2H-Chromene-2-thione

The crystal structure of the title compound, $C_9H_6$OS, also known as 2-thiocoumarin, has been determined. The molecule is essentially planar and crystals may display second harmonic generation (SHG) effects

Variable temperature x-ray crystal structure analysis of a type I langbeinite: Rb2Cd2(SO4)(3)

The structure of a type I langbeinite, Rb2Cd2(SO4)(3), displays three different phases, cubic with a = 10.378(5) Angstrom (space group P2(1)3) at room temperature, monoclinic at 120 K with a = 10.328(3), b = 10.322(3), c = 10.325(3) Angstrom, beta = 89.975(1)degrees (space group P2(1)), and orthorhombic at 85 K with a = 10.319(2), b = 10.321(2), c = 10.320(2) Angstrom (space group P2(1)2(1)2(1)), respectively. Precise single-crystal analyses of these phases indicate that Rb2Cd2(SO4)(3) distorts initially from cubic to monoclinic upon cooling followed by a significant reorientation of the SO4 tetrahedra, resulting in an orthorhombic symmetry upon further cooling. The three structures have been established unequivocally using the same crystal. There is no indication of the formation of an intermediate triclinic phase or any lattice disorder as conjectured in several earlier reports on compounds belonging to the type I langbeinite. The bond valence sum analyses of the coordination around the Rb sites indicate asymmetry in the bond strengths which could be the driving force of the ferroelectric behavior in these materials

Propensity of formation of zipper architecture vs. Lincoln log arrangement in solvated molecular complexes of melamine with hydroxybenzoic acids

Molecular complexes of melamine with hydroxy and dihydroxybenzoic acids have been analyzed to assess the collective role of the hydroxyl (OH) and carboxyl (COOH) functionalities in the recognition process. In most cases, solvents of crystallization do play a major role in self-assembly and structure stabilization. Hydrated compounds generate linear chains of melamine molecules with acid molecules pendant resulting in a zipper architecture. However, anhydrous and solvated compounds generate tetrameric units consisting of melamine dimers together with acid molecules. These tetramers in turn interweave to form a Lincoln log arrangement in the crystal. The salt/co-crystal formation in these complexes cannot be predicted apriori on the basis of Delta pK(a) values as there exists a salt-to-co-crystal continuum

Dimorphic Forms in a Non-Centrosymmetric Environment from a Prochiral Molecule: Cooperative Interplay of Strong Hydrogen Bonds and Weak Intermolecular Interactions

4-Fluoro-N-(2-fluorophenyl) benzamide, a prochiral molecule, exhibits dimorphic behavior. This feature has been analyzed in terms of morphology, X-ray single-crystal structure analysis, differential thermal analysis, and measurement of second harmonic generation (SHG) in both forms, which crystallize in noncentric space groups. The dimorphs have different morphologies, a major form as needles and a minor form as thin plates, occurring concomitantly in the same crystallization setup. The plates crystallize in the monoclinic space group $P2_1$, while the needles are in the orthorhombic space group $Pca2_1$. Strong N-H \cdot\cdot\cdot O hydrogen bonds and weak but highly directional C-H \cdot\cdot\cdot F interactions acting cooperatively are responsible for the observed symmetry steering the molecules to pack in noncentric environments

Disorder Induced Concomitant Polymorphism in 3-Fluoro-N-(3-fluorophenyl)benzamide

The occurrence of concomitant polymorphism in 3-fluoro-N-(3-fluorophenyl) benzamide has been identified to be due to the disorder in the crystal structure. Of the two modifications, the plate form (Form I) crystallizes in the monoclinic centrosymmetric space group C2/c with Z = 4, and the needle form (Form II) crystallizes in the noncentrosymmetric space group P21 with Z = 2. An interesting positional disorder at the bridging atoms in both forms holds the molecular conformation identical, while subtle variations brought by N−H···O hydrogen bonds along with weak C−H···F and F···F interactions result in packing polymorphism

Analysis of intermolecular interactions involving halogens in substituted benzanilides

Crystal structures of halogen-substituted benzanilides have been analyzed in terms of weak interactions involving halogens. The fourc compounds namely 3-fluoro-N-(3-hydroxyphenyl)benzamide, 3-chloro-N-(3-hydroxyphenyl)benzamide, 3-fluoro-N-(4-methylphenyl)benzamide and 3-chloro-N-(4-methylphenyl)benzamide crystallize in monoclinic symmetry. The packing modes in the crystalline lattice generate motifs via N–H· · ·O and O–H· · ·O hydrogen bonds in structures 1 and 2 and via N–H· · ·O hydrogen bond, weak C–H· · ·F and Cl· · ·Cl interactions in structures 3 and 4. These structures when compared with the polymorphs of benzanilide show no orientational disorder and depict subtle conformational changes, which are directed by both strong hydrogen bonds and weak interactions involving halogens

Phase transitions in A4Li(HSO4)3(SO4)A_4Li(HSO_4)_3(SO_4); A = Rb, K: Single crystal X-ray diffraction studies

Abstract. The crystal structure of ferroelastic $Rb_4Li(HSO_4)_3(SO_4)$ has been determined at two temperatures, which indicates a structural phase transition, tetragonal $P4_3$ with $a = 7 \cdot 629(1) \AA$, $c = 29 \cdot 497(2) \AA$ at 293 K and monoclinic $P2_1$ with $a =7 \cdot 583(3) \AA$, $b = 29 \cdot 230(19) \AA$, $c = 7 \cdot 536(5) \AA$, $\beta = 90 \cdot 14(1)°$ at 90 K. The crystal structure of $K_4Li(HSO_4)_3(SO_4)_4$ has also been determined at two temperatures, tetragonal $P4_1$ with $a = 7 \cdot 405(1) \AA$, $c = 28 \cdot 712(6) \AA$ at 293 K and tetragonal $P4_1$ with $a = 7 \cdot 371(5) \AA$, $c = 28 \cdot 522(5) \AA$ at 100 K. The overall coordination features in both the structures have been analysed in terms of bond valence sum calculations

2H-Chromene-2-thione

The crystal structure of the title compound, $C_9H_6$OS, also known as 2-thiocoumarin, has been determined. The molecule is essentially planar and crystals may display second harmonic generation (SHG) effects