Fachgebiet Anorganische Chemie - Festkörper- und Materialchemie

19 Items

Recent Submissions
Metastable transition metal oxides, oxide nitrides, and nitrides

Lüdtke, Tobias Clemens (2017)

In the present cumulative work the successful synthesis of new compounds of transition metals, with focus on metastable oxides and oxide nitrides of the vanadium and chromium group, is reported. δ-TaON, a new polymorph of tantalum oxide nitride, besides the known β- and γ-phases, was extensively characterized by means of X-ray diffraction on powder samples, Rietveld refinement, anion compositi...

Diffusion pathways and activation energies in crystalline lithium-ion conductors

Wiedemann, Dennis ; Islam, Mazharul M. ; Bredow, Thomas ; Lerch, Martin (2017)

Geometric information about ion migration (diffusion pathways) and knowledge about the associated energy landscape (migration activation barriers) are essential cornerstones for a comprehensive understanding of lithium transport in solids. Although many lithium-ion conductors are discussed, developed, and already used as energy-storage materials, fundamental knowledge is often still lacking. In...

Band gap engineering: the role of anions

Anke, Björn (2017)

The degradation of harmful organic pollutants with the help of semiconductors is regarded as one of the crucial solutions for waste water treatment. The main disadvantage of extensively used photocatalysts such as SnO2, ZnO, and TiO2 is their activity under UV illumination due to their wide band gap (~ 3.2 eV). Therefore they can only absorb 5 – 7 % of the solar spectrum. In order to overcome t...

Unravelling ultraslow lithium-ion diffusion in γ-LiAlO2

Wiedemann, Dennis ; Nakhal, Suliman ; Rahn, Johanna ; Witt, Elena ; Islam, Mazharul M. ; Zander, Stefan ; Heitjans, Paul ; Schmidt, Harald ; Bredow, Thomas ; Wilkening, Martin ; Lerch, Martin (2016)

Lithium aluminum oxide (γ-LiAlO2) has been discussed and used for various applications, e.g., as electrode coating, membrane, or tritium breeder material. Although lithium-ion diffusion in this solid is essential for these purposes, it is still not sufficiently understood on the microscopic scale. Herein, we not only summarize and assess the available studies on diffusion in different crystalli...

Synthesis and structural characterization of semiconductors based on kesterites

Ritscher, Anna (2016)

The here-presented thesis provides detailed investigations on the structural characteristics of the chalcogenide Cu2ZnSnS4 (CZTS). This semiconductor material is a promising candidate for absorber layers in solar cells due to its desirable properties for thin film photovoltaic applications. Yet, compared to current used chalcopyrite-based devices, efficiencies are significantly lower. This coul...

Beiträge zur Nachhaltigkeit von chemischen Verfahren

Weidauer, Maik (2016)

Der Erste Teil der Arbeit beschäftigt sich mit der Synthese und Anwendung von Eisenkomplexen in der eisenkatalysierten oxidativen Kupplung von Magnesiumorganylen mit Hilfe von Distickstoffmonoxid als Oxidationsmittel. Als Plattform für die Komplexe dienten tripodale Liganden auf Basis von Tris((1H-pyrrol-2-yl)methyl)aminen und 2,2‘,2‘‘-Nitrilotris(methylen)trisphenolen. Im Zuge der Ligandensynt...

Lithium diffusion pathways in metastable ramsdellite-like Li2Ti3O7 from high-temperature neutron diffraction

Wiedemann, Dennis ; Nakhal, Suliman ; Franz, Alexandra ; Lerch, Martin (2016-10)

Ramsdellite-like Li2Ti3O7 is an excellent, strongly anisotropic lithium-ion conductor with various proposed applications in energy storage and lithium processing. Diffusion pathways have not yet been thoroughly studied, in spite of their importance for these purposes; even the precise crystal structure of this material is a subject of ongoing discussion. Herein, we use variable-temperature neut...

