This modification of Nb2Os crystallizes in the space group Pbam with unit-cell dimensions a = 6" 175 (1), b= 29.175 (4) and c= 3.930 (1) A. The structure was determined and refined by the full-matrix leastsquares method based on 725 X-ray diffraction intensities collected on a four-circle diffractometer. The conventional R value is 0-054. The unit cell contains Nb16.aO42; Dx = 5-236 g cm-3. The 16 Nb atoms lie in a sheet parallel to (001) and are surrounded by seven or six oxygen atoms forming pentagonal bipyramidal or distorted octahedral coordination polyhedra respectively. These polyhedra are joined by edge-or corner-sharing within the (001) sheet and exclusively by corner-sharing along [001]. The remaining Nb atoms occupy those interstitial sites at random which lie between the (001) sheets of the other Nb atoms and are surrounded by nine oxygen atoms. The structure is similar to but not identical with that of fl-Ta2Os,

Anthra[2,3-b]thieno[2,3-d]thiophene (ATT), which is readily accessed from thieno[3,2-b]thiophene and 2,3-naphthalenedicarboxylic anhydride, allows for selective substitution at the terminal thiophene ring, thereby providing asymmetric monoalkyl and monoalkylthienyl thienoacenes. Alkyl-substituted ATT (CnATT, n = 6, 8, 10, 12) has characteristics of a p-type field-effect transistor (FET), with mobility on the order of 0.01 cm V s, which is the same as ATT. Conversely, alkylthienyl-substituted ATT (CnTATT, n = 6, 8, 10, 12) exhibits FET mobility of 0.15-1.9 cm V s, which is up to 2 orders of magnitude greater than that of ATT and CnATT. Moreover, CnTATT forms crystalline thin films both by spin coating and drop casting, and C8TATT in particular exhibits a mobility of up to 1.6 cm V s in the drop-cast film. X-ray diffraction patterns of CnTATT thin films indicate that the molecules become oriented edge-on at the substrate surface with a highly ordered structure in the in-plane direction. Accordingly, CnTATT serves as a solution-processable p-type organic field-effect transistor, where the additional thiophene ring contributes significantly to the highly ordered thin-film structure and the high carrier mobility.

Polycyclic aromatic compounds are attractive candidates for organic semiconductor materials whose optical and charge transport properties are significantly influenced by the molecular and packing structures. In this work, we investigated the crystal structure and physical properties of asymmetric bentshaped thienoacenes, which have a thieno[3,2-b]thiophene unit at the end of the fused aromatic ring core, and their thienyl extended-type derivatives. Among the naphthalenebased analogs, naphtho [2,3-b]thieno [2,3-d]thiophene and its thienyl derivative gave an antiparallel slip-stack structure. In contrast, among the anthracene-based analogs, anthra [2,3-b] thieno [2,3-d]thiophene produced an antiparallel slip-stack structure, while its thienyl derivative gave a layered structure with a large molecular orbital overlap. In extended conjugated systems, molecular symmetry of the long axis and dispersion forces were improved, resulting in the formation of crystal structures with large intermolecular interactions. These results suggest the importance of both the extension and molecular symmetry of a conjugated system to controlling the molecular structure.

The characteristics of the in-beam electron impact mass spectra of 13 N-carbobenzoxyoligopeptides (up to pentapeptides) composed mainly of leucine and isoleucine, and their alkyl and N-hydroxysuccinimide esters are described. In the cases of di- and tripeptide derivatives, each in-beam electron impact spectrum exhibited an abundant [M + 1]+ peak as well as amino-acyl fragments. However, in the case of pentapeptides the in-beam spectra measured under the routine conditions corresponded to the conventional electron impact spectra of the cyclopeptide derivatives formed by thermal cyclization in the mass spectrometer and few [M + 1]+ ions of the original peptides were observed. From the studies on temperature spectral change of in-beam electron impact spectra it became clear that rapid heating of the sample over the temperature range 200-300 degrees C gave abundant [M + 1]+ ions as well as fragment ions originating from the thermally intact peptide as the major peaks in the spectrum.

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