Hybrid Polyoxometalates: Merging Organic and Inorganic Domains for Enhanced Catalysis and Energy Applications (original) (raw)
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On the design of a planar oxo matrix for binding transition metals: a density functional approach
Journal of Molecular Structure: THEOCHEM
Density functional theory method is applied to investigate the geometry and electronic structure of a molecular system considered as a model of a metal±oxo surface. Vanadyl cation complexed by 2-hydroxyisonaphthalic acid is chosen as a building block, which gives an extended layer-type structure where planar, dimeric units are held together by a platinum or zirconium atom. The resulting two metal-linked two-dimer systems can be used as suitable model systems for polyoxomatrices, where the coordination around both platinum and zirconium atoms is square-planar. The electronic structures point out unpaired electrons which are responsible for magnetic interactions occurring mainly within isolated dimeric units for platinum system and with a more complicated spin distribution between adjacent dimers in the plane for zirconium system.
Journal of the American Chemical Society, 2012
The chemical system based on the [Mo 2 O 2 S 2 (OH 2 ) 6 ] 2+ aqua cation (noted L) and the trivacant [AsW 9 O 33 ] 9polyoxometalate (noted POM) has been investigated. Depending upon the ionic strength and the nature of the alkali cations, these complementary components assemble to yield three different architectures derived as hexamer , tetramer (2), and dimer (3). This series of clusters displays the same stoichiometry {POM 6 L 9 } 36-, {POM 4 L 6 } 24-, and {POM 2 L 3 } 12for 1, 2, and 3, respectively, and their conditions of formation differ mainly by the nature and the concentration of the alkali cation (from Li to Cs). Structural characterizations of 1 reveal a large hexameric supramolecular scaffold (about 25 Å in diameter), which encloses a large internal hole (about 200 Å 3 ) filled by water molecules and alkali cations (Na + or K + ). The hexameric scaffold 1 exhibits a rare flexibility property evidenced in the solid state by two distinct conformations, either eclipsed (1a) or staggered-off (1b). Both conformations appear clearly separated by a large twist angle (∼40°) and depend mainly on the composition of the internal hole. Structure of anion 2 shows a tetrahedral arrangement where the four POM units and the six connecting {Mo 2 O 2 S 2 } linkers are located at the corners and at the edges, respectively. The structure of anion 3 corresponds to the simplest arrangement, described as a dimeric association of two POM units linked by three {Mo 2 S 2 O 2 } pillars. Stability of the hexameric scaffold has been investigated in solution by 183 W and 39 K NMR and by UV−vis, showing that stability of 1 depends strongly on the proportion of potassium ions, which interfere through host−guest exchange. Density functional methodology (DFT) has been applied to compute the geometries and energies of dimer (3), tetramer (2) and hexamer (1) based on {AsW 9 O 33 } (POM) and {Mo 2 O 2 S 2 } (L) units. Calculations tend to show that internal cations act as "glue" to maintain the POM units connected through the conformationally inward-directed {Mo 2 O 2 S 2 } linkers.
Modular Inorganic Polyoxometalate Frameworks Showing Emergent Properties: Redox Alloys
Angewandte Chemie, 2010
The targeted synthesis of new extended modular frameworks exhibiting specific properties is a principal challenge of modern chemistry research. [1] Many inorganic frameworks and metal-organic frameworks (MOFs) have been reported, but the fine manipulation of their electronic properties remains challenging. One such approach could be the development of molecular alloys, analogous to metal alloys, yet this idea has rarely been applied, and three dimensional (3D) framework alloys based upon molecular building blocks have not yet been fully realized. Conceptually, the design of 3D framework alloys could be achieved if the components of two isostructural frameworks "A" and "B" could be mixed at the molecular level (in any proportion) forming a crystal of AB units, perfectly arranged, so the AB alloy is also isostructural to frameworks A and B. [9] The potential applications of such an approach are highly appealing, since the combination of coordination-compound-based building blocks, exhibiting different electronic properties, could allow the targeted tuning of frameworks with properties intermediate between A and B; and even the realization of "emergent" or unexpected properties for the alloy.
Journal of Catalysis, 1989
In complement to Part I, theoretical MO calculations (EHMO level) show that the main factor which influences the electronic energy levels of polyoxomolybdates is not always the local MO symmetry (tetrahedral or octahedral). The effect of protonation and/or grafting on a surface oxide is weak but slightly larger for tetrahedral than for octahedral species and could lead to wrong attributions. The condensation of several sites in polyoxomolybdates has a greater effect since it involves a MO delocalization over the whole compound, and therefore a loss of the individuality of each octahedral or tetrahedral unit. It leads to a decrease in the HOMO-LUMO gap yielding to an absorption red shift. The effect of distortion of local symmetry by bond elongation tends to decrease the HOMO-LUMO gap in an isolated species. In a condensed system, this distortion lowers the MO-MO interactions and moderates the red shift due to the effect of condensation. This latter effect, however, remains predominant. o 1989 Academic PXSS, IX.
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.