Metal alkoxides molecular complexities

Overall, the alkali metal alkoxide and aryloxide systems are excellent examples in demonstrating the effects of steric influences on both molecular aggregation and also on the nature of any extended network architecture adopted. The large database of O-M complexes that have now been identified has led to a good deal of predictability regarding the coordination chemistry of these species. 

The hydrolysis of early transition metal alkoxides is an extremely facile reaction that makes the manipulation of these materials non-routine. The typical insolubility and high molecular complexity... 

In 1950s and 1960s Bradley developed the structure theory for metal alkoxides, based on the principle that metal atoms should achieve maximal coordination at minimal molecular complexity of the aggregate, [M(OR) ]m. 

Experimental studies of the structures of metal alkoxides started more than 40 years ago. The very first study of this kind was made at Moscow State University in 1957 by Struchkov and Lobanova and was devoted to the investigation of W(OPh)6 [1358], During the last 20 years work in the field of structural studies of metal alkoxides and phenoxides has been intensified. At present more than 1000 structures of the derivatives containing exclusively OAlk- and OAr- functional groups have been described. We consider them in relation to their molecular complexity beginning with the monomers and finishing with polymers. ... 

The interaction of the metal alkoxides with the salts of carboxylic acids or with p-diketonates of other metals is especially attractive for the synthesis of bimetallic molecular precursors in the cases, when the preparation of the alkoxide of the other metal is somehow hindered or it is insoluble or irreactive under the conditions applied. This method has been widely used for the sol-gel preparation of HTSC materials (because of low solubility and reactivity of Cu(OR)2) and lead-containing ferroelectrics (in the view of difficult synthesis and low stability of Pb(OR)2). It should be mentioned that the reaction between a metal alkoxide and a functional derivative does far not always lead to the formation of a mixed-ligand bimetallic complex ... 

The data accumulated on properties of Nb and Ta alkoxides studied in detail permitted the connection to be traced between the molecular complexity and the boiling points for different members ofthe homologous series, which allowed some general conclusions to be made concerning the trends in the homologous series in general (see Chapter 3). Concerning the vapor pressures and the possibility of purification by distillation, see [205]. The evaporation enthalpies for methoxides, ethoxides, and n-propoxides of the 2 metals are... 

The molecular complexity of molybdenum (IV) alkoxides is determined by the size and ramification of the alkyl group — the polymeric (R = Me), dimeric (CN = 5, two bridging OR-groups, R = Pr ) with a double metal-metal bond, and even monomers (R = Bu ). The first representatives of W(OR)4 homologous series are tetramers with the [Ti4(OMe)16]-type structure. The derivatives of ramified or bulky alcohols are known only as mixed-ligand complexes (such as dimeric solvates of alkoxide halids with alcohols, various alkoxide hidrides and monomeric complexes with phenantroline, see Table 12.19). 

The use of Cp or Cp -based ligands is also beneficial for the iron-based systems in controlling radical polymerization. For instance, FeCpI(CO)2 (Fe-3, X = I) induced a living radical polymerization of styrene in conjunction with an iodide initiator [(CH.s C-(C02C2H5)I] in the presence of Ti(Oi-Pr)4 to give very narrow MWDs (MJMn =1.1) and controlled molecular weights.72 The rate was increased with the use of the corresponding bromide, while the MWD was narrowed by replacement of Cp with Cp. 73 A faster and controlled polymerization was possible with dinuclear Fe(I) complexes (Fe-5 and Fe-6) in the absence of metal alkoxides. 

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