The Alkoxides of Molybdenum, Tungsten and Vanadium and their Hydrolysis Products
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VADIM G. KESSLER*, EUGENIA P. TUREVSKAYA*, SERGEI I. KUCHEIKO*, NATALYA I. KOZLOVA*, NATALIYA YA. TUROVA*, IRINA E. OBVINTSEVA** AND MARY I. YANOVSKAYA**
*M.V.Lomonosov Moscow State University, Department of Chemistry 117234 Moscow, Russia **L. Ya. Karpov Institute of Physical Chemistry, 117813 Moscow, Russia
INTRODUCTION The increasing interest in the chemistry of early transition metals alkoxides originates from
the possibility of their application as versatile molecular precursors of inorganic oxide materials in MOCVD or sol-gel processes [1-31. Nevertheless the derivatives of such elements as V (especially in lower oxidation states), Mo and W remained poorly explored until recently. This seems to be a result of very diverse (for each of these elements one can imagine several series of homo- and heterometallic alkoxide complexes corresponding to ortho- M(OR)n, Oxo-MO(MO)no2 or dioxo- MO2(OR)n-4 formulations, to which the high stability of a multiple M=O bond is giving rise) and very complicated (due to various side reactions) chemistry. The use of these derivatives in sol-gel processing would provide a facile approach to such materials as Bi20 3W03 (solid solutions) - solid electrolytes; LixWO 3, W0 3, MoO 3 - photosensors and photo- and electrochromes; Bi2MO6 (M=Mo, W) Ln20 3.3MoO 3 - ferroelectrics; M'2MO4, MlIM0 4 (M'=Li, Na; M"=Mg-Ba; M= Mo, W)- dielectrics etc [1]. The high chemical reactivity of the title compounds simplifies the investigation of their mechanisms and thus provides the key to understanding some general trends in the chemistry of metal alkoxides in general. The present report presents the results of a systematic study of the synthesis, physical and chemical properties of V, Mo and W alkoxides and the principles of their application in the preparation of the related oxide materials.
1. SYNTHESIS It is worth noting that different synthetic routes lead to different series of alkoxide compounds. None are able to prepare V(OR)s, very mild conditions (MoF 6 co-condensation with RnSi(OR) 4.n at -700C) are necessary to obtain Mo(OMe)6 [4], while the conventional techniques
described below provide access to oxoalkoxides of both V(V) and Mo(VI) and orthoalkoxides of V(IV) and W(V and VI) (see Table 1), thus illustrating that the multiple M=O bond stability increases in the row W < Mo < V and decreases with decreasing oxidation state.
1.1 Esterification M2 0n + RO (+R' 4NX) -- to-> MOx(OR)y + H20 + (+...) [5,6,7]
3 Mat. Res. Soc. Symp. Proc. Vol. 346. 01994 Materials Research Society
It takes place for acidic M20n = V2 0 5 , MoO 3 2H 2 0. It was found effective to prepare polyoxoalkoxometallates like [V10O 13{EtC(CH20) 3} 5]- [8] or [Mo 4 0j0 (OMe) 6 ]2 - [9].
1.2 Alcoholysis of metal halids MCIn + ROH
- -HCI
->
We have proved it to be always accompanied by RCI or oxochloride solvates: VC14 + nROH -
-HCI ->
MoCI5 + nROH -
-HCI
WCI6 + 4ROH -
->
[10]
MCIn. 2 (OR)2 "xROH
[VCI3 (OR)]
-
-RCI
[MoCI 4 (OR)] -
-4HCI _> W(OR) 4 CI2 -
The identity of the products was proved by IR and X-
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