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Title:Synthesis, structure, and reactivity of polyoxovanadates in nonaqueous media
Author(s):Yaghi, Omar M.
Doctoral Committee Chair(s):Klemperer, Walter G.
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Inorganic
Abstract:Exploration of the nonaqueous chemistry of polyoxovanadates was initiated by studying the following reaction: x $\rm H\sb3V\sb{10}O\sb{28}\sp{3-}$ + y OH$\sp-$ $\to$ 10 $\rm H\sb nV\sb xO\sb m\sp{z-}$ + (y-n) H$\sb2$O involving the addition of (TBA)(OH) to ($\rm H\sb3V\sb{10}O\sb{28}$)(TBA)$\sb3$ in CH$\sb3$CN, where TBA = tetra-n-butylammonium. This resulted in the synthesis and characterization of two types of soluble species: first, reactive isopolyvanadate species which can serve as good starting materials for the development of the synthetic chemistry of covalent polyoxovanadate derivatives; second, species which have structural features normally associated with those present on solid vanadium oxide surfaces. The first species isolated from this reaction was $\rm H\sb2V\sb{10}O\sb{28}\sp{4-}$ as a TBA salt, structural characterization in the solid and solution state reveal that the protonation sites are two OV$\sb2$ oxygens. This anion was found to be unstable in acetonitrile with respect to disproportionation forming two new polyoxovanadates, $\rm V\sb5O\sb{14}\sp{3-}$ and $\rm V\sb{12}O\sb{32}\sp{4-}$.
The $\rm V\sb{12}O\sb{32}\sp{4-}$ anion is formed as an acetonitrile inclusion complex, $\rm CH\sb3CN\subset(V\sb{12}O\sb{32}\sp{4-}$). The nido-$\rm V\sb{12}O\sb{32}\sp{4-}$ cage framework is a new structure type and can be derived from two different types of closo-cage frameworks. The vanadium coordination geometry within the $\rm V\sb{12}O\sb{32}\sp{4-}$ cage is similar to that observed in square-pyramidal vanadium(V) compounds such as orthorhombic $\rm V\sb2O\sb5$ and $\alpha$-VOPO$\sb4$.
The $\rm V\sb{12}O\sb{32}\sp{4-}$ is the first molecular inorganic species known to form inclusion complexes in solution. Synthesis and structural characterization of the $\rm CH\sb3NO\sb2$, $\rm C\sb6H\sb5NO\sb2$, p-$\rm CH\sb3C\sb6H\sb4CN$, $\rm C\sb6H\sb5CN$, $\rm NCCH\sb2CH\sb2CN$ and 1,2-$\rm CH\sb2CH\sb2Cl\sb2$ host-guest complexes has been achieved. The equilibrium constants for host-guest complexation have been derived, and in some cases the enthalpy and entropy of binding have been established quantitatively.
The structural analogy between orthorhombic $\rm V\sb2O\sb5$ layers and $\rm V\sb{12}O\sb{32}\sp{4-}$ host molecules, raises the possibility that this host framework might be capable of affecting C-H activation. Coordinatively unsaturated vanadium sites in vanadates such as $\rm (VO)\sb2P\sb2O\sb7$ can react with $\rm CH\sb3CN$ molecules. The remaining question is whether $\rm V\sb{12}O\sb{32}\sp{4-}$ can react with saturated hydrocarbons. (Abstract shortened with permission of author.)
Issue Date:1990
Rights Information:Copyright 1990 Yaghi, Omar M.
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9114471
OCLC Identifier:(UMI)AAI9114471

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