School of Chemistry - Research Publications
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ItemHoch fluoreszierende Pyridiniumbetaine für die Lichtsammlung(Wiley, 2017-10-23)Abstract Die Ergebnisse experimenteller und theoretischer Untersuchungen der Eigenschaften von Pyridiniumenolaten werden vorgestellt, und ihre potenzielle Nutzbarkeit in Lichtsammelanwendungen, insbesondere lumineszierenden Solarkonzentratoren (LSCs), wird demonstriert. Synthesen, Strukturen, photophysikalische Charakterisierung und wellenfunktionsbasierte quantenchemische Studien für fünf Cyclobetaine werden präsentiert und die Leistungsfähigkeit einer LSC‐Apparatur, die eines dieser Cyclobetaine enthält, wird mit dem aktuellen Stand der Technik verglichen.
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ItemHighly Fluorescent Pyridinium Betaines for Light Harvesting(WILEY-V C H VERLAG GMBH, 2017-10-23)We report the findings of our experimental and theoretical investigations into the properties of pyridinium enolates and their potential utility in light-harvesting applications, such as in luminescent solar concentrators (LSCs). We present the synthesis, structures, photophysical characterization, and wavefunction-based quantum-chemical studies of five cyclobetaines. The performance of an LSC device incorporating one of these cyclobetaines is shown to be comparable to state-of-the-art devices.
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ItemMixed-Metal Hybrid Polyoxometalates with Amino Acid Ligands: Electronic Versatility and Solution Properties(AMER CHEMICAL SOC, 2016-12-05)Eight new members of a family of mixed-metal (Mo,W) polyoxometalates (POMs) with amino acid ligands have been synthesized and investigated in the solid state and solution using multiple physical techniques. While the peripheral POM structural framework is conserved, the different analogues vary in nuclearity of the central metal-oxo core, overall redox state, metal composition, and identity of the zwitterionic α-amino acid ligands. Structural investigations reveal site-selective substitution of Mo for W, with a strong preference for Mo to occupy the central metal-oxo core. This core structural unit is a closed tetrametallic loop in the blue reduced species and an open trimetallic loop in the colorless oxidized analogues. Density functional theory calculations suggest the core as the favored site of reduction and reveal that the corresponding molecular orbital is much lower in energy for a tetra- versus trimetallic core. The reduced species are diamagnetic, each with a pair of strongly antiferromagnetically coupled MoV centers in the tetrametallic core, while in the oxidized complexes all Mo is hexavalent. Solution small-angle X-ray scattering and circular dichroism (CD) studies indicate that the hybrid POM is stable in aqueous solution on a time scale of days within defined concentration and pH ranges, with the stability enhanced by the presence of excess amino acid. The CD experiments also reveal that the amino acid ligands readily exchange with other α-amino acids, and it is possible to isolate the products of amino acid exchange, confirming retention of the POM framework. Cyclic voltammograms of the reduced species exhibit an irreversible oxidation process at relatively low potential, but an equivalent reductive process is not evident for the oxidized analogues. Despite their overall structural similarity, the oxidized and 2e-reduced hybrid POMs are not interconvertible because of the respective open- versus closed-loop arrangement in the central metal-oxo cores.
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ItemPhotocoloration in Hybrid Amino Acid Polyoxometalates(WILEY-V C H VERLAG GMBH, 2019-01-31)The study of four different salts of a hybrid glycine–polyoxotungstate has revealed photocoloration that is dependent on the intramolecular hydrogen bonding between glycine ligand ammonium groups and the polyoxotungstate. Four compounds comprised of the hybrid polyoxometalate [As4{W3Y}W44Y4O159(Gly)8(H2O)12]9– (Gly = glycine) with glycinium, benzylammonium, 4‐methylbenzylammonium, or benzyltriethylammonium countercations have been synthesized and structurally characterized. In the solid state, two of the compounds exhibit coloration associated with photoreduction, cycling from white to blue under UV irradiation, and bleaching back to white following reoxidation in air. The ability of the hybrid POM to undergo photoreduction correlates with the orientation of the zwitterionic ammonium groups of the glycine ligands and the intramolecular hydrogen bonding to POM oxo ligands. The kinetics of coloration of these POMs follows a pseudo‐second‐order rate law.
