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Triclinic
Terms modified by Triclinic Selected AbstractsImidazolium based ionic liquid crystals: structure, photophysical and thermal behaviour of [Cnmim]Br·xH2O (n = 12, 14; x=0, 1)CRYSTAL RESEARCH AND TECHNOLOGY, Issue 11 2008A. Getsis Abstract The long chain imidazolium halides [Cnmim]Br·xH2O (n = 10, 12; x = 0, 1) have been synthesized and their structural and thermal behaviour together with their photophysical properties characterized. X-ray structure analyses of the monohydrates ([C12mim]Br·H2O: triclinic, P1, no. 2, Z = 2, Pearson code aP112, a = 550.0(5) pm, b = 779.4(5) pm, c = 2296.1(5) pm, , = 81.89(5)°, , = 83.76(5)°, , = 78.102(5)°, 3523 unique reflections with Io > 2,(Io), R1 = 0.0263, wR2 = 0.0652, GooF = 1.037, T = 263(2) K; [C14mim]Br,H2O: triclinic, P1, no. 2, Z = 12, Pearson code aP11, a = 549.86(8) pm, 782.09(13) pm, c = 2511.3(4) pm, , = 94.86(2)°, , = 94.39(2)°, , = 101.83(2)°, 2063 unique reflections with Io > 2,(Io), R1 = 0.0429, wR2 = 0.0690, GooF = 0.770, T = 293(2) K) show for both compounds similar bilayered structures. Sheets composed of hydrophilic structure regions constituted by positively charged imidazolium head groups, bromide anions and hydrogen bonded water alternate with hydrophobic areas formed by interdigitated long alkyl chains belonging to imidazolium cations with different orientation. Combined differential scanning calorimetry and polarizing optical microscopy shows that the monohydrates as well as the anhydrous imidazolium salts are thermotropic liquid crystals which adopt smectic mesophases. The mesophase region is larger in case of the monohydrates when compared to the anhydrous compounds indicating that water obviously stabilizes the mesophase. All compounds show an intense whitish photoluminescence with short lived (1,,1,*) and long lived (1,,3,*) transitions. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis, crystal structure and vibrational characterization of bis-,-peroxo-hexacarbonatodicerate(IV) complexes of rubidium and cesiumCRYSTAL RESEARCH AND TECHNOLOGY, Issue 11 2008N.-P. Pook Abstract The new compounds Rb8[Ce(O2)(CO3)3]2 · 12 H2O (1) and Cs8[Ce(O2)(CO3)3]2 · 10 H2O (2) were obtained from the reaction of hydrogen peroxide and Ce(III) in saturated alkali carbonate solutions. The crystal structures and the unit cell parameters of (1) triclinic, P-1 with a = 8.973(2) Å, b = 10.815(2) Å, c = 11.130(3) Å, , = 66.992(2)°, , = 68.337(2)°, , = 74.639(2)°, VEZ = 914.7(4) Å3, Z = 2, and (2) orthorhombic, Pbca, a = 19.3840(16) Å, b = 18.528(2) Å, c = 10.487(3) Å, VEZ = 3766.4(13) Å3, Z = 8, were determined. Both compounds contain the bis-µ-peroxo-hexacarbonatodicerate(IV)-ion, [(CO3)3Ce(O2)2Ce(CO3)3]8- . IR and Raman spectra were measured and discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis and crystal structure determination of 6,7-dihydro-2-methoxy-4-(substituted)-5H -benzo[6,7]cyclohepta[1,2- b ]pyridine-3-carbonitrileCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2007A. M. Moustafa Abstract The compounds 6,7-dihydro-2-methoxy-4-(4-methylphenyl)-5H -benzo[6.7]cyclohepta[1,2 -b ]pyridine-3-carbonitrile (compound IIIa) and 4-(4-chlorophenyl)-6,7-dihydro-2-methoxy-5H -benzo[6,7]cyclohepta[1,2- b ]pyridine-3-carbonitrile (compound IIIb) were synthesized and their structures have been determined from three dimensional X-ray data using direct method and refined by full matrix least squares with anisotropic thermal parameters for non-hydrogen atoms to conventional R(gt) of 0.036 and 0.038 for the two compounds respectively. For compound (IIIa) the crystals are monoclinic, space group Cc, with a=11.2909 (5) Å, b=17.7755(8) Å, c=9.1437(4) Å and ,=95.428(3)°, while the crystals of the second compound (IIIb) are triclinic, space group P1, with a=8.7465(3)Å, b=10.3958(3)Å, c=10.9011(4)Å, ,= 108.3870(10)°, ,=101.3741(12)°, ,=97.9594(12)°. The molecular structure of the two compounds have nearly the same configuration, where the cyclohepta ring takes the boat shape and the methoxy and the carbonitrile groups are attached at the same position C2 and C8. The difference occurs only at the position C4, where the substituent is methylphenyl for compound (IIIa) and chlorophenyl for the other. The bond lengths, valency angles and the hydrogen bonding were calculated and fully discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crystal structure of a tetrazole derivativeCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2006H. S. Yathirajan Abstract 5-(4'-Methyl-1,1'-biphenyl-2-yl)-1H-tetrazole(MBT), C28H24N8, CCDC: 223082, F.W.