Carsten Streb | Universität Ulm (original) (raw)

Papers by Carsten Streb

Research paper thumbnail of Pyrene-Anderson-Modified CNTs as Anode Materials for Lithium-Ion Batteries

Chemistry (Weinheim an der Bergstrasse, Germany), Jan 5, 2015

An organo-functionalized polyoxometalate (POM)-pyrene hybrid (Py-Anderson) has been used for nonc... more An organo-functionalized polyoxometalate (POM)-pyrene hybrid (Py-Anderson) has been used for noncovalent functionalization of carbon nanotubes (CNTs) to give a Py-Anderson-CNT nanocomposite through π-π interactions. The as-synthesized nanocomposite was used as the anode material for lithium-ion batteries, and shows higher discharge capacities and better rate capacity and cycling stability than the individual components. When the current density was 0.5 mA cm(-2) , the nanocomposite exhibited an initial discharge capacity of 1898.5 mA h g(-1) and a high discharge capacity of 665.3 mA h g(-1) for up to 100 cycles. AC impedance spectroscopy provides insight into the electrochemical properties and the charge-transfer mechanism of the Py-Anderson-CNTs electrode.

Research paper thumbnail of Novel phenanthroline–diaryldiazadiene ligands with heteroditopic coordination spheres

Dalton Trans., 2015

1,10-Phenanthroline-5,6-diaryldiazadienes are key structures for the development of novel heterod... more 1,10-Phenanthroline-5,6-diaryldiazadienes are key structures for the development of novel heterodinuclear photocatalysts and for the construction of extended heterocycles of potential biological use. Herein, the first examples of this compound family are presented together with a wide range of initial reactivity studies. Synthetic strategies are presented to access the two first derivatives of the ligand and to accomplish subsequent metal coordination to the phenanthroline sphere.

Research paper thumbnail of Reversible photodimerization of coumarin-modified Wells–Dawson anions

J. Mater. Chem. C, 2015

ABSTRACT Organo-modified photo-sensitive polyoxometalates (POMs) are a unique class of functional... more ABSTRACT Organo-modified photo-sensitive polyoxometalates (POMs) are a unique class of functional molecular materials. Here we show how reversible light-driven dimerization in organo-functionalized POMs can be achieved. To this end, the vanadium-substituted Wells-Dawson cluster [P2V3W15O62]9- was modified with a coumarin-based derivative to give the new organic-inorganic hybrid (nBu4N)4H2[C12H9O4NHC(CH2O)3P2W15V3O59]. Upon photo-irradiation, the compound undergoes reversible photodimerization which was characterized using various spectroscopic methods including FT-IR, UV-Vis, DLS (dynamic light scattering), 1H NMR, COSY NMR and ESI-MS. These results are in good agreement with the formation of dimer species. In addition, XPS and EPR analyses of the photo-irradiation product indicate that V5+ is partially reduced to V4+, while W6+ is not affected, suggesting that coupled photo-dimerization and selective redox-switching might become possible.

Research paper thumbnail of Template-dependent photochemical reactivity of molecular metal oxides

Chemistry (Weinheim an der Bergstrasse, Germany), Jan 8, 2015

A combined experimental and theoretical study shows that the photooxidative activity of two isost... more A combined experimental and theoretical study shows that the photooxidative activity of two isostructural metal oxide clusters depends on their internal templates. To this end, two halide-templated bismuth vanadium oxide clusters [X(Bi(dmso)3 )2 V12 O33 ](-) (X=Cl(-) , Br(-) ) are reported and fully characterized. The two clusters show similar absorption features and illustrate that bismuth incorporation results in increased visible-light absorption. Significantly higher photooxidative activity is observed for the bromide-templated cluster compared with the chloride-templated one. Detailed photophysical assays and complementary DFT calculations suggest that the more efficient triplet excited state formation in the Br(-) -containing cluster is the decisive step in the photocatalysis and is due to the heavy-atom effect of the bromide. This concept can therefore open new pathways towards the optimization of photocatalytic activity in metal oxide clusters.

Research paper thumbnail of Controlled Reactivity Tuning of Metal-Functionalized Vanadium Oxide Clusters

Chemistry (Weinheim an der Bergstrasse, Germany), Jan 7, 2015

Controlling the assembly and functionalization of molecular metal oxides [Mx Oy ](n-) (M=Mo, W, V... more Controlling the assembly and functionalization of molecular metal oxides [Mx Oy ](n-) (M=Mo, W, V) allows the targeted design of functional molecular materials. While general methods exist that enable the predetermined functionalization of tungstates and molybdates, no such routes are available for molecular vanadium oxides. Controlled design of polyoxovanadates, however, would provide highly active materials for energy conversion, (photo-) catalysis, molecular magnetism, and materials science. To this end, a new approach has been developed that allows the reactivity tuning of vanadium oxide clusters by selective metal functionalization. Organic, hydrogen-bonding cations, for example, dimethylammonium are used as molecular placeholders to block metal binding sites within vanadate cluster shells. Stepwise replacement of the placeholder cations with reactive metal cations gives mono- and difunctionalized clusters. Initial reactivity studies illustrate the tunability of the magnetic, r...

