No abstract

2,3,7,8-Tetramethoxychalcogenanthrenes ( 5,10-chalcogena-cyclo-diveratrylenes, 'Vn2E2', E = S, Se) form isotypical 1 : 1 chargetransfer (CT) complexes with 2,3-dichloro-5,6-dicyano-174-benzoquinone (DDQ). X-ray analysis of Vn, S2 -DDQ shows the compound to have a columnar structure with segregated stacks of donors and acceptors. The donors are virtually planar in accordance with a formulation of [VnzE2] '[DDQ] -. Donor cations and acceptor anions are equidistant in their respective stacks, but in each case they inclined to the stacking axis, nevertheless guaranteeing an optimum overlap of the half-filled frontier orbitals which are of n-type character according to MNDO calculations. Dielectric ac measurements of permittivity E' and loss factor E" clearly reveal two processes, a dielectric one at low temperatures and a conductive one at high temperatures. The dielectric process can be described by the Havriliak-Negami (HN) and the Kohlrausch-Williams-Watts (KWW) model, and the conductive process by a Debye-type plot. Using these methods, the relevant parameters are evaluated. The dc conductivities of polycrystalline samples moulded at lo8 Pa show a temperature dependence in the plots of In t~ us. T -l , which is typical of semiconductors. Two slopes are found; that in the low-temperature region (< 285 K) is explained by an easy-path model (intragrain conductivity with low activation energies), whereas in the high-temperature region conduction across the grain boundaries (with higher activation energies) is becoming predominant. The activation energies for the intrinsic conductivities obtained by the ac and dc measurements are similar. Despite the columnar structure with segregated stacks, due to stoichiometric oxidation states of the components, the absolute values of conductivity are low (ca.

We have performed optical microscopy, micro-photoelectron spectroscopy, and micro-Raman scattering measurements on Y0.63Ca0.37TiO3 single crystals in order to clarify the interplay between the microstructure and the temperature dependent electronic transport mechanisms in this material. Optical microscopy observations reveal dark and bright domain patterns on the surface with length scales of the order of several to a hundred micrometers showing a pronounced temperature dependent evolution. Spatially resolved photoelectron spectroscopy measurements show the different electronic character of these domains. Using micro-Raman spectroscopy, we observe a distinct temperature dependence of the crystal structure of these domains. On the basis of these findings the different domains are assigned to insulating and metallic volume fractions, respectively. By decreasing the temperature, the volume fraction of the conducting domains increases, hence allowing the electrons to percolate through the sample at temperatures lower than ∼150 K.

X-ray analysis shows silver(I) aminomethylnitrosolate to have dimers as structural units, in which the W-shaped nitrosolate ions act as μ2-bridging ligands via the nitrogen atoms of the NO groups. The nearly planar dinuclear complexes form stacks, which are connected by additional AgO contacts leading to a kind of layer structure. These layers are held together by hydrogen bonds.Mononuclear complexes of composition [Ag(nitrosolate)L2] can be obtained from silver(I) ethylnitrosolate and bipyridyl in methanol and from silver(I) benzylnitrosolate and triphenylphosphane in diethylether/liquid ammonia. In these complexes the nitrosolate ions are supposed to act as chelating ligands, again with N,N′-coordination.

The new compound La