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ItemNichtwässrige mikrowellengestützte Synthesen von Deca‐ und Hexamolybdovanadaten(Wiley, 2017-07-10)Abstract Ein neuer Ansatz zur Synthese von Heterohexa‐ und Heterodecametallaten unter nichtwässrigen, mikrowellengestützten Reaktionsbedingungen wurde entwickelt. Die zwei neuartigen Molybdovanadate wurden isoliert und im festen sowie gelösten Zustand mittels Einkristall‐Röntgenbeugung, FT‐IR‐, UV/Vis‐ und multinuklearer NMR‐Spektroskopie sowie ESI‐MS charakterisiert. Die relativen Stabilitäten der möglichen Strukturisomere beider Polyoxometallatsysteme wurden mithilfe von dispersionskorrigierten DFT‐Rechnungen untersucht.
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ItemNon-Aqueous Microwave-Assisted Syntheses of Deca- and Hexa-Molybdovanadates(Wiley, 2017-07-10)We report a new approach for the synthesis of heterohexa‐ and heterodecametalates via the use of non‐aqueous, microwave‐assisted reaction conditions. The two novel molybdovanadates have been isolated and characterized in the solid and solution states using single‐crystal X‐ray diffraction, FT‐IR, UV/Vis, multinuclear NMR spectroscopy, and ESI‐MS. The relative stabilities of the possible structural isomers were probed using dispersion‐corrected DFT calculations for both polyoxometalate systems.
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ItemNo Preview AvailableA Heteroaromatically Functionalized Hexamolybdate(MDPI - Open Access Publishing, 2015-05-08)A new heteroaromatic thiophene containing organoimido functionalized hexamolybdate has been synthesized and characterized in both solid form and solution. Structural analysis shows successful introduction of the organoimido ligand through replacement of one terminal oxo site on [Mo6O19]2− to yield the singly functionalized hexamolybdate. Spectroscopic and theoretical analysis indicates charge transfer between the inorganic and organic components, with a significantly red-shifted lowest lying transition of 399 nm vs. the parent Lindqvist ion of 325 nm. Additional characterization includes, thermal gravimetric analysis (TGA), infrared (IR), cyclic voltammetry (CV), nuclear magnetic resonance (NMR) and time-dependent density functional theory (TD-DFT) studies.
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ItemBoronic acid and boronic ester containing polyoxometalates(ROYAL SOC CHEMISTRY, 2016-12-21)Three organoboron functionalized polyoxometalates have been synthesized using Schiff base chemistry including a boronic acid, its methyl ester and its trimethylene glycol ester. The compounds have been characterized in the solid state by single crystal diffraction (XRD), FT-IR and elemental analysis and in solution using 1H NMR spectroscopy.
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ItemPolyoxometalate - conductive polymer composites for energy conversion, energy storage and nanostructured sensors(ROYAL SOC CHEMISTRY, 2015)The exchange of electric charges between a chemical reaction centre and an external electrical circuit is critical for many real-life technologies. This perspective explores the "wiring" of highly redox-active molecular metal oxide anions, so-called polyoxometalates (POMs) to conductive organic polymers (CPs). The major synthetic approaches to these organic-inorganic hybrid materials are reviewed. Typical applications are highlighted, emphasizing the current bottlenecks in materials development. Utilization of the composites in the fields of energy conversion, electrochemical energy storage, sensors and nanoparticle "wiring" into conductive materials are discussed. The outlook section presents the authors' views on emerging fields of research where the combination of POMs and CPs can be expected to provide novel materials for groundbreaking new technologies. These include light-weight energy storage, high-sensitivity toxin sensors, artificial muscles, photoelectrochemical devices and components for fuel cells.