Research paper thumbnail of Covalent Attachment of Anderson-Type Polyoxometalates to Single-Walled Carbon Nanotubes Gives Enhanced Performance Electrodes for Lithium Ion Batteries

Chemistry (Weinheim an der Bergstrasse, Germany), Jan 12, 2015

Single-walled carbon nanotubes (SWNTs) covalently functionalized with redox-active organo-modifie... more Single-walled carbon nanotubes (SWNTs) covalently functionalized with redox-active organo-modified polyoxometalate (POM) clusters have been synthesized and employed as electrode materials in lithium ion batteries. The Anderson cluster [MnMo6 O24 ](9-) is functionalized with Tris (NH2 C(CH2 OH)3 ) moieties, giving the new organic-inorganic hybrid [N(nC4 H9 )4 ]3 [MnMo6 O18 {(OCH2 )3 CNH2 }2 ]. The compound is then covalently attached to carboxylic acid-functionalized SWNTs by amide bond formation and the stability of this nanocomposite is confirmed by various spectroscopic methods. Electrochemical analyses show that the nanocomposite displays improved performance as an anode material in lithium ion batteries compared with the individual components, that is, SWNTs and/or Anderson clusters. High discharge capacities of up to 932 mAh g(-1) at a current density of 0.5 mA cm(-2) can be observed, together with high long-term cycling stability and decreased electrochemical impedance. Chemis...

Research paper thumbnail of Polyoxometalate – conductive polymer composites for energy conversion, energy storage and nanostructured sensors

Dalton Trans., 2015

The exchange of electric charges between a chemical reaction centre and an external electrical ci... more 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.

Research paper thumbnail of Thermochromic and solvatochromic properties of CoCl2 solution

The paper present detailed spectrophotometric studies of thermochromic and solvatochromic propert... more The paper present detailed spectrophotometric studies of thermochromic and solvatochromic properties of solutions of cobalt chloride. The solution exhibits absorbance changes in the visible spectrum in dependence of the temperature and polarity of the solvent used. The ...

Research paper thumbnail of Polyoxometalate-functionalized nanocarbon materials for energy conversion, energy storage and sensor systems

ABSTRACT Composites based on polyoxometalates (POMs) and nanostructured carbon such as carbon nan... more ABSTRACT Composites based on polyoxometalates (POMs) and nanostructured carbon such as carbon nanotubes (CNTs) or graphene have attracted widespread attention as they combine the unique chemical reactivity of POMs with the unparalleled electronic properties of nanocarbons. The exceptional properties of these composites have been employed in catalysis, energy conversion and storage, molecular sensors and electronics. Herein, we summarize the latest progress in POM/CNT and POM/graphene nanocomposites with a focus on energy materials for water splitting and fuel cells, composite electrode materials for batteries and supercapacitors as well as composites for sensor systems. Current applications are critically assessed and promising future target systems are discussed.

Research paper thumbnail of Innentitelbild: Polyoxometallat-basierte ionische Flüssigkeiten als selbstreparierender Säure-Korrosionsschutz (Angew. Chem. 49/2014)

Angewandte Chemie, 2014

ABSTRACT Korrosion ist ein weltweites Problem, vor allem für Metalle. Hier wird gezeigt, wie Meta... more ABSTRACT Korrosion ist ein weltweites Problem, vor allem für Metalle. Hier wird gezeigt, wie Metalle durch hydrophobe Polxoxometallat-basierte ionische Flüssigkeiten (POM-ILs) leicht vor Säurekorrosion geschützt werden können. Dafür wurden Cu-Plättchen mit bei Raumtemperatur flüssigen POM-Ils auf Basis von Übergangsmetall-funktionalisierten Keggin-Anionen [SiW11O39M(H2O)]n− (M=CuII, FeIII) und quartären Alkylammonium-Kationen (CnH2n+1)4N+ (n=7–8) beschichtet. Die Korrosionsbeständigkeit gegen Säuredämpfe und in einem simulierten sauren Regen konnte im Vergleich zu Beschichtungen auf Basis kommerzieller ILs oder fester Polyoxometallate signifikant verbessert werden. Schäden durch mechanische Beanspruchung der POM-IL-Beschichtung verheilen binnen einer Minute unter vollständiger Regenerierung der Schutzeigenschaften. Die Beschichtung lässt sich leicht durch Waschen mit organischen Lösungsmitteln entfernen.