=472.55, triclinic, P1, a=4.99(1)Å, b=14.25(4)Å, c=16.63(5)Å, , = 90.27(5)°, , = 91.19(5)°, , = 90.64(5)°, V = 1182(6)Å3, Z = 4, Dcal = 1.327 Mgm -3, , = 0.084mm -1, F000 = 496, , (MoK,) = 0.71073Å, final R1 and wR2 are 0.0924 and 0.2309, respectively. There are two crystallographically independent molecules in the asymmetric unit. The dihedral angles between the two phenyl rings of the biphenyl ring system are 44.2(2)° and 44.3(2)° for the two molecules respectively. The molecules are stabilized by N-H,N and C-H,N types of intermolecular hydrogen bonds in the unit cell in addition to van der Waals forces. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim [source] Preparation and characterization of powders and crystals of Vn-xTixO2n-1 Magneli oxidesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10-11 2005D. Calestani Abstract Vn-xTixO2n-1 Magnéli phases have been synthesized under vacuum in powder form (n = 4, 0 , x , 0.4) and crystals (n = 4 and 5, x = 0.5 and 1.4, respectively), grown by chemical vapour transport in closed ampoules. TeCl4 and NH4Cl were used as transporting agents. Needle-shaped crystals as long as 200-300 micrometers or 2-3 mm were obtained when in presence of NH4Cl or TeCl4, respectively. The powder and crystal structures were examined by X-ray diffraction and the transport and magnetic characteristics were measured.. The powders resulted to be single-phase and the relevant composition was assumed to be equal to the nominal one. The overall stoichiometry of compounds, n, was determined from single crystal X-ray diffraction data. The Ti content, x, was deduced from the elementary cell volume, by applying the Végard law. Crystals were mainly untwinned and of good quality. The elementary cell of both, powders and crystals, was triclinic (P-1) and did not change with doping. DC electrical resistivity of the crystals was measured in a four-points (van der Pauw) configuration. DC magnetic susceptibility of the powders was measured in a SQUID magnetometer. The Ti doping was found to progressively smooth and finally to suppress the magnetic transitions occurring in the V4O7. The metal-insulator transitions observed in V4O7 and V5O9, at around 235 and 125 K respectively, were not observed in the doped crystals, thus indicating some significant change of the electronic structure of the V oxides. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis, spectroscopic studies and ab-initio structure determination from X-ray powder diffraction of bis-(N-3-acetophenylsalicylaldiminato)copper(II)CRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2005S. Banerjee Abstract The synthesis, spectroscopic studies and crystal structure determination from X-ray powder diffraction have been carried out for bis-(N-3-acetophenylsalicylaldiminato)copper(II). The structure is triclinic, space group P1 with unit cell dimensions a = 11.817(1) Å, b = 12.087(1) Å, c = 9.210(1) Å, , = 102.62(1)°, , = 111.16(1)°, , = 86.15(1)°, V = 1197.0(2)Å3, Z = 2. The structure has been solved by Monte Carlo simulated annealing approach and refined by GSAS package. The final Rp value was 8.68%. The coordination geometry around the copper atom in the complex is intermediate between square-planar and tetrahedral with two salicylaldimine ligands in trans arrangement. Intermolecular C,H,O hydrogen bonds between molecules related by translation generate infinite chains along [010] direction. The molecular chains are linked via additional C,H,O hydrogen bonds to form a three-dimensional supramolecular network. