Gudrun Auffermann

SrN and SrN2: Diazenides by Synthesis under High N2-Pressure

Nitride and/or diazenide ions in the octahedral holes of nearly close-packed arrangements of Sr2+ ions characterize the new compounds described herein. They were obtained as single-phase products by oxidation of Sr2 N with molecular nitrogen under high pressure.

Hierarchically porous tungsten oxide nanotubes with crystalline walls made of the metastable orthorhombic polymorph

A simple route towards highly crystalline and hierarchically porous tungsten oxide nanotubes is presented. Interestingly, due to the limited wall thickness, the metastable orthorhombic high-temperature polymorph could be stabilized for the first time at room temperature without doping. In brief, ammonium metatungstate (AMT) is grafted over core-crosslinked poly(butadiene)-block-poly(2-vinylpyridine) (PB-b-P2VP) nanorods at pH 3. Coulomb interactions between protonated PB-b-P2VP nanorods (pKa 4.5) and metatungstate anions promote hybrid formation. Subsequent calcination of the PB-b-P2VP–AMT hybrid material at 490 °C results in a non-woven structure of hierarchically porous and crystalline, orthorhombic tungsten oxide nanotubes as confirmed by electron microscopy, X-ray diffraction, and nitrogen physisorption.

Synthese und struktur von Li3RhH4, einem ternären hydrid mit planaren [RhH4]3--Baueinheiten

Zusammenfassung Die Synthese des ternaren Rhodiumhydrids Li3RhH4 gelingt durch Umsetzung von Lithiumhydrid mit Leinverteiltem Rhodium in einer hochreinen Wasserstoffatmosphare. Rontgenographische Untersuchungen an pulverformigen Proben und ein elastisches Neutronenbeugungsexperiment an der deuterierten Verbindung fuhrten zur Strukturaufklarung. Charakteristisch fur die orthorhombische Struktur (Raumgruppe: Cmcm; a=3,883(1) A b=9,022(2) A ; c=8,891(2) A ; Z=4 ) sind planare [RhH4]3--Baueinheiten. Die kurzen Abstande zwischen den Baugruppen weisen auf Wechselwirkungen zwischen den Rhodiumatomen hin.

Hydrogen dynamics in heavy alkali metal hydrides obtained through inelastic neutron scattering

Inelastic neutron scattering spectra from polycrystalline NaH, KH, RbH and CsH, measured at low temperature in the energy transfer range 3 meV<E< 500 meV, are reported. From the medium-energy regions, coinciding with the optical phonon bands, accurate hydrogen-projected densities of phonon states are extracted and compared to ab initio lattice dynamics results. The overall agreement is very good. Further lattice dynamics calculations, based on a pairwise Born–Mayer semi-empirical potential scheme, were also performed, providing only limited and qualitative agreement with the experimental data. In conclusion, incoherent inelastic neutron spectroscopy proves to be a stringent validation tool for lattice dynamics simulations of H-containing materials.

Rb3ReH10, ein neues Hydrid des siebenwertigen Rheniums - Hochdrucksynthese und Kristallstruktur

Uber eine Reaktion von Rubidiumhydrid mit Rhenium in einer Wasserstoffatmosphare bei einem Druck oberhalb von 4000 bar konnte im Temperaturbereich zwischen 700 und 870 K das ternare Hydrid Rb3ReH10 dargestellt werden. Rontgenographische Untersuchungen an einer pulverformigen Probe sowie Neutronenbeugungsexperimente an der deuterierten Verbindung fuhrten zur Strukturaufklarung. Bei Raumtemperatur existiert eine kubische Atomanordnung, die entsprechend der Schreibweise [ReD9]DRb3 eine dem Perowskit analoge Struktur besitzt. Das von den Deuteriumatomen gebildete Koordinationspolyeder der Rheniumatome kann kristallographisch uber eine statistisch unterbesetzte Belegung von zwei 24-zahligen Punktlagen beschrieben werden. In einer rhombischen Tieftemperaturmodifikation nehmen die Deuteriumliganden die geordneten Positionen eines einfach uberdachten vierseitigen Antiprismas ein. Die Verbindung zeigt diamagnetisches Verhalten. Rb3ReH10, a New Rhenium(VII) Hydride – High Pressure Synthesis and Crystal Structure The ternary hydride Rb3ReH10 can be synthesised by reacting rubidium hydride with rhenium in a hydrogen atmosphere under a pressure of above 4000 bar in a temperature range between 700 and 870 K. X-ray investigations on powder samples and elastic neutron diffraction experiments on the deuterated compound led to the crystal structure. According to the formula [ReD9]DRb3 the atomic arrangement of the room temperature modification corresponds to that of the perowskite structure type. The coordination polyhedron of the hydrogen atoms that surround each rhenium atom can be described crystallographically as a statistical occupation of two 24-fold positions with hydrogen. In the orthorhombic low-temperature modification the deuterium ligands are arranged in ordered positions. They form monocapped square antiprisms. Magnetic susceptibility measurements revealed Rb3ReD10 to be diamagnetic.

Direct Imaging of Octahedral Distortion in a Complex Molybdenum Vanadium Mixed Oxide

Complex Mo,V-based mixed oxides that crystallize in the orthorhombic M1-type structure are promising candidates for the selective oxidation of small alkanes. The oxygen sublattice of such a complex oxide has been studied by annular bright field scanning transmission electron microscopy. The recorded micrographs directly display the local distortion in the metal oxygen octahedra. From the degree of distortion we are able to draw conclusions on the distribution of oxidation states in the cation columns at different sites. The results are supported by X-ray diffraction and electron paramagnetic resonance measurements that provide integral details about the crystal structure and spin coupling, respectively.

