C 60 ·Se 8 ·CS 2 was prepared, for the first time, by slow concentration of a solution of C 60 and Se 8 in carbondisulfide. The crystal structure (P2 1 /c, a ϭ 1330.05(17), b ϭ 2900.6(4), c ϭ 988.09(13) pm, b ϭ 91.760(2)°; Z ϭ 4; 8910 independent reflections; R 1 ϭ 0.073; wR 2 ϭ 0.186) contains fully ordered fullerene molecules. It may be derived from the NiAs-structure-type with Se 8 -rings and CS 2 filling the octahedral voids of the distorted hex-1387 agonal close packing of fullerene molecules. The results are completed by Raman-spectroscopic and thermogravimetric investigations.
The sodium cobaltate system NaxCoO2 is a prominent representant of strongly correlated materials with promising thermoelectric response. In a combined theoretical and experimental study we show that, by doping the Co site of the compound at x=0.7 with iron, a further increase of the Seebeck coefficient is achieved. The Fe defects give rise to effective hole doping in the high-thermopower region of larger sodium content x. Originally filled hole pockets in the angular-resolved spectral function of the material shift to low energy when introducing Fe, leading to a multisheet interacting Fermi surface. Because of the higher sensitivity of correlated materials to doping, introducing adequate substitutional defects is thus a promising route to manipulate their thermopower.
The crystal structure of C 70 Á Se 8 Á CS 2 was determined from single crystal X-ray diffraction data at 100 K. Due to some peculiarities of the space group Pca2 1 and the presence of local centres of symmetry, the crystal structure refinement turned out to be problematic. Instead of stabilizing the refinement procedure by means of a very high number of restraints about direct neighbour distances and -angles, and the shape of the probability density function of the carbon atoms of the fullerene molecules, the molecular structure of the C 70 molecules was treated as a rigid body applying a local symmetry restraint in a local coordinate framework, and the TLS-formalism, using the JANA2000 program. The crystal structure may be derived from the NiAs structure type, with the fullerene molecules forming a highly distorted hexagonal closed packing. In order to enable lone-pair-p-interactions between the fullerene and the chalcogene molecules, the Se 8 -rings are shifted from the centres of the octahedral voids towards the triangular faces.
Cetyltrimethylammonium bromide (CTAB) and dodecyltrimethylammonium bromide (DTAB) form with sulphur dioxide crystalline solvates which have been characterised by Raman spectroscopy and X-ray powder diffraction (XRPD) at room temperature. In both crystal structures, the fully extended CTAB and DTAB cations are oriented along the a axes, forming infinite parallel stacks along the b axes. Neighbouring stacks form sheets with the bromide anions and the sulphur dioxide molecules acting as chelating agents. Consecutive sheets are flipped and shifted, thus building the three-dimensional crystal structure in a brick-like manner.
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