hydrolysis. The initial product of hydrolysis is beheved to be the bis-hydroxy bis-acetylacetone titanate, (HO)2Ti(acac)2, which oligomerizes to a... 

In this compound, synthesized in the low temperature reaction between diborane and excess ammonia, the cationic boron is coordinatively saturated in a tetrahedral environment. More recendy, cations having boron in tricoordinate or dicoordinate environments have been observed. These cationic species, called borenium and borinum ions, respectively, have been reviewed (19,20). 

The main synthetic route to high nuclearity metal carbonyl clusters involves a condensation process (/) a reaction induced by coordinatively unsaturated species or (2) a reaction between coordinatively saturated species in different oxidation states. As an example of (/), Os2(CO)22 can be condensed to form a series of higher coordinated species (89). 

The X-ray crystal structures of many of these complexes have now been determined representative examples are. shown in Fig. 4.11 from which it is clear that, at least for the larger cations, coordinative saturation and bond rhrectionality are far less significant factors than in many transition element complexes. Further interest in these ligands stems from their use in biochemical modelling since they sometimes mimic the behaviour of naturally occurring, neutral, macrocydic antibiotics such as valinomycin, monactin, nonactin, nigericin... 

Outer-sphere. Here, electron transfer from one reactant to the other is effected without changing the coordination sphere of either. This is likely to be the ea.se if both reactants are coordinatively. saturated and can safely be assumed to be so if the rate of the redox process is faster than the rates observed for substitution (ligand tran.sfer) reactions of the species in question. A good example is the reaction. 

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. 

A further decrease in the X Me ratio, to 4, leads to linkage of the octahedral units by sharing more than one ligand so as to achieve coordination saturation. Sharing of two vertexes (two comers of the each octahedron) leads to the formation of compounds with layered-type structures. 

The only significant difference between halide melts and oxyhalide melts is that oxyfluoride complexes have a tendency to dissociate at relatively high concentrations yielding polyanion groups. This phenomenon is related with the need to achieve coordination saturation. 

The solutions of mer-OsCl3(PR3)3 undergo an interesting reduction with zinc amalgam [155] to form OsCl2(PR3)2L (Figure 1.62), where L is a molecule abstracted from the atmosphere in the reaction flask if a noble gas, incapable of coordination, is employed, coordinative saturation is obtained by dimerization to [(PR3)3OsCl3Os(PR3)3]+. 

The 4 1 complexes tend to be formed only by less bulky phosphines and even then tend to be coordinatively saturated. 

Simple alkyls and aryls AuR are generally unstable but coordinative saturation ensures the stability of adducts Au(PR3)R ... 

Neutral transition-metal complexes that are not fully coordinatively saturated possess nucleophile metal centers capable of coordinating to electrophiles. On the other hand, group-IIIB halides serve as typical electron-pair acceptors and are, therefore, able to interact coordinatively with basic metal complexes. 

Metal-metal distances in supported metal clusters (e.g., It4, nearly 2.70 A) determined by EXAFS spectroscopy essentially match those in coordinatively saturated clusters of the same metal (e.g., Ir4(CO)i2). These distances are about O.2-O.3A greater than the metal-metal distances in the free (gas-phase) clusters (e.g., It4, 2.44 A) [32]. Similar results have been determined for supported OS5C [33] and Rhe [28,29]. 

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... 

Carter, E. A., Goddard III, W. A., 1988, Relationships between Bond Energies in Coordinatively Unsaturated and Coordinatively Saturated Transition Metal Complexes A Quantitative Guide for Single, Double, and Triple Bonds , J. Phys. Chem., 92, 5679. 

OPh, or Ome x = 1, 2, or 3] (47). The carboxylation reaction was favored when the ratio of tertiary phosphine to copper salt was increased to 3 1. This suggests that an intermediate Cu—(C02) complex is not formed. At this ratio the copper complexes are considered coordinately saturated. Carboxylation was also favored when phosphines of high o- donor ability were used. 

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