Research paper thumbnail of POLYOXOMETALATE-IONIC LIQUIDS (POM-ILs)–THE ULTIMATE SOFT POLYOXOMETALATES? A CRITICAL PERSPECTIVE

Journal of Molecular and Engineering Materials, 2014

Research paper thumbnail of Polyoxometallat-basierte ionische Flüssigkeiten als selbstreparierender Säure-Korrosionsschutz

Angewandte Chemie, 2014

ABSTRACT Korrosion ist ein weltweites Problem, vor allem für Metalle. Hier wird gezeigt, wie Meta... more ABSTRACT Korrosion ist ein weltweites Problem, vor allem für Metalle. Hier wird gezeigt, wie Metalle durch hydrophobe Polxoxometallat-basierte ionische Flüssigkeiten (POM-ILs) leicht vor Säurekorrosion geschützt werden können. Dafür wurden Cu-Plättchen mit bei Raumtemperatur flüssigen POM-Ils auf Basis von Übergangsmetall-funktionalisierten Keggin-Anionen [SiW11O39M(H2O)]n− (M=CuII, FeIII) und quartären Alkylammonium-Kationen (CnH2n+1)4N+ (n=7–8) beschichtet. Die Korrosionsbeständigkeit gegen Säuredämpfe und in einem simulierten sauren Regen konnte im Vergleich zu Beschichtungen auf Basis kommerzieller ILs oder fester Polyoxometallate signifikant verbessert werden. Schäden durch mechanische Beanspruchung der POM-IL-Beschichtung verheilen binnen einer Minute unter vollständiger Regenerierung der Schutzeigenschaften. Die Beschichtung lässt sich leicht durch Waschen mit organischen Lösungsmitteln entfernen.

Research paper thumbnail of Molecular Metal Oxides for Energy Conversion and Energy Storage

Pignataro/Discovering the Future of Molecular Sciences, 2014

ABSTRACT

Research paper thumbnail of Cluster-controlled dimerisation in supramolecular ruthenium photosensitizer-polyoxometalate systems

Dalton transactions (Cambridge, England : 2003), Jan 7, 2015

A supramolecular reaction system is reported where a labile molecular metal oxide cluster enables... more A supramolecular reaction system is reported where a labile molecular metal oxide cluster enables the unprecedented dimerisation of ruthenium photosensitizers [Ru(L)2(tmbiH2)](2+) (L = 4,4'-di-tert-butyl-2,2'-bipyridine (1a) or 2,2'-bipyridine (1b); tmbiH2 = 5,5',6,6'-tetramethyl-2,2'-bibenzimidazole). In the presence of [Mo8O26](4-) clusters (2) the dimerisation is triggered by the in situ conversion of [Mo8O26](4-) to [Mo6O19](2-) which results in the release of hydroxide ions. Simultaneous deprotonation of the pH-sensitive tmbiH2-ligands starts the dimerisation, resulting in the formation of the dinuclear complex [(Ru(L)2)2(tmbi)](2+) (L = 4,4'-di-tert-butyl-2,2'-bipyridine (3) or 2,2'-bipyridine (4)). The dimerisation reaction can be suppressed when 2 is replaced by a stable polyoxomolybdate cluster, [Mo5O15(PhPO3)2](4-) (5) and the reaction between 1a and 5 leads to the formation of hydrogen-bonded supramolecular aggregates 6. The solution an...

Research paper thumbnail of Polyoxometalate ionic liquids as self-repairing acid-resistant corrosion protection

Angewandte Chemie (International ed. in English), 2014

Corrosion is a global problem for any metallic structure or material. Herein we show how metals c... more Corrosion is a global problem for any metallic structure or material. Herein we show how metals can easily be protected against acid corrosion using hydrophobic polyoxometalate-based ionic liquids (POM-ILs). Copper metal disks were coated with room-temperature POM-ILs composed of transition-metal functionalized Keggin anions [SiW11 O39 TM(H2 O)](n-) (TM=Cu(II) , Fe(III) ) and quaternary alkylammonium cations (Cn H2 n+1 )4 N(+) (n=7-8). The corrosion resistance against acetic acid vapors and simulated "acid rain" was significantly improved compared with commercial ionic liquids or solid polyoxometalate coatings. Mechanical damage to the POM-IL coating is self-repaired in less than one minute with full retention of the acid protection properties. The coating can easily be removed and recovered by rinsing with organic solvents.

Research paper thumbnail of Photocatalytic reactivity tuning by heterometal and addenda metal variation in Lindqvist polyoxometalates

Dalton transactions (Cambridge, England : 2003), Jan 7, 2014

A systematic study into the effects of metal substitution on the visible-light photocatalytic act... more A systematic study into the effects of metal substitution on the visible-light photocatalytic activity of prototype metal oxide cluster anions is presented. Four isostructural Lindqvist clusters [V(x)M(6-x)O19]((2+x)-) (M = W, Mo, x = 1, 2) with photooxidative activity in the visible range are reported. It is shown that the photooxidative performance correlates with the number of vanadium atoms in the cluster. Further, two divergent reaction mechanisms are observed depending on the type of addenda metal (i.e. Mo or W) used. When comparing the reactivity under aerated vs. de-aerated conditions, it was found that molybdate-based clusters show significantly increased reaction rates in the absence of oxygen; in contrast, marginally reduced reaction rates were observed for the tungstate-based species under de-aerated conditions. Wavelength-dependent quantum efficiency studies provide insight into the visible-light reactivity of all four species. Radical scavenging experiments suggest tha...

