M = Ba, Sr; R = Et; R' = lBu Figure 52. The tetranuclear structure of Ba2Ti2(thd)2(OEt)10(EtOH)4.

[576]. The transient oxo species formed in the transformation of the molecular cluster possess oxygen coordination numbers for the metals that are necessarily lower than those found for the extended solid-state structure of BaTiO3. As a consequence, the cluster grows (condenses) through oxygen supplied by the acetone molecules, a reaction called aldol condensation. The deficiency in oxygen coordination as the two alkoxide groups are replaced by an oxo unit provides a driving force for the cluster growth. A close look at the metal-oxygen core of the oxo-alkoxide molecule reveals a resemblance to a BaTiO3 structural subunit (Fig. 53). This structural similarity probably helps in lowering the barrier to a direct molecule-to-material conversion.

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