Molecular routes to metal oxides and metal silicates. Synthesis and thermal decomposition studies of eclipsed Mo{sub 2}[O{sub 2}Si(O{sup t}Bu){sub 2}]{sub 3} and W{sub 2}(NHMe{sub 2}){sub 2}[O{sub 2}Si(O{sup t}Bu){sub 2}]{sub 2}[OSi(OH)(O{sup t}Bu){sub 2}]{sub 2}
- Univ. of California, Berkeley, CA (United States)
Reaction of Mo{sub 2}(NMe{sub 2}){sub 6} with 3 equiv of ({sup t}BuO){sub 2}Si(OH){sub 2} afforded a new siloxide complex, Mo{sub 2}[O{sub 2}Si(O{sup t}Bu){sub 2}]{sub 3} (1), as the only metal-containing product. An X-ray crystal structure determination reveals that 1 adopts an eclipsed structure with three di-tert-butoxysilanediolato ligands bridging the molybdenum centers in a symmetrical fashion. Lewis acidic complex 1 forms an isolable adduct with pyridine. Reaction of W{sub 2}(NMe{sub 2}){sub 6} with 3 equiv of ({sup t}BuO){sub 2}Si(OH){sub 2} afforded W{sub 2}(NHMe{sub 2}){sub 2}[O{sub 2}Si(O{sup t}Bu){sub 2}]{sub 2}[OSi(OH)(O{sup t}Bu){sub 2}]{sub 2} (3), which was isolated as air-sensitive orange crystals. In this molecule, two O{sub 2}Si(O{sup t}Bu){sub 2} ligands bridge the W{triple_bond}W bond in an {eta}{sup 1}, {eta}{sup 1} fashion, and OSi(OH)(O{sup t}Bu){sub 2} ligands are coordinated to each W atom. This molecule adopts a highly eclipsed conformation and has a 2-fold axis of symmetry which perpendicularly bisects the tungsten-tungsten bond. Complex 1 undergoes a two-step weight loss (by TGA), which corresponds to the initial loss of isobutene and water (at ca. 200{degrees}C), followed by the loss of molybdenum by evaporation of MoO{sub 3} at 700-1050 {degrees}C. The pyrolysis of 1 at 550{degrees}C for 2 h under argon gave a ceramic material with the approximate formula Mo{sub 2}Si{sub 3}O{sub 10}. When the sample was heated at 1200 {degrees}C for 1 h, evaporation of MoO{sub 3} occurred and the final ceramic material had a composition of Mo{sub 0.5}Si{sub 3}O{sub 6.5}. Very low carbon contents for these materials are consistent with a clean elimination process during the pyrolysis. The material heated to 550 {degrees}C is amorphous, while the material taken to 1200 {degrees}C contains MoO{sub 2} as the only crystalline phase. 21 refs., 7 figs., 3 tabs.
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 563404
- Journal Information:
- Chemistry of Materials, Vol. 9, Issue 2; Other Information: PBD: Feb 1997
- Country of Publication:
- United States
- Language:
- English
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