Research paper thumbnail of A new class of homogeneous visible-light photocatalysts: molecular cerium vanadium oxide clusters

Chemistry (Weinheim an der Bergstrasse, Germany), Jan 28, 2014

The first systematic access to molecular cerium vanadium oxides is presented. A family of structu... more The first systematic access to molecular cerium vanadium oxides is presented. A family of structurally related, di-cerium-functionalized vanadium oxide clusters and their use as visible-light-driven photooxidation catalysts is reported. Comparative analyses show that photocatalytic activity is controlled by the cluster architecture. Increased photoreactivity of the cerium vanadium oxides in the visible range compared with nonfunctionalized vanadates is observed. Based on the recent discovery of the first molecular cerium vanadate cluster, (nBu4 N)2 [(Ce(dmso)3 )2 V12 O33 Cl]⋅2 DMSO (1), two new di-cerium-containing vanadium oxide clusters [(Ce(dmso)4 )2 V11 O30 Cl]⋅DMSO (2) and [(Ce(nmp)4 )2 V12 O32 Cl]⋅NMP⋅Me2 CO (3; NMP=N-methyl-2-pyrrolidone) were obtained by using a novel fragmentation and reassembly route. Pentagonal building units {(V)M5 } (M=V, Ce) reminiscent of "Müller-type" pentagons are observed in 2 and 3. Compounds 1-3 feature high visible-light photooxidative...

Research paper thumbnail of Inside Cover: Polyoxometalate Ionic Liquids as Self-Repairing Acid-Resistant Corrosion Protection (Angew. Chem. Int. Ed. 49/2014)

Angewandte Chemie International Edition, 2014

Research paper thumbnail of A Molecular Placeholder Strategy To Access a Family of Transition-Metal-Functionalized Vanadium Oxide Clusters

Chemistry - A European Journal, 2014

Systematic access to metal-functionalized polyoxometalates has thus far been limited to lacunary ... more Systematic access to metal-functionalized polyoxometalates has thus far been limited to lacunary tungsten oxide and molybdenum oxide clusters. The first controlled, stepwise bottom-up assembly route to metal-functionalized molecular vanadium oxides is now presented. A di-vacant vanadate cluster with two metal binding sites, (DMA)2[V12O32Cl](3-) (DMA = dimethylammonium) is formed spontaneously in solution and characterized by single-crystal X-ray diffraction, ESI mass spectrometry, (51)V NMR spectroscopy, and elemental analyses. In the cluster, the metal binding sites are selectively blocked by hydrogen-bonded DMA placeholder cations. Reaction of the cluster with transition metals TM (Fe(3+), Co(2+), Cu(2+), Zn(2+)) gives access to mono-functionalized vanadate clusters (DMA)[{TM(L)}V12O32Cl](n-) (L = ligand). Metal binding is accomplished by significant distortions of the vanadium oxide framework reminiscent of a pincer movement. Cluster stability under technologically relevant conditions in the solid-state and solution is demonstrated.

Research paper thumbnail of Visible light photooxidative performance of a high-nuclearity molecular bismuth vanadium oxide cluster

Beilstein Journal of Nanotechnology, 2014

The visible light photooxidative performance of a new high-nuclearity molecular bismuth vanadium ... more The visible light photooxidative performance of a new high-nuclearity molecular bismuth vanadium oxide cluster, H3[{Bi(dmso)3}4V13O40], is reported. Photocatalytic activity studies show faster reaction kinetics under anaerobic conditions, suggesting an oxygen-dependent quenching of the photoexcited cluster species. Further mechanistic analysis shows that the reaction proceeds via the intermediate formation of hydroxyl radicals which act as oxidant. Trapping experiments using ethanol as a hydroxyl radical scavenger show significantly decreased photocatalytic substrate oxidation in the presence of EtOH. Photocatalytic performance analyses using monochromatic visible light irradiation show that the quantum efficiency Φ for indigo photooxidation is strongly dependent on the irradiation wavelength, with higher quantum efficiencies being observed at shorter wavelengths (Φ395nm ca. 15%). Recycling tests show that the compound can be employed as homogeneous photooxidation catalyst multiple times without loss of catalytic activity. High turnover numbers (TON ca. 1200) and turnover frequencies up to TOF ca. 3.44 min(-1) are observed, illustrating the practical applicability of the cluster species.

