Reversible topotaktische Redoxreaktionen von Festkörpern durch Elektronen/Ionen-Transfer

Storylines in intercalation chemistry

Intercalation chemistry taking into account the interstratification and disorder phenomena is a valuable preparative tool for the design of artificial layered artificial nanostructures.

Stacking disorder in 2H-NbS2 and its intercalation compounds K x (H2O) y NbS2 II. Stacking disorder in K x (H2O) y NbS2

The intercalation reaction of hydrated K+ ions into the layered structure of 2H-NbS2 was studied using in situ X-ray diffraction. A structurally complex intercalation mechanism was observed showing several highly one-dimensionally disordered intercalated phases. A quantitative modelling of the disorder in K x (H2O) y NbS2 is presented allowing a complete understanding of the intercalation mechanism.

The Reaction Mechanism of a Complex Intercalation System: In Situ X-ray Diffraction Studies of the Chemical and Electrochemical Lithium Intercalation in Cr4TiSe8

The intercalation reaction between Cr(4)TiSe(8) and Li was investigated from a kinetic and an electrochemical perspective. The structural phase transition from monoclinic to trigonal symmetry was probed by in situ energy-dispersive X-ray diffraction (in situ EDXRD) for chemical intercalation with butyllithium (BuLi). A change in the kinetic mechanism was detected for the reaction at room temperature; this was interpreted in terms of a trend from phase boundary control to diffusion control. A single diffusion-controlled mechanism is obeyed at 60 degrees C. The electrochemical measurements and the corresponding in situ X-ray diffraction (in situ XRD) data revealed that the monoclinic host is intercalated up to the composition Li(x approximately 0.1)Cr(4)TiSe(8) before the characteristic phase transition starts. The monoclinic phase undergoes complex structural changes in the following two-phase regime. Owing to the co-existence of two phases, the cell potential is constant for 0.1<x<0.7 and 0.9<x<3.0. The subsequent intercalation into the trigonal phase leads to a pronounced increase in the cell volume of the trigonal phase that stops at x approximately 0.8. At this point, the complete reduction of Ti(IV) gives rise to a voltage drop of the cell potential. XANES measurements revealed that the reduction of Ti(IV) occurs prior to the reduction of Cr(III).

Ternary lanthanoid ruthenium gallides with a high gallium content: Ln(2)Ru(3)Ga(10) (Ln = Yb, Lu) with a new structure type and LnRu(2)Ga(8) (Ln = La-Nd) with CaCo(2)Al(8)-type structure

The title compounds were prepared by reaction of the elemental components at high temperatures. The compounds Yb(2)Ru(3)Ga(10) and Lu(2)Ru(3)Ga(10) crystallize with a new structure type, which has been determined from the single-crystal X-ray data of Yb(2)Ru(3)Ga(10): P4/mbm, Z = 2, a = 881.9(1) pm, c = 632.5(1) pm. In this structure the gallium atoms form two-dimensionally infinite double layers that extend perpendicular to the tetragonal axis. They contain two-thirds of the ruthenium atoms. The other ruthenium and the ytterbium atoms are situated between the gallium double layers. The structure is closely related to that of Mn(2)Hg(5). The latter compound may be written with the formula Mn(2)Mn(2)(square)Hg(10), thus indicating that its structure may be regarded as a defect-variant of the presently reported structure of Yb(2)Ru(3)Ga(10). The four gallides of the series LnRu(2)Ga(8) (Ln = La-Nd) crystallize with the orthorhombic CaCo(2)Al(8)-type structure (Pbam, Z = 4). This structure has been refined from single-crystal X-ray data of the cerium and neodymium compounds. Slight deviations from the ideal composition for one of the two ruthenium sites resulted in the formulas CeRu(1.913(4))Ga(8) and NdRu(1.858(4))Ga(8). Magnetic susceptibility measurements with a SQUID magnetometer indicate diamagnetism for LaRu(2)Ga(8), which is partially compensated by the expected Pauli paramagnetism. The cerium atoms in CeRu(2)Ga(8) show mixed or intermediate valent behavior, and PrRu(2)Ga(8) follows the Curie-Weiss law with no magnetic order down to 4 K.

The solid-state electrochemistry of metal octacyanomolybdates, octacyanotungstates, and hexacyanoferrates explained on the basis of dissolution and reprecipitation reactions, lattice structures, and crystallinities

The electrochemical behavior of solid microparticles of metal (Ag+, Cd2+, Co2+, Cr2+, Cu2+, Fe2+, Mn2+, Ni2+, Pb2+, and Zn2+) octacyanomolybdates, octacyanotungstates, and hexacyanoferrates has been studied by voltammetry, electrochemical quartz crystal microbalance, and microscopic diffuse reflectance spectroelectrochemical measurements. The solid microparticles have been immobilized on the surface of graphite electrodes prior to the electrochemical measurements. A comparative study of the cyclic oxidation and reduction of these compounds in the presence of potassium ions revealed that any interpretation of the electrochemistry requires the solubility equilibria of the reduced compounds to be taken into account, such as in the case of the silver salts [Ag3K[X]] and [Ag4[X]] (with X = FeII(CN)6(4-), MIV(CN)8(4-) (M = Mo, W)). Because [Ag4[X]] has a lower solubility than [Ag3K[X]], the electrochemistry is accompanied by a conversion of solid [Ag3K[X]] into solid [Ag4[X]]. Two distinct voltammetric signal systems are generated by these two compounds according to [Ag3K[X]] reversible [Ag3[X]] + K(+) + e- and [Ag4[X]] reversible [Ag3[X]] + Ag(+) + e-. When silver ions are present in the solution adjacent to the microparticles, the silver octacyanometalates and silver hexacyanoferrate show a chemically reversible and very stable voltammetric behavior. Despite the fact that the electrochemistry is based upon a single-electron/single-ion transfer reaction ([Ag4[X]] reversible [Ag3[X]] + Ag(+) + e-), more than one electrochemical signal is observed because of the simultaneous presence of amorphous and crystalline particles. This study shows that the interplay of solubility equilibria and electrochemical equilibria is generally observed for the other metal octacyanomolybdates, octacyanotungstates, and hexacyanoferrates as well.