| CONCLUSIONS
Among the various precursors of metal oxides
namely metal b-diketonates and metal
carboxylates, metal alkoxides are the
most versatile. They are available for nearly all elements and
cost-effective synthesis from cheap feedstoks have been developed for some.
The selection of appropriate OR groups -bulky, functional, fluorinated (ORf)
allows to tune their properties. A large range of mixed-metal compositions
is accessible in mild conditions, often at RT, by mixing metal alkoxides (or
oxoalkoxides) and other oxide precursors. Well-defined "single-source"
precursors of MTiO3 (M = Pb, Ba, Sr) for instance are known. The choice of
an OR group, of an other ligand, acetate or
b-diketonate, is not innocent
for getting precursors having the right stoichiometry between the metals by
Lewis acid-base reactions. One can notice the importance of the oxo ligand
due to the versatility of its coordination modes and it can be essential for
reactivity. The various ligands play an important role for transformation
into materials which remains to be better understood.
For elements others than silicon and tin,
precursors bearing functionalities require linkage to the metal via oxygen
atoms (O-donor ligands). Compounds with polymerizable sites accessible for
copolymerization are available for some metals (Ti, Zr, Nb, Ln) as well as
for some mixed-metal (Ti-Zr) species. Metal alkoxides represent also a
potential for materials beyond oxides, such as phosphates or sulfides.
Functional metal carboxylates have been
developed in order to overcome solubility hurdles. They can represent
alternatives to metal alkoxides if formation of stable carbonates, a
favoured decomposition pathway for such ligands, does not preclude low
temperature crystallisation.
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