,, ... und ehrt mir ihre Kunst!“ – Evaluierung historischer und neuer Synthesewege zu 1,5-Dihydroxy-6-oxo-1,6-dihydropyridin-2-carbonsäure und 1,3-Dihydroxy-2-oxo-3-pyrrolin-4-carbonsäure

Wiedemann, Dennis ; Grohmann, Andreas (2009)

The historical and recent literature describing synthetical pathways to the title compds. is comprehensively summarized and evaluated. Routes via 2,5-dioxoadipic acid or 2,5-dihydroxymuconic acid as intermediates could not be followed reproducibly. 3-Hydroxy-2-oxo-2H-pyran-6-carboxylic acid and Et 3-hydroxy-2-oxo-3-pyrroline-4-carboxylate (I) were fully characterized by spectroscopic methods an...

Bond activation in iron(II) and nickel(II) complexes of polypodal phosphanes

Gentschow, Simon-Andreas ; Kohl, Stephan W. ; Bauer, Walter ; Heinemann, Frank W. ; Wiedemann, Dennis ; Grohmann, Andreas (2010)

A pyridine-derived tetraphosphane ligand (donor set: NP4) has been found to undergo remarkably specific C-P bond cleavage reactions, thereby producing a ligand with an NP3 donor set. The reaction may be reversed under suitable conditions, with regeneration of the original NP4 ligand. In order to investigate the mechanism of this reaction, the NP3 donor ligand C5H3N[CMe(CH2PMe2)2][CMe2(CH2PMe2)]...

(OC-6-13)-Difluoridooxidobis(propan-2-ol)(propan-2-olato)vanadium(V)

Kohl, Julia ; Wiedemann, Dennis (2013)

The distorted octahedral title complex, [V-V(C3H7O)(C3H8O)(2)F2O], was synthesized via ligand exchange at [(VO)-O-V(OiPr)(3)] with aqueous hydrogen fluoride in propan-2-ol and crystallized from (D) chloroform at 238 K after a few weeks. Crystal structure determination shows two C-1-symmetric moieties to be present in the asymmetric unit, forming infinite chains along [100] via hydrogen bonds. T...

Substituted bisphosphanylamines as ligands in gold(I) chemistry – synthesis and structures

Wiedemann, Dennis ; Gamer, Michael T. ; Roesky, Peter W. (2009)

Dimethyl 5-aminoisophthalate, which is a building block of amino-substituted tetralactam macrocycles, was used as ligand in gold(I) chemistry to form model complexes for macrocyclic gold compounds. Reaction of dimethyl 5-aminoisophthalate with chlorodiphenylphosphine gave the diphosphine compound dimethyl 5-[N,N-bis(diphenylphosphanyl)amino]isophthalate (dmbpaip). This compound can further be r...

3d-and 4d-metal(II) complexes of a tris(pyridyl)ethane-derived N-4 ligand – a structural study and reactivity remarks

Wiedemann, Dennis ; Grohmann, Andreas (2014)

A series of complexes of the new N-4 chelate ligand L (L = 1-{6-[1,1-bis(pyridin-2-yl) ethyl] pyridin-2-yl}-N, N-dimethylmethanamine) with intermediate to late divalent transition metal ions M was obtained by the reaction between L and the respective chloride salt or similar precursor in methanol: [MCl2L] (M = Mn, Fe, Co, Ni, Zn; Ru) and [CuClL]Cl. The stereochemical characteristics of the chel...

Thiocyanate anchors for salt-like iron(II) complexes on Au(111): promises and caveats

Stock, Philipp ; Erbe, Andreas ; Buck, Manfred ; Wiedemann, Dennis ; Ménard, Hervé ; Hörner, Gerald ; Grohmann, Andreas (2014)

The formation of self-assembled monolayers (SAMs) on Au(111) from solution has been investigated for two ionic iron(II) complexes of the type [Fe(L)](BF4)(2), where L is tripodal hexadentate and contains three thiocyanate anchor groups. The ligands (L1, L2; donor set: N-6) are obtained by Schiff base condensation of a tripodal triamine (L1: tris-(2-aminoethyl)amine, 'ten'; L2: 1,1',1 ''-trimeth...

