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Research article2008Peer reviewed

Synthesis of highly sterically hindered niobium and tantalum alkoxides and their microhydrolysis in strongly basic medium

Donat, Marco; Seisenbaeva, Gulaim A.; Kessler, Vadim G.


We have investigated the interaction of niobium and tantalum alkoxides with pinacol and are reporting here isolation and structural characterization of the products, attractive potential precursors of materials with hierarchical porosity. The general feature in the reactivity of alkoxide complexes with additional ligands is that stabilization of the complexes is achieved due to Bronsted acidity of the ligand and possibility of formation of hydrogen bonds in the structure. Presence of strong organic bases does not influence the complex formation. We were able to isolate, for example, highly moisture-sensitive ortho-pinacolates of Nb and Ta, M(O(2)C(6)H(12))(2)(OC(6)H(12)OH), in the presence of excess of triethylamine. The earlier attempts to prepare these complexes were unsuccessful because of extremely high solubility and easy hydrolysis of these species. The first step in microhydrolysis of M(O(2)C(6)H(12))(2)(OC(6)H(12)OH), M = Nb, Ta, independently of basicity of the medium provides M(2)O(O(2)C(6)H(12))(2)(OC(6)H(12)OH)(4), even those highly moisture-sensitive in solution. The general conclusion of this work is that the Lewis acidity and blocking of the coordination sites by bulky alkoxide ligands does not play any important role. The reactivity of the species is not in any way hindered by the complete blocking of the metal centers.


niobium; tantalum; pinacolate; X-ray structure; Lewis acid; Lewis base; hydrolysis and condensation mechanism; MTSAL concept

Published in

Journal of Sol-Gel Science and Technology
2008, Volume: 48, number: 1-2, pages: 61-65
Publisher: SPRINGER