Molecular complexity transition metal alkoxides

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... 

Another factor that influences reaction kinetics is the extent of oligomerization molecular complexity) of the metal alkoxides. The molecular complexity depends on the nature of the metal atom. Within a particular group, it increases with the atomic size of the metal (see Table 3), thus explaining the tendency of divalent transition metal alkoxides (Cu, Fe, Ni, Co, Mn) to polymerize rendering them insoluble [129]. Molecular complexity... 

Two principle strategies have been employed for the synthesis of siloxide-containing molecular precursors. The first involves a silanolysis, or condensation, reaction of the Si - OH groups with a metal amido, alkyl, hahde, or alkoxide complex. The second method involves salt metathesis reactions of an alkali metal siloxide with a metal hahde. Much of our work has been focused on formation of tris(tert-butoxy)siloxide derivatives of the early transition metals and main group elements. The largely imexplored regions of the periodic table include the lanthanides and later transition metals. 

The sol-gel chemistry of metal salts is more complex than that of metal alkoxides because of the numerous molecular species that can be formed depending on the oxidation state of the metal, the pH of the reaction solution and the concentration of the reactants. Since the sol-gel polymerization of inorganic salts varies widely among the different metal ions, this section will only present a general summary of the topic. For a detailed description of the mechanism of condensation and gelation, the reader is referred to the following review on the sol-gel chemistry of transition metal oxides [7]. 

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