Controlled ligand distortion and its consequences for structure, symmetry, conformation and spin-state preferences of iron(II) complexes

Kroll, Nicole ; Theilacker, Kolja ; Schoknecht, Marc ; Baabe, Dirk ; Wiedemann, Dennis ; Kaupp, Martin ; Grohmann, Andreas ; Hörner, Gerald (2015)

The ligand-field strength in metal complexes of polydentate ligands depends critically on how the ligand backbone places the donor atoms in three-dimensional space. Distortions from regular coordination geometries are often observed. In this work, we study the isolated effect of ligand-sphere distortion by means of two structurally related pentadentate ligands of identical donor set, in the sol...

Ternary transition-metal fluoride precursors for the fluorolytic sol-gel route: new insights into speciation and decomposition

Kohl, Julia ; Wiedemann, Dennis ; Troyanov, Sergej I. ; Palamidis, E. ; Lerch, Martin (2015)

The nanoscaled ternary transition-metal fluorides Li3MF6 (M = V, Fe, Mn) and Li2NiF4 are promising candidates for cathode materials in high-voltage lithium-ion batteries. The fluorolytic route to these compounds relies on thermal decomposition of a hitherto uncharacterised precursor mixture produced from acetylacetonates and hydrofluoric acid. By addition of pyridine, different cationic, electr...

The high-temperature transformation from 1T-to 3R-LixTiS2 (x=0.7, 0.9) as observed in situ with neutron powder diffraction

Wiedemann, Dennis ; Nakhal, Suliman ; Senyshyn, Anatoliy ; Bredow, Thomas ; Lerch, Martin (2015)

Layered titanium disulfide is used as lithium-ion intercalating electrode material in batteries. The room-temperature stable trigonal IT polymorphs of the intercalates LixTiS2(x <= 1) are widely-investigated. However, the rombohedral 3R polymorphs, being stable at higher temperatures for large x, are less well known. In this study, we report on the synthesis of phase-pure 1T-LixTiS2(x = 0.7, 0....

Lithium diffusion pathways in 3R-LixTiS2: a combined neutron diffraction and computational study

Wiedemann, Dennis ; Islam, Mazharul M. ; Nakhal, Suliman ; Senyshyn, Anatoliy ; Bredow, Thomas ; Lerch, Martin (2015)

Layered lithium transition-metal sulfides have long been discussed as early electrode materials for lithium-ion batteries. However, fundamental knowledge of lithium-ion migration in these solids is still lacking. In this study, we report on the diffusion dynamics in lithium-deficient high-temperature polymorphs of lithium titanium sulfides (3R-LixTiS2; x = 0.7, 0.9) as analyzed using powder neu...

LiBi3S5-A lithium bismuth sulfide with strong cation disorder

Nakhal, Suliman ; Wiedemann, Dennis ; Stanje, Bernhard ; Dolotko, Oleksandr ; Wilkening, Martin ; Lerch, Martin (2016)

Among chalcogenide semiconductors for thermoelectric applications, alkali-metal bismuth compounds occur in many complex compositions favorable for high performance. Although LiBi3S5 had been announced in 1977, the potential 1D lithium-ion conductor has hitherto eluded selective synthesis and structure determination. In this study, we present a solid-state route to phase-pure LiBi3S5 powder star...

Single-crystal neutron diffraction on gamma-LiAlO2: structure determination and estimation of lithium diffusion pathway

Wiedemann, Dennis ; Indris, Sylvio ; Meven, Martin ; Pedersen, Björn ; Boysen, Hans ; Uecker, Reinhard ; Heitjans, Paul ; Lerch, Martin (2016)

gamma-Lithium aluminum oxide is a paradigmatic example of an ultraslow lithium ion conductor. This characteristic plays a crucial role in its proposed and actual applications. Herein, we report on the outcome of single-crystal neutron diffraction studies at ambient and high temperature. Careful evaluation confirms the commonly assumed room-temperature structure as derived by powder neutron diff...