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Metal Alkoxides

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  • Großansicht:
    Octakis(tert-butoxo)dicerium(IV) [Ce2(OtBu)8] https://doi.org/10.1021/ic4025876
  • Großansicht:
    Dimeric Termetallic [{Cd(OPri)3}Ba{Zr2(OPri)9}]2. https://doi.org/10.1021/ja953255z

One main area of interest in our working group is the preparation of functional oxide nanomaterials. To gain optimized material properties the bottom-up approach, using custom-designed precursors, outmatches in many fields the classical top-down approach using cutting, milling or shaping of the bulk material. The use of metal organic compounds as precursors facilitates in general low temperature processing of nanostructured oxide materials that are often more challenging to obtain using traditional solid-state reactions. Based on the intention to obtain very homogeneous, highly pure and crystalline multimetallic materials via solution or gas phase methods as for instance sol-gel or chemical vapor deposition (CVD) processes, the use of single-source precursors is clearly favored over a multi-source approach.

In this context, alkoxide precursors play a major role due to their structural diversity resulting from their nature to exist in different coordination or bridging modes that allow the construction of homonuclear multimetallic oligomers and also heteronuclear compounds. The general increasing interest in heterometallic frameworks can be satisfied by a smart utilization of characteristic alkoxide features as predefined M–O bonds and the coordination tendency of alkoxo oxygen atoms. These features not only provide the possibility to improve physical properties such as solubility and volatility of the new compounds by defined changes in the molecular structure of the precursor, but also enable versatile prospects for the transfer of structural information from the precursor to the final solid-state material. The predefined metal-oxygen bonds in alkoxide compounds allow the construction of a molecular template that resembles the connectivity and arrangement of elements for the targeted oxide material already on a molecular level. Induced self-assembly of these single molecule templates by controlled decomposition (CVD) or controlled hydrolysis (sol-gel) ideally results in the construction of target solid-phase materials.

Extensive investigations in alkoxide chemistry revealed recurrent structural motifs of various alkoxometallate anions. These observations led to the establishment of the so-called molecular building block concept , in which the alkoxometallate units act as ligands with variable denticity and are usually transferred under retention of structural configuration to electropositive metals or alkoxo metallate fragments. The versatility of coordination modes for those polydentate ligands allow a diversified operation for ligating a second metal. Typical and important alkoxometallate building blocks are {M(OR)3}, {M(OR)4}-, {M(OR)5}-, {M(OR)6}- and {M2(OR)9}-, which are used for the preparation of various mono-, bi-, and trimetallic alkoxides. 

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