Design of Hydrophobic Polyoxometalate Hybrid Assemblies Beyond Surfactant Encapsulation (original) (raw)
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Surfactant-Encapsulated Clusters (SECs): (DODA)20(NH4)[H3Mo57V6(NO)6O183(H2O)18], a Case Study
Chemistry - A European Journal, 2000
We present a comprehensive study of the partially reduced polyoxomolybdate [H 3 Mo 57 V 6 (NO) 6 O 183 (H 2 O) 18 ] 21À encapsulated in a shell of dimethyldioctadecylammonium (DODA) surfactant molecules. Treatment of an aqueous solution of (NH 4) 21 [H 3 Mo 57 V 6-(NO) 6 O 183 (H 2 O) 18 ]´65 H 2 O (1 a) with a trichloromethane solution of the surfactant leads to instant transfer of the encapsulated complex anion into the organic phase. Results from vibrational spectroscopy, analytical ultracentrifugation, small-angle X-ray scattering, transmission electron microscopy, elemental analysis, and Langmuir compression iso-therms are consistent with a single polyoxometalate core encapsulated within a shell of 20 DODA molecules. The molar mass of the supramolecular assembly is 20 249 g mol À1 and the diameter is 3.5 nm. A material with the empirical formula (DODA) 20 (NH 4)[H 3-Mo 57 V 6 (NO) 6 O 183 (H 2 O) 18 ] (2) was isolated as a dark violet solid, which readily dissolves in organic solvents. Slow evaporation of solutions of 2 on solid substrates forces the hydrophobic particles to aggregate into a cubic lattice. Annealing these so-formed films at elevated temperature causes de-wetting with terrace formation similar to liquid crystals and block copolymers. Compound 2 forms a stable Langmuir monolayer at the air ± water interface; Langmuir ± Blodgett multilayers are readily prepared by repeated transfer of monolayers on solid substrates. The films were characterized by optical ellipsometry, Brewster angle microscopy, transmission electron microscopy, and X-ray reflectance.
ChemPhysChem, 2001
There are countless organic molecules that exhibit liquid crystalline behaviour. [1±4] Generally one distinguishes between thermotropic and lyotropic liquid crystals. The structural units in thermotropic liquid crystals are molecules mostly having elongated or disklike shapes, whereas in lyotropic liquid crystals the mesoscale organization is introduced by differences in cohesion energy density or selective solubility. To decrease the interfacial energy the solventophobic parts of amphiphilic molecules assemble to form distinct structures often with high symmetry and astonishingly long-range order, whereas the solventophilic parts are located on the outer surface of the structure and stabilize the system (for example, micellization of surfactants in aqueous solution).
Supramolecular architectures assembled from amphiphilic hybrid polyoxometalates
Dalton Transactions, 2012
Polyoxometalate (POM)-based inorganic-organic molecular hybrid clusters have been recently recognized as good candidates to design novel multi-functional materials. Tremendous efforts have been invested in synthesizing many interesting hybrid structures with exceptional chemical and physical properties. Grafting organic ligands to the POM clusters render these functional clusters amphiphilic properties. Here we summarize the current progresses and provide some perspectives, from colloidal chemists' point of view, on the self-assembly of the amphiphilic POM-organic hybrids in solution and at interfaces, as well as the related consequent novel features such as enhanced fluorescent properties. , where he is an associate professor of Chemistry. His laboratory focuses on the fundamental behavior of complex solutions, especially hydrophilic macroions, inorganic-organic hybrid surfactants, and other colloidal and biological systems. Fig. 1 Several well-characterized polyoxometalate clusters: (a) Lindqvist; (b) Anderson; (c) Keggin; (d) Dawson; and (e) {Mo 154 }.
Advanced Materials, 2000
Polyoxometalates (POMs) of transition metals (e.g., molybdenum, vanadium) have been a center of research interest for several decades, as they exhibit a great variety of structures and a rich diversity of fascinating properties. The structures range from relatively simple, like the Keggin ion, to extremely complex, such as the wheel-shaped [3±5] and ballshaped molybdate clusters prepared by Müller et al., of which the latter possess 154, 176, 248, or 132 metal centers per cluster. Their architectures are not only well-defined, relatively easy to produce, and beautiful, but these compounds also exhibit the electronic, electrochemical, magnetic, and optical qualities typical of mixed-valence molybdenum oxide compounds, which creates potential for many applications. 8] In most cases, pure POMs are quite difficult to handle from a materials science point of view. For example, the problem of too high a solubility in water is encountered, together with low pH and redox stability. In addition, the cluster cavities of most POMs are filled with water of crystallization, which cannot be removed without destroying the structures. [9,10] There is also the inherent problem of lacking access to all inner sites of the clusters, which is necessary for application of these compounds, for example in catalysis.
Inorganic Chemistry, 2001
New organic derivatives of "inverse-Keggin" polyoxometalate (POM) clusters, [Mo 12 O 46 (AsR) 4 ] 4-(R) C 6 H 4-4-COOH, C 6 H 3-4-OH-3-NO 2 , C 6 H 4-4-OH), have been synthesized. Structures of the corresponding sodium or iron salts were elucidated by single-crystal X-ray diffraction and shown to be 3D structures connected through hydrogen bonds and/or O-Na-O linkages. Parameters which influence the final solid-state architecture, such as the crystallizing solvent, organic moiety, and counterions, have been examined. The hydrogen-bonding ability of the solvent affects the connectivity of the POM clusters through interactions with the organic group and the inorganic core. The organic groups influence the structure through hydrogen bonds to other organic groups, to neighboring clusters, and/or to solvent molecules. Hydrogen bonding between the organic groups and the solvent appears to inhibit some possible connectivity patterns, such as the hydrogen-bonded dimerization of carboxylic acid groups. Na + ions were found directly bonded to the cluster oxo ligands and provided linkages between clusters. Larger cations, such as transition metals, did not show this interaction, and other bonding methods dominated.