New alkali metal osmium- and ruthenium hydrides

Abstract Previously unknown ternary metal hydrides AxOsHz and AxRuHz (A=alkali metal) were synthesized by the reaction of alkali metal hydrides with osmium or ruthenium under a hydrogen pressure up to 6000 bar. The crystal structures of the hydrides were determined using a combination of X-ray and neutron diffraction experiments with deuterated compounds on powdered samples. Na3OsH7 and Na3RuH7 crystallize at room temperature in a tetragonal structure type (space group: P42/mnm), which is characterized by isolated [OsH7]- or [RuH7] anions. The coordination polyhedron formed by the seven hydrogen (deuterium) ligands can be described as a distorted pentagonal bipyramide. Magnetic susceptibility measurements on Na3OsH7 in the temperature range between 3.5 K and room temperature revealed a weak temperature independent paramagnetism. Quantum mechanical calculations confirm these facts and show in detail that the large value of the spin–orbit coupling constant is responsible for the magnetic behaviour of these compounds with the oxidation state +4 for the transition metal atoms. With the heavier alkali metals transition metal(IV) hydrides A3−δOsH7−δ and A3−δRuH7−δ could be synthesized. They crystallize with isotypic atomic arrangements related to the cryolite structure type. Highest hydrogen pressure during the reaction leads to the osmium(VI) hydrides Cs3OsH9 and Rb3OsH9. The atomic arrangement is characterized by [OsH8] polyhedra intercalated in a cubic HA3 framework which corresponds to the ReO3 structure type. Within these polyhedra the hydrogen ligands occupy two 24-fold positions with a statistical distribution.

Silica-supported Au@hollow-SiO2 particles with outstanding catalytic activity prepared via block copolymer template approach

Catalytically active Au@hollow-SiO2 particles embedded in porous silica support (Au@hollow-SiO2@PSS) were prepared by using spherical micelles from poly(styrene)-block-poly(4-vinyl pyridine) block copolymer as a sacrificial template. Drastic increase of the shell porosity was observed after pyrolytic removal of polymeric template because the stretched poly(4-vinyl pyridine) chains interpenetrating with silica shell acted as an effective porogen. The embedding of Au@hollow-SiO2 particles in porous silica support prevented their fusion during pyrolysis. The catalytic activity of Au@hollow-SiO2@PSS was investigated using a model reaction of catalytic reduction of 4-nitrophenol and reductive degradation of Congo red azo-dye. Significantly, to the best of our knowledge, Au@hollow-SiO2@PSS catalyst shows the highest activity among analogous systems reported till now in literature. Such high activity was attributed to the presence of multiple pores within silica shell of Au@hollow-SiO2 particles and easy accessibility of reagents to the catalytically active sites of the ligand-free gold surface through the porous silica support.

Optimized thermoelectric performance of the n-type half-Heusler material TiNiSn by substitution and addition of Mn

Alloys based on the half-Heusler compound TiNiSn with the addition of Mn or with a substitution of Ti by Mn are investigated as high-temperature thermoelectric materials. In both materials an intrinsic phase separation is observed, similar to TiNiSn where Ti has been partially substituted by Hf, with increasing Mn concentration the phase separation drastically reduces the lattice thermal conductivity while the power factor is increased. The thermoelectric performance of the n-type conducting alloy can be optimized both by substitution of Ti by Mn as well as the addition of Mn.

Location and Vibrations of Hydrogen in La2C3H1.5

We report on the incorporation of hydrogen into La2C3 and on the characterisation of its position. Temperature-dependent X-ray investigations show that the hydrogenation process is reversible and the product La2C3H1.5 is amorphous. In principle, IR and Raman spectroscopies can provide some structural information, but in the present study, they are of only limited value. Inelastic neutron scattering (INS) has advantages for measuring the H-vibrations in La2C3H1.5 and these are compared with the results of molecular dynamics simulations. A structural model based on published pair-potentials predicts that hydrogen (or deuterium) occupies the “tetrahedral” holes in the lanthanum sublattice. This model also accounts for the observed vibrational spectra. Lokalisierung von Wasserstoff und seine Schwingungen in La2C3H1.5 Wir berichten uber die Einlagerung von Wasserstoff in La2C3 und die Bestimmung seiner Lagen. Temperaturabhangige rontgenographische Untersuchungen zeigen, dass der Hydrierungsprozess reversibel und das Reaktionsprodukt La2C3H1.5 amorph ist. Prinzipiell konnen IR und Raman spektroskopische Untersuchungen strukturelle Informationen liefern, aber in unserem Fall sind sie nur von geringem Wert. Unelastische Neutronenstreuexperimente (INS) dagegen haben Vorteile zur Untersuchung der Wasserstoffschwingungen in La2C3H1.5 und diese werden mit den Ergebnissen der molekular dynamischen Simulationen verglichen. Ein strukturelles Modell basierend auf den veroffentlichten „pair-potentials” sagt voraus, dass Wasserstoff (oder Deuterium) die tetraedrischen Lucken im Lanthan-Teilgitter besetzt. Dieses Modell erklart ebenfalls die beobachteten Schwingungsspektren.