Research paper thumbnail of Pyrene-Anderson-Modified CNTs as Anode Materials for Lithium-Ion Batteries

Chemistry (Weinheim an der Bergstrasse, Germany), Jan 5, 2015

An organo-functionalized polyoxometalate (POM)-pyrene hybrid (Py-Anderson) has been used for nonc... more An organo-functionalized polyoxometalate (POM)-pyrene hybrid (Py-Anderson) has been used for noncovalent functionalization of carbon nanotubes (CNTs) to give a Py-Anderson-CNT nanocomposite through π-π interactions. The as-synthesized nanocomposite was used as the anode material for lithium-ion batteries, and shows higher discharge capacities and better rate capacity and cycling stability than the individual components. When the current density was 0.5 mA cm(-2) , the nanocomposite exhibited an initial discharge capacity of 1898.5 mA h g(-1) and a high discharge capacity of 665.3 mA h g(-1) for up to 100 cycles. AC impedance spectroscopy provides insight into the electrochemical properties and the charge-transfer mechanism of the Py-Anderson-CNTs electrode.

Research paper thumbnail of Novel phenanthroline–diaryldiazadiene ligands with heteroditopic coordination spheres

Dalton Trans., 2015

1,10-Phenanthroline-5,6-diaryldiazadienes are key structures for the development of novel heterod... more 1,10-Phenanthroline-5,6-diaryldiazadienes are key structures for the development of novel heterodinuclear photocatalysts and for the construction of extended heterocycles of potential biological use. Herein, the first examples of this compound family are presented together with a wide range of initial reactivity studies. Synthetic strategies are presented to access the two first derivatives of the ligand and to accomplish subsequent metal coordination to the phenanthroline sphere.

Research paper thumbnail of Reversible photodimerization of coumarin-modified Wells–Dawson anions

J. Mater. Chem. C, 2015

ABSTRACT Organo-modified photo-sensitive polyoxometalates (POMs) are a unique class of functional... more ABSTRACT Organo-modified photo-sensitive polyoxometalates (POMs) are a unique class of functional molecular materials. Here we show how reversible light-driven dimerization in organo-functionalized POMs can be achieved. To this end, the vanadium-substituted Wells-Dawson cluster [P2V3W15O62]9- was modified with a coumarin-based derivative to give the new organic-inorganic hybrid (nBu4N)4H2[C12H9O4NHC(CH2O)3P2W15V3O59]. Upon photo-irradiation, the compound undergoes reversible photodimerization which was characterized using various spectroscopic methods including FT-IR, UV-Vis, DLS (dynamic light scattering), 1H NMR, COSY NMR and ESI-MS. These results are in good agreement with the formation of dimer species. In addition, XPS and EPR analyses of the photo-irradiation product indicate that V5+ is partially reduced to V4+, while W6+ is not affected, suggesting that coupled photo-dimerization and selective redox-switching might become possible.

Research paper thumbnail of Template-dependent photochemical reactivity of molecular metal oxides

Chemistry (Weinheim an der Bergstrasse, Germany), Jan 8, 2015

A combined experimental and theoretical study shows that the photooxidative activity of two isost... more A combined experimental and theoretical study shows that the photooxidative activity of two isostructural metal oxide clusters depends on their internal templates. To this end, two halide-templated bismuth vanadium oxide clusters [X(Bi(dmso)3 )2 V12 O33 ](-) (X=Cl(-) , Br(-) ) are reported and fully characterized. The two clusters show similar absorption features and illustrate that bismuth incorporation results in increased visible-light absorption. Significantly higher photooxidative activity is observed for the bromide-templated cluster compared with the chloride-templated one. Detailed photophysical assays and complementary DFT calculations suggest that the more efficient triplet excited state formation in the Br(-) -containing cluster is the decisive step in the photocatalysis and is due to the heavy-atom effect of the bromide. This concept can therefore open new pathways towards the optimization of photocatalytic activity in metal oxide clusters.

Research paper thumbnail of Controlled Reactivity Tuning of Metal-Functionalized Vanadium Oxide Clusters

Chemistry (Weinheim an der Bergstrasse, Germany), Jan 7, 2015

Controlling the assembly and functionalization of molecular metal oxides [Mx Oy ](n-) (M=Mo, W, V... more Controlling the assembly and functionalization of molecular metal oxides [Mx Oy ](n-) (M=Mo, W, V) allows the targeted design of functional molecular materials. While general methods exist that enable the predetermined functionalization of tungstates and molybdates, no such routes are available for molecular vanadium oxides. Controlled design of polyoxovanadates, however, would provide highly active materials for energy conversion, (photo-) catalysis, molecular magnetism, and materials science. To this end, a new approach has been developed that allows the reactivity tuning of vanadium oxide clusters by selective metal functionalization. Organic, hydrogen-bonding cations, for example, dimethylammonium are used as molecular placeholders to block metal binding sites within vanadate cluster shells. Stepwise replacement of the placeholder cations with reactive metal cations gives mono- and difunctionalized clusters. Initial reactivity studies illustrate the tunability of the magnetic, r...

