Physicochemical approach to the studies of metal alkoxides

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The review provides a description of main events in the development of chemistry of metal alkoxides in Russian and summarizes the results obtained by the authors. The studies of solubility and vapor pressure in the M(OR) n -ROH (R  Li, Mg, Ca, Sr, Ba, Tl) systems permitted the determination of the composition of the solvates formed and the optimization of the isolation conditions for distinct derivatives. The electrochemical synthetic approach to the alkoxide and 2-methoxyethoxide derivatives of III–VIII Group elements has been elaborated. Improvement of the MCl n with NaOR metathesis conditions led to practically quantitative yields of alkoxides. The examples of the structures of polynuclear oxoalkoxides, earlier erroneously considered to be orthoderivatives, i.e. ‘M(OR) n ’, are given. It has been stated that among the alkoxoderivatives of Zr and Hf these are only M(OC 2H 4OMe) 4 and M(OR) 4·ROH (RPr i , Bu i ) that exist as individual compounds, while the samples of those with different R contain oxocomplexes of M 3O(OR) 10 and M 4O(OR) 14 composition. The questions connected with the origin of oxogroups in the molecules of alkoxides and their influence on the properties of the samples are discussed. The irreproducibility of the physicochemical constants for the samples (physical state, melting points, solubility in alcohols, intensity of coloration) is caused by different ‘chemical’ (synthetic procedures, isolation conditions) and the thermal prehistory and storage times; it originates from the difference in their molecular composition (different fractions of different types of oligomeric and polymeric [M(OR) n ] m and M x O y (OR) z aggregates). Formation of bimetallic alkoxides is studied using the plotting to 20°C solubility isotherms in M(OR) n − M′(OR) m -Solvent systems. Different kinds of systems are considered and the composition and structure of bimetallic complexes and oxocomplexes, originating from their decomposition, are described. Decomposition of alkoxomolybdates and -tungstates in solution may result in crystallization of complex oxides as the final products. The example of MTiO 3 (MMg, Ba) oxide preparation is discussed as most illustratively demonstrating the need in studies of metal alkoxides interaction in solution for the optimization of synthesis of oxides by the sol-gel technique.