Anton Lerf

Redox reactions of layered transition metal disulfides in alkali halide melts

Abstract Layered ternary Sulfides, A 0.5 TiS 2 and A 0.5 .5NbS 2 (with A = Li, Na, K, Rb, Cs), were obtained by the reaction of TiS 2 and NbS 2 in alkali halide melts with H 2 S, in a flow reactor system at 800−1000 °C. On contact with water the ternary compounds give the hydrated phases, A 0.5 (H 2 O) y [TiS 2 ] and A 0.5 (H 2 O) y [NbS 2 ], with polyelectrolyte character. TaS 2 , under similar conditions, in an inert gas atmosphere yields layered tantalum sulfides A 0.3 TaS 2 . Redox reactions of transition metal complexes soluble in the halide melts are supposed to be responsible for the formation of the ternary chalcogenides.

Time differential perturbed angular correlation of γ-rays emitted from 99Mo → 99Tc in molybdenum-based catalysts: The nature of molybdate species in molybdena/alumina catalysts

The time differential observation of the perturbed angular correlation of γ-rays emitted from radioactive 99Mo → 99Tc allows one to characterize different Mo species by their nuclear quadrupole interaction. An elementary introduction to this hyperfine spectroscopy is given together with examples of its application to crystalline Mo compounds, molybdate solutions at 77 and 300 K, and molybdates adsorbed on Al2O3 in the impregnated as well as in the dried and calcined state. It is shown that at sufficiently high solution concentrations, the heptamolybdate anion is adsorbed on the Al2O3 surface. Decondensation prior to adsorption can be excluded. The adsorbed heptamolybdate species are stable during the drying and calcination process. Postimpregnation of calcined MoAl2O3 catalysts with K2CO3 leads to decondensation, the extent of which depends on K2CO3 loading.

A crystal structure investigation of the hydrated layered chalcogenides Kx(H2O)yNbS2 and Kx(H2O)yTaS2

The hydrated ternary sulphides K0.5(H2O)yNbS2 and K0.33(H2O)yTaS2 are isotypic and crystallize in hexagonal structures with the parameters a = 3.35 A, c = 17.94 A (Nb) and a = 3.336 A, c = 18.18 A (Ta); the space group is P62c. In the S-M-S sandwich layers the transition metal atoms have trigonal prismatic coordination. With respect to the arrangement of the layer units, the structures of these compounds are similar to those of the unhydrated ternary phases AxMS2 and the pyridine intercalation compound TaS2(py)0.5- Stacking disorder phenomena of the layers and high thermal mobility of the interlayer atoms prevented the location of alkali and oxygen atoms at room temperature.

Intercalation compounds in layered Host lattices: Supramolecular Chemistry in nanodimensions

Publisher Summary The term interstitial compounds should be restricted to those inorganic solids in which the additional atoms occupy empty lattice sites of the host structure with small crystal expansions and without other structural changes. These compounds are normally prepared at very high temperatures, and the atoms taken up in the solid are immobile at room temperature. Peculiar for solids forming intercalation compounds are anisotropic bonding relationships leading to stable structural elements like chains, layers, or three-dimensional frameworks. Intercalation chemistry is the soft chemistry route to such assemblies, working at the borderlines of solution chemistry, solid-state chemistry, and colloid chemistry. It is ideally suited to the fabrication of organic/inorganic multilayer assemblies. With a few exceptions (alkylammonium intercalation compounds, the hydrated metal intercalation compounds, the pyridine intercalation compounds) the experimental basis for a comparison is often very sparse: researchers in the different branches follow their own logic without looking precisely enough at the neighboring branches. The intercalation compounds of organometallic complexes in the various host lattices have been reviewed only once by Yamagishi, but this review is restricted to complexes in clay minerals and to the specialized topic of chiral recognition. There is no recent review of high-resolution NMR studies of organic species in clay minerals; in general, hyperfine techniques do not always receive the attention which they deserve.

Intercalation Compounds of Large Organic Molecular Cations in the Layered Dichalcogenide 2H-TaS2

We report on the first successful intercalation of organic cations in large crystals of 2H-TaS2 by electrochemical methods. The following species have been intercalated: Tetramethylammonium, methylviologen and methylene blue. Whereas the first species can be intercalated in chemical equilibrium like the hydrated metal ions, the intercalation of the other two more complex cations is accompanied by side reactions. The most complex system is methylene blue/TaS2 where we observe three different phases depending on the preparation conditions. The electrical resistivity as a function of temperature has been measured by a 4-point ac method on single crystals immediately after intercalation. All samples are superconductors, some of them having a transition temperature to the superconducting state Tc of 4.9 K, which is quite high for organic molecule intercalation compounds of 2H-TaS2. The anomaly of the resistivity at 77 K in the empty host lattice is suppressed in all of the intercalated samples even at the very low charge transfer of n = 0.06.

Elektrochemische Untersuchungen von BEDT-TTF / Electrochemical Investigations of BEDT-TTF

The electrochemistry of BEDT-TTF+ was investigated by means of cyclic voltammetry in solvents most frequently used for the electrocrystallization of radical cations of this donor. It can be shown that the reversibility of redox reactions is decreasing with the scan rate, with a significant influence of solvent. The results presented allow conclusions about the mechanism of electrocrystallization.

Wideline 1H NMR Study on Hydrated Layered Sulfides K0.5(H2O)y[NbS2] and Na0.5(H2O)y[NbS2]

H NMR spectra of different hydration stages show that the water molecules in hydrated layered niobium sulfides A0.5(H2O)y[NbS2] are rather mobile at room temperature. A structural scheme of water arrangement in the interlayer space is proposed with the C2-axis of the H2O molecules parallel to the basal planes of the NbS2 layer units.

METASTABLE CONFIGURATIONS DURING LITHIUM INTERCALATION INTO 2H-TAS2

Etude de la lithiation electrochimique et chimique de 2H-TaS 2 . On observe 2 types de configurations metastables