Research paper thumbnail of Covalent Attachment of Anderson-Type Polyoxometalates to Single-Walled Carbon Nanotubes Gives Enhanced Performance Electrodes for Lithium Ion Batteries

Chemistry (Weinheim an der Bergstrasse, Germany), Jan 12, 2015

Single-walled carbon nanotubes (SWNTs) covalently functionalized with redox-active organo-modifie... more Single-walled carbon nanotubes (SWNTs) covalently functionalized with redox-active organo-modified polyoxometalate (POM) clusters have been synthesized and employed as electrode materials in lithium ion batteries. The Anderson cluster [MnMo6 O24 ](9-) is functionalized with Tris (NH2 C(CH2 OH)3 ) moieties, giving the new organic-inorganic hybrid [N(nC4 H9 )4 ]3 [MnMo6 O18 {(OCH2 )3 CNH2 }2 ]. The compound is then covalently attached to carboxylic acid-functionalized SWNTs by amide bond formation and the stability of this nanocomposite is confirmed by various spectroscopic methods. Electrochemical analyses show that the nanocomposite displays improved performance as an anode material in lithium ion batteries compared with the individual components, that is, SWNTs and/or Anderson clusters. High discharge capacities of up to 932 mAh g(-1) at a current density of 0.5 mA cm(-2) can be observed, together with high long-term cycling stability and decreased electrochemical impedance. Chemis...

Research paper thumbnail of Polyoxometalate – conductive polymer composites for energy conversion, energy storage and nanostructured sensors

Dalton Trans., 2015

The exchange of electric charges between a chemical reaction centre and an external electrical ci... more 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.

Research paper thumbnail of Thermochromic and solvatochromic properties of CoCl2 solution

The paper present detailed spectrophotometric studies of thermochromic and solvatochromic propert... more The paper present detailed spectrophotometric studies of thermochromic and solvatochromic properties of solutions of cobalt chloride. The solution exhibits absorbance changes in the visible spectrum in dependence of the temperature and polarity of the solvent used. The ...

Research paper thumbnail of Polyoxometalate-functionalized nanocarbon materials for energy conversion, energy storage and sensor systems

ABSTRACT Composites based on polyoxometalates (POMs) and nanostructured carbon such as carbon nan... more ABSTRACT Composites based on polyoxometalates (POMs) and nanostructured carbon such as carbon nanotubes (CNTs) or graphene have attracted widespread attention as they combine the unique chemical reactivity of POMs with the unparalleled electronic properties of nanocarbons. The exceptional properties of these composites have been employed in catalysis, energy conversion and storage, molecular sensors and electronics. Herein, we summarize the latest progress in POM/CNT and POM/graphene nanocomposites with a focus on energy materials for water splitting and fuel cells, composite electrode materials for batteries and supercapacitors as well as composites for sensor systems. Current applications are critically assessed and promising future target systems are discussed.

Research paper thumbnail of Innentitelbild: Polyoxometallat-basierte ionische Flüssigkeiten als selbstreparierender Säure-Korrosionsschutz (Angew. Chem. 49/2014)

Angewandte Chemie, 2014

ABSTRACT Korrosion ist ein weltweites Problem, vor allem für Metalle. Hier wird gezeigt, wie Meta... more ABSTRACT Korrosion ist ein weltweites Problem, vor allem für Metalle. Hier wird gezeigt, wie Metalle durch hydrophobe Polxoxometallat-basierte ionische Flüssigkeiten (POM-ILs) leicht vor Säurekorrosion geschützt werden können. Dafür wurden Cu-Plättchen mit bei Raumtemperatur flüssigen POM-Ils auf Basis von Übergangsmetall-funktionalisierten Keggin-Anionen [SiW11O39M(H2O)]n− (M=CuII, FeIII) und quartären Alkylammonium-Kationen (CnH2n+1)4N+ (n=7–8) beschichtet. Die Korrosionsbeständigkeit gegen Säuredämpfe und in einem simulierten sauren Regen konnte im Vergleich zu Beschichtungen auf Basis kommerzieller ILs oder fester Polyoxometallate signifikant verbessert werden. Schäden durch mechanische Beanspruchung der POM-IL-Beschichtung verheilen binnen einer Minute unter vollständiger Regenerierung der Schutzeigenschaften. Die Beschichtung lässt sich leicht durch Waschen mit organischen Lösungsmitteln entfernen.