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis and Characterization of Semiconductive Dichloridobis(thianthrene)gold(1+) Tetrachloridoaurate(1,)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2009Rachmat Triandi Tjahjanto Abstract A new (thianthrene)gold(III) complex has been synthesized in liquid SO2 as the solvent from thianthrene (TA) andAuCl3. [AuCl2(TA)2][AuCl4] [triclinic, P, a = 9.9832(2) Å, b = 10.3404(2) Å, c = 15.0798(4) Å, , = 75.038(1)°, , = 81.610(1)°, , = 68.409(1)°, V = 1396.15(5) Å3, Z = 2] has a salt-like structure consisting of [AuCl2(TA)2]+ and [AuCl4], ions, both with square-planar coordinated gold atoms of oxidation state +3. In the cation, two bent TA molecules are coordinated to Au each through one sulfur atom. The title compound is thermally stable up to 425 K and is semiconducting with a conductivity reaching 25 mSm,1 at 380 K and a low activation energy of 0.43 eV. A model for the charge transport along the stacked cationic complexes is discussed. When dissolved in chloroform [AuCl2(TA)2][AuCl4] is converted into the already known uncharged, mononuclear complex [AuCl3(TA)], which shows that a polymerization isomerism exists between the two forms.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Surface waves in a general anisotropic poroelastic solid half-spaceGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2004M. D. Sharma SUMMARY A method is introduced for studying surface waves in a general anisotropic poroelastic medium. The method is analogous to the one used for isotropic media and derives a complex secular equation to represent the propagation of surface waves at the stress-free plane surface of a non-dissipative porous medium. The point of importance is that the derived equation is, analytically, separable into real and imaginary parts and hence can be solved by iterative numerical methods. A root of this secular equation represents the existence of surface waves and calculates the apparent phase velocity along a given direction on the surface. Numerical work is carried out for the model of a crustal rock. The propagation of surface waves is studied numerically for the top three anisotropies (i.e. triclinic, monoclinic, orthorhombic). [source] Seismic characterization of vertical fractures described as general linear-slip interfacesGEOPHYSICAL PROSPECTING, Issue 2 2003Vladimir Grechka ABSTRACT Fluid flow in many hydrocarbon reservoirs is controlled by aligned fractures which make the medium anisotropic on the scale of seismic wavelength. Applying the linear-slip theory, we investigate seismic signatures of the effective medium produced by a single set of ,general' vertical fractures embedded in a purely isotropic host rock. The generality of our fracture model means the allowance for coupling between the normal (to the fracture plane) stress and the tangential jump in displacement (and vice versa). Despite its low (triclinic) symmetry, the medium is described by just nine independent effective parameters and possesses several distinct features which help to identify the physical model and estimate the fracture compliances and background velocities. For example, the polarization vector of the vertically propagating fast shear wave S1 and the semi-major axis of the S1 -wave normal-moveout (NMO) ellipse from a horizontal reflector always point in the direction of the fracture strike. Moreover, for the S1 -wave both the vertical velocity and the NMO velocity along the fractures are equal to the shear-wave velocity in the host rock. Analysis of seismic signatures in the limit of small fracture weaknesses allows us to select the input data needed for unambiguous fracture characterization. The fracture and background parameters can be estimated using the NMO ellipses from horizontal reflectors and vertical velocities of P-waves and two split S-waves, combined with a portion of the P-wave slowness surface reconstructed from multi-azimuth walkaway vertical seismic profiling (VSP) data. The stability of the parameter-estimation procedure is verified by performing non-linear inversion based on the exact equations. [source] A Novel Narrow Band Red-Emitting Phosphor for White Light Emitting DiodesINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 4 2009Sivakumar Vaidyanathan Research on down conversion phosphor materials is the key for the development of solid-state lighting (SSL). Especially finding alternative red phosphor for white light emitting diodes (LEDs) based on blue or near ultraviolet (NUV) LEDs is important research task. In this view, we have synthesized a series of Eu3+ -substituted La2W2,xMoxO9 (x=0,2, in step of 0.3) red phosphor and characterized by X-ray diffraction (XRD) and photoluminescence. XRD results reveal a phase transition from triclinic to cubic structure for x>0.2. All the compositions show broad charge transfer (CT) band due to CT from oxygen to tungsten/molybdenum and red emission due to Eu3+ ions. Select compositions show high red emission intensity compared with the commercial red phosphor under NUV/blue ray excitation. Hence, this candidate can be a possible red phosphor for white LEDs. [source] Conformational polymorphism in aripiprazole: Preparation, stability and structure of five modificationsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2009Doris E. Braun Abstract Five phase-pure modifications of the antipsychotic drug aripiprazole were prepared and characterized by thermal analysis, vibrational spectroscopy and X-ray diffractometry. All modifications can be produced from solvents, form I additionally by heating of form X° to ,120°C (solid,solid transformation) and form III by crystallization from the melt. Thermodynamic relationships between the polymorphs were evaluated on the basis of thermochemical data and visualized in a semi-schematic energy/temperature diagram. At least six of the ten polymorphic pairs are enantiotropically and two monotropically related. Form X° is the thermodynamically stable modification at 20°C, form II is stable in a window from about 62,77°C, and form I above 80°C (high-temperature form). Forms III and IV are triclinic (), I and X° are monoclinic (P21) and form II orthorhombic (Pna21). Each polymorph exhibits a distinct molecular conformation, and there are two fundamental N,HO hydrogen bond synthons (catemers and dimers). Hirshfeld surface analysis was employed to display differences in intermolecular short contacts. A high kinetic stability was observed for three metastable polymorphs which can be categorized as suitable candidates for the development of solid dosage forms. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:2010,2026, 2009 [source] Polymorphism and pseudopolymorphism of salicaine and salicaine hydrochloride crystal polymorphism of local anaesthetic drugs, part VJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2006A.C. Schmidt Abstract The local anaesthetic drug salicaine hydrochloride (hydroxytetracaine hydrochloride, 4-butylamino-2-hydroxybenzoic acid 2-dimethylaminoethyl ester hydrochloride, SLCHC) and the free-base salicaine (SLC) were characterized by thermal analysis, vibrational and solid-state NMR-spectroscopy, X-ray powder diffraction, X-ray single crystal structure analysis, and water vapor sorption analysis. Additionally, the crystal structures of the anhydrate mod. II° (monoclinic, space group P21/n), the hydrated mod. I (triclinic, space group ), and of the free base (SLC) in the form of the hemihydrate (triclinic, space group ) are discussed. Mod. II° of the polymorphic SLCHC is the thermodynamically stable form at room temperature and is present in commercial products mostly contaminated with a hydrated form that is isomorphic with mod. I. Mod. II° crystallizes from most organic solvents and from the melt below 110°C. Mod. I crystallizes from the melt at temperatures above 110°C, and additionally appears on dehydration of the hydrated mod. I. A third polymorph monotropically related to mod. II° was found by freeze-drying. The free-base SLC was found to crystallize from ethanol/water as a triclinic hemihydrate. © 2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 95:1097,1113, 2006 [source] Three-dimensional ordering in self-organized (In,Ga)As quantum dot multilayer structuresPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2009V. Kladko Abstract Molecular beam epitaxy (MBE) grown In0.5Ga0.5As/GaAs multilayer structures with quantum dots chains (QDs), obtained under different growth conditions, were investigated by high-resolution X-ray diffractometry (HRXRD) and AFM. It was determined that self-organized epitaxial growth of In0.5Ga0.5As/GaAs can lead to the formation of three-dimensional quantum-dot crystals with triclinic (distorted cubic) unit cell. The mechanisms of QDs ordering in dependence on As flux are analyzed. [source] Phase transitions and transport phenomena in Li0.25Cu1.75Se superionic compoundPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2004M. Kh. Abstract Phase transformation points in Li0.25Cu1.75Se mixed electronic,ionic conductor have been determined by calorimetric, conductometric and thermoelectric measurements. The phase transformation (PT) from triclinic to monoclinic occurs at 403,413 K. At 503,515 K the monoclinic phase is followed by a rhombohedral modification. Both of these PTs are accompanied by drops on the calorimetric curve. At about 653 K observed anomalies in the temperature dependencies of the ionic conductivity, of the chemical diffusion coefficient and the jump of the ionic Seebeck coefficient have been induced by the PT to hexagonal phase. Neutron diffraction studies reveal the cubic structure of Li0.25Cu1.75Se compound (with space group Fm3m) at 773 K. The corresponding PT causes anomalies in the electrical and diffusion properties at 703,713 K. Cu ions are statistically distributed over tetrahedral and trigonal voids in an Fm3m cage; lithium ions randomly occupy 32(f) positions. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Homogeneous sphere packings with triclinic symmetryACTA CRYSTALLOGRAPHICA SECTION A, Issue 6 2002W. Fischer All homogeneous sphere packings with triclinic symmetry have been derived by studying the characteristic Wyckoff positions P,1a and P,2i of the two triclinic lattice complexes. These sphere packings belong to 30 different types. Only one type exists that has exclusively triclinic sphere packings and no higher-symmetry ones. The inherent symmetry of part of the sphere packings is triclinic for 18 types. Sphere packings of all but six of the 30 types may be realized as stackings of parallel planar nets. [source] Orientational ordering, tilting and lone-pair activity in the perovskite methylammonium tin bromide, CH3NH3SnBr3ACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2010Ian Swainson Synchrotron powder diffraction data from methylammonium tin bromide, CH3NH3SnBr3, taken as a function of temperature, reveal the existence of a phase between 230 and 188,K crystallizing in Pmc21, a = 5.8941,(2), b = 8.3862,(2), c = 8.2406,(2),Å. Strong ferroelectric distortions of the octahedra, associated with stereochemical activity of the Sn 5s2 lone pair, are evident. A group analysis and decomposition of the distortion modes of the inorganic framework with respect to the cubic parent is given. The primary order parameters driving this upper transition appear to be an in-phase tilt (rotation) of the octahedra coupled to a ferroelectric mode. The precise nature of the lower-temperature phase remains uncertain, although it appears likely to be triclinic. Density-functional theory calculations on such a triclinic cell suggest that directional bonding of the amine group to the halide cage is coupled to the stereochemical activity of the Sn lone pair via the Br atoms, i.e. that the bonding from the organic component may have a strong effect on the inorganic sublattice (principally via switching the direction of the lone pair with little to no energy cost). [source] An unexpected co-crystal with a variable degree of order: 1:1 rac -1,2-cyclohexanediol/triphenylphosphine oxideACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2007Maxime A. Siegler A 1:1 co-crystal of rac - trans -1,2-C6H10(OH)2 and (C6H5)3PO has been found that is unusual because there are no strong interactions between the two kinds of molecules, which are segregated into layers. Furthermore, neither pure rac -1,2-cyclohexanediol (CHD) nor pure triphenylphosphine oxide (TPPO) has any obvious packing problem that would make the formation of inclusion complexes likely. The TPPO layers are very much like those found in two of the four known polymorphs of pure TPPO. The hydrogen-bonded ribbons of CHD are similar to those found in other vic -diol crystals. The co-crystals are triclinic (space group P), but the deviations from monoclinic symmetry (space group C2/c) are small. The magnitudes of those deviations depend on the solvent from which the crystal is grown; the