Novel enantiopure bis(pyrrolo)tetrathiafulvalene donors exhibiting chiral crystal packing arrangements

Two novel enantiopure bis(pyrrolo[3,4-d])tetrathiafulvalene derivatives, substrates for preparing chiral conducting materials, show chiral crystal packing arrangements in which successive layers are rotated in accordance with an exact or approximate 43 axis. The corresponding donors containing fused dihydropyrrolegroups, and thus four more hydrogen atoms, form stacks along a crystal axis

N,N′-Bis(4-chloro-3-fluoro­benzyl­idene)ethane-1,2-diamine

The asymmetric unit of the title Schiff base compound, C16H12Cl2F2N2, contains one half of the centrosymmetric mol­ecule. Mol­ecules related by translation along the a axis form stacks with short inter­molecular C⋯C distances of 3.429 (3) Å. The crystal packing also exhibits short inter­molecular Cl⋯F contacts of 3.087 (1) Å

2-Methylxanthen-9-one

In the title compound, C14H10O2, the tricycle is not planar, being bent with a dihedral angle of 4.7 (1)° between the two benzene rings. In the crystal, π–π inter­actions between the six-membered rings of neighbouring mol­ecules [centroid–centroid distances = 3.580 (3) and 3.605 (3) Å] form stacks propagating along [101]

3-Hy­droxy-1,2-dimeth­oxyxanthone

The title compound (systematic name: 3-hy­droxy-1,2-dimeth­oxy-9H-xanthen-9-one), C15H12O5, was isolated from Polygala arillata. The tricyclic unit is essentially planar (r.m.s. deviation = 0.039 Å). In the crystal, the mol­ecules form stacks along the a axis. Inter­molecular O—H⋯O hydrogen bonds link the mol­ecules into chains parallel to [010]

Stacks of group representations

We start with a small paradigm shift about group representations, namely the observation that restriction to a subgroup can be understood as an extension-of-scalars. We deduce that, given a group $G$, the derived and the stable categories of representations of a subgroup $H$ can be constructed out of the corresponding category for $G$ by a purely triangulated-categorical construction, analogous to \'etale extension in algebraic geometry. In the case of finite groups, we then use descent methods to investigate when modular representations of the subgroup $H$ can be extended to $G$. We show that the presheaves of plain, derived and stable representations all form stacks on the category of finite $G$-sets (or the orbit category of $G$), with respect to a suitable Grothendieck topology that we call the sipp topology. When $H$ contains a Sylow subgroup of $G$, we use sipp Cech cohomology to describe the kernel and the image of the homomorphism $T(G)\to T(H)$, where $T(-)$ denotes the group of endotrivial representations.Comment: Slightly revised version of the 2012 June 21 versio

Dibutyl 2,2′-bipyridine-4,4′-dicarboxyl­ate

In the title compound, C20H24N2O4, the mol­ecule lies on a centre of symmetry and is approximately planar (r.m.s. deviation= 0.013 Å for 26 non-H atoms). The carboxyl­ate group is inclined slightly to the neighbouring pyridine ring, forming a dihedral angle of 4.37 (2)°. The mol­ecules form stacks with an inter­planar separation of 3.547 (1) Å

Photophysical characterizations of 2-(4-Biphenylyl)-5 phenyl-1,3,4- oxadiazole in restricted geometry

Langmuir and Langmuir-Blodgett (LB) films of nonamphiphilic 2-(4-Biphenylyl)-5 phenyl-1,3,4- oxadiazole (abbreviated as PBD) mixed with stearic acid (SA) as well as also with the inert polymer matrix poly(methyl methacrylate) (PMMA) have been studied. Surface pressure versus area per molecule (-A) isotherms studies suggest that PBD molecules very likely stand vertically on the air-water interface and this arrangement allows the PBD molecules to form stacks and remain sandwiched between SA/PMMA molecules. At lower surface pressure phase separation between PBD and matrix molecules occur resulting due to repulsive interaction. However at higher surface pressure PBD molecules form aggregates. The UV-Vis absorption and Steady state fluorescence spectroscopic studies of the mixed LB films of PBD reveal the nature of the aggregates. H-type aggregates predominates in the mixed LB films whereas I-type aggregates predominates in the PBD-PMMA spin coated films. The degree of deformation produced in the electronic levels are largely affected by the film thickness and the surface pressure of lifting.Comment: 15 pages, 6 figure

(3,5-Dimethyl­pyrazol-1-yl)[5-(3,5-dimethyl­pyrazol-1-ylcarbon­yl)-2-thien­yl]methanone

The title compound, C16H16N4O2S, crystallizes with two symmetry-independent half-mol­ecules in the asymmetric unit. All non-H atoms in each molecule lie in a crystallographic mirror plane. The mol­ecules form sheets in the ac plane, which then form stacks along the b axis. The sheets are connected via π–π stacking inter­actions [centroid–centroid distance between pyrazolato rings = 3.6949 (8) Å]

catena-Poly[tris(2,4,6-trimethyl­anilinium) [(tetrachloridocadmium)-μ-chlorido]]

The asymmetric unit of the title compound, {(C9H14N)3[CdCl5]}n, comprises three 2,4,6-trimethyl­aniline dications and one half of the [Cd2Cl10]6− anion. The Cd atoms are each coordinated by six Cl atoms, with octa­hedra linked by bridging, apical Cl atoms, forming linear chains running parallel to the a axis. The trimethylanilinium cations form stacks between the chains of CdCl6 octa­hedra