Research paper thumbnail of POLYOXOMETALATE-IONIC LIQUIDS (POM-ILs)–THE ULTIMATE SOFT POLYOXOMETALATES? A CRITICAL PERSPECTIVE

Journal of Molecular and Engineering Materials, 2014

Research paper thumbnail of Polyoxometallat-basierte ionische Flüssigkeiten als selbstreparierender Säure-Korrosionsschutz

Angewandte Chemie, 2014

ABSTRACT Korrosion ist ein weltweites Problem, vor allem für Metalle. Hier wird gezeigt, wie Meta... more ABSTRACT Korrosion ist ein weltweites Problem, vor allem für Metalle. Hier wird gezeigt, wie Metalle durch hydrophobe Polxoxometallat-basierte ionische Flüssigkeiten (POM-ILs) leicht vor Säurekorrosion geschützt werden können. Dafür wurden Cu-Plättchen mit bei Raumtemperatur flüssigen POM-Ils auf Basis von Übergangsmetall-funktionalisierten Keggin-Anionen [SiW11O39M(H2O)]n− (M=CuII, FeIII) und quartären Alkylammonium-Kationen (CnH2n+1)4N+ (n=7–8) beschichtet. Die Korrosionsbeständigkeit gegen Säuredämpfe und in einem simulierten sauren Regen konnte im Vergleich zu Beschichtungen auf Basis kommerzieller ILs oder fester Polyoxometallate signifikant verbessert werden. Schäden durch mechanische Beanspruchung der POM-IL-Beschichtung verheilen binnen einer Minute unter vollständiger Regenerierung der Schutzeigenschaften. Die Beschichtung lässt sich leicht durch Waschen mit organischen Lösungsmitteln entfernen.

Research paper thumbnail of Molecular Metal Oxides for Energy Conversion and Energy Storage

Pignataro/Discovering the Future of Molecular Sciences, 2014

ABSTRACT

Research paper thumbnail of Cluster-controlled dimerisation in supramolecular ruthenium photosensitizer-polyoxometalate systems

Dalton transactions (Cambridge, England : 2003), Jan 7, 2015

A supramolecular reaction system is reported where a labile molecular metal oxide cluster enables... more A supramolecular reaction system is reported where a labile molecular metal oxide cluster enables the unprecedented dimerisation of ruthenium photosensitizers [Ru(L)2(tmbiH2)](2+) (L = 4,4'-di-tert-butyl-2,2'-bipyridine (1a) or 2,2'-bipyridine (1b); tmbiH2 = 5,5',6,6'-tetramethyl-2,2'-bibenzimidazole). In the presence of [Mo8O26](4-) clusters (2) the dimerisation is triggered by the in situ conversion of [Mo8O26](4-) to [Mo6O19](2-) which results in the release of hydroxide ions. Simultaneous deprotonation of the pH-sensitive tmbiH2-ligands starts the dimerisation, resulting in the formation of the dinuclear complex [(Ru(L)2)2(tmbi)](2+) (L = 4,4'-di-tert-butyl-2,2'-bipyridine (3) or 2,2'-bipyridine (4)). The dimerisation reaction can be suppressed when 2 is replaced by a stable polyoxomolybdate cluster, [Mo5O15(PhPO3)2](4-) (5) and the reaction between 1a and 5 leads to the formation of hydrogen-bonded supramolecular aggregates 6. The solution an...

Research paper thumbnail of Polyoxometalate ionic liquids as self-repairing acid-resistant corrosion protection

Angewandte Chemie (International ed. in English), 2014

Corrosion is a global problem for any metallic structure or material. Herein we show how metals c... more Corrosion is a global problem for any metallic structure or material. Herein we show how metals can easily be protected against acid corrosion using hydrophobic polyoxometalate-based ionic liquids (POM-ILs). Copper metal disks were coated with room-temperature POM-ILs composed of transition-metal functionalized Keggin anions [SiW11 O39 TM(H2 O)](n-) (TM=Cu(II) , Fe(III) ) and quaternary alkylammonium cations (Cn H2 n+1 )4 N(+) (n=7-8). The corrosion resistance against acetic acid vapors and simulated "acid rain" was significantly improved compared with commercial ionic liquids or solid polyoxometalate coatings. Mechanical damage to the POM-IL coating is self-repaired in less than one minute with full retention of the acid protection properties. The coating can easily be removed and recovered by rinsing with organic solvents.

Research paper thumbnail of Photocatalytic reactivity tuning by heterometal and addenda metal variation in Lindqvist polyoxometalates

Dalton transactions (Cambridge, England : 2003), Jan 7, 2014

A systematic study into the effects of metal substitution on the visible-light photocatalytic act... more A systematic study into the effects of metal substitution on the visible-light photocatalytic activity of prototype metal oxide cluster anions is presented. Four isostructural Lindqvist clusters [V(x)M(6-x)O19]((2+x)-) (M = W, Mo, x = 1, 2) with photooxidative activity in the visible range are reported. It is shown that the photooxidative performance correlates with the number of vanadium atoms in the cluster. Further, two divergent reaction mechanisms are observed depending on the type of addenda metal (i.e. Mo or W) used. When comparing the reactivity under aerated vs. de-aerated conditions, it was found that molybdate-based clusters show significantly increased reaction rates in the absence of oxygen; in contrast, marginally reduced reaction rates were observed for the tungstate-based species under de-aerated conditions. Wavelength-dependent quantum efficiency studies provide insight into the visible-light reactivity of all four species. Radical scavenging experiments suggest tha...

Research paper thumbnail of A new class of homogeneous visible-light photocatalysts: molecular cerium vanadium oxide clusters

Chemistry (Weinheim an der Bergstrasse, Germany), Jan 28, 2014

The first systematic access to molecular cerium vanadium oxides is presented. A family of structu... more The first systematic access to molecular cerium vanadium oxides is presented. A family of structurally related, di-cerium-functionalized vanadium oxide clusters and their use as visible-light-driven photooxidation catalysts is reported. Comparative analyses show that photocatalytic activity is controlled by the cluster architecture. Increased photoreactivity of the cerium vanadium oxides in the visible range compared with nonfunctionalized vanadates is observed. Based on the recent discovery of the first molecular cerium vanadate cluster, (nBu4 N)2 [(Ce(dmso)3 )2 V12 O33 Cl]⋅2 DMSO (1), two new di-cerium-containing vanadium oxide clusters [(Ce(dmso)4 )2 V11 O30 Cl]⋅DMSO (2) and [(Ce(nmp)4 )2 V12 O32 Cl]⋅NMP⋅Me2 CO (3; NMP=N-methyl-2-pyrrolidone) were obtained by using a novel fragmentation and reassembly route. Pentagonal building units {(V)M5 } (M=V, Ce) reminiscent of "Müller-type" pentagons are observed in 2 and 3. Compounds 1-3 feature high visible-light photooxidative...

Research paper thumbnail of Inside Cover: Polyoxometalate Ionic Liquids as Self-Repairing Acid-Resistant Corrosion Protection (Angew. Chem. Int. Ed. 49/2014)

Angewandte Chemie International Edition, 2014

Research paper thumbnail of A Molecular Placeholder Strategy To Access a Family of Transition-Metal-Functionalized Vanadium Oxide Clusters

Chemistry - A European Journal, 2014

Systematic access to metal-functionalized polyoxometalates has thus far been limited to lacunary ... more Systematic access to metal-functionalized polyoxometalates has thus far been limited to lacunary tungsten oxide and molybdenum oxide clusters. The first controlled, stepwise bottom-up assembly route to metal-functionalized molecular vanadium oxides is now presented. A di-vacant vanadate cluster with two metal binding sites, (DMA)2[V12O32Cl](3-) (DMA = dimethylammonium) is formed spontaneously in solution and characterized by single-crystal X-ray diffraction, ESI mass spectrometry, (51)V NMR spectroscopy, and elemental analyses. In the cluster, the metal binding sites are selectively blocked by hydrogen-bonded DMA placeholder cations. Reaction of the cluster with transition metals TM (Fe(3+), Co(2+), Cu(2+), Zn(2+)) gives access to mono-functionalized vanadate clusters (DMA)[{TM(L)}V12O32Cl](n-) (L = ligand). Metal binding is accomplished by significant distortions of the vanadium oxide framework reminiscent of a pincer movement. Cluster stability under technologically relevant conditions in the solid-state and solution is demonstrated.

Research paper thumbnail of Visible light photooxidative performance of a high-nuclearity molecular bismuth vanadium oxide cluster

Beilstein Journal of Nanotechnology, 2014

The visible light photooxidative performance of a new high-nuclearity molecular bismuth vanadium ... more The visible light photooxidative performance of a new high-nuclearity molecular bismuth vanadium oxide cluster, H3[{Bi(dmso)3}4V13O40], is reported. Photocatalytic activity studies show faster reaction kinetics under anaerobic conditions, suggesting an oxygen-dependent quenching of the photoexcited cluster species. Further mechanistic analysis shows that the reaction proceeds via the intermediate formation of hydroxyl radicals which act as oxidant. Trapping experiments using ethanol as a hydroxyl radical scavenger show significantly decreased photocatalytic substrate oxidation in the presence of EtOH. Photocatalytic performance analyses using monochromatic visible light irradiation show that the quantum efficiency Φ for indigo photooxidation is strongly dependent on the irradiation wavelength, with higher quantum efficiencies being observed at shorter wavelengths (Φ395nm ca. 15%). Recycling tests show that the compound can be employed as homogeneous photooxidation catalyst multiple times without loss of catalytic activity. High turnover numbers (TON ca. 1200) and turnover frequencies up to TOF ca. 3.44 min(-1) are observed, illustrating the practical applicability of the cluster species.