Supramolecular Organization in Organic鈥揑norganic Heterogeneous Hybrid Catalysts Formed from Polyoxometalate and Poly(ampholyte) Polymer

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• 作者：Gijo Raj ; Colas Swalus ; Alain Guillet ; Michel Devillers ; Bernard Nysten ; Eric M. Gaigneaux
• 刊名：Langmuir
• 出版年：2013
• 出版时间：April 2, 2013
• 年：2013
• 卷：29
• 期：13
• 页码：4388-4395
• 全文大小：467K
• 年卷期：v.29,no.13(April 2, 2013)
• ISSN：1520-5827

文摘

Hybridization of polyoxometalates (POMs) via the formation of an organic鈥搃norganic association constitutes a new route to develop a heterogeneous POM catalyst with tunable functionality imparted through supramolecular assembly. Herein, we report on strategies to obtain tunable well-defined supramolecular architectures of an organic鈥搃norganic heterogeneous hybrid catalyst formed by the association of a hydrophobically substituted polyampholyte copolymer (poly N, N-diallyl-N-hexylamine-alt-maleic acid) and phosphotungstic acid (H₃PW₁₂O₄₀) POMs. The self-assembling property of the initial polyampholyte copolymer matrix is modulated by controlling the pH of the hybridization solution. When deposited on a mica surface, isolated, long and extended polymer chains are formed under basic conditions (pH 7.9), while globular or coiled structures are formed under acidic conditions (pH 2). The supramolecular assembly of the POM-polymer hybrid is found to be directed by the type and quantities of charges present on the polyampholyte copolymer, which themselves depend on the pH conditions. The hypothesis is that the Keggin type [PW₁₂O₄₀]^{3鈥?/sup> anions, which have a size of 1 nm, electrostatically bind to the positive charge sites of the polymer backbone. The hybrid material stabilized at pH 5.3 consists of POM-decorated polymer chains. Statistical analysis of distances between pairs of POM entities show narrow density distributions, suggesting that POM entities are attached to the polymer chains with a high level of order. Conversely, under acidic conditions (pH 2), the hybrid shows the formation of a core鈥搒hell type of structure. The strategies reported here, to tune the supramolecular assembly of organic鈥搃norganic hybrid materials, are highly valuable for the design and a more rational utilization of POM heterogeneous catalysts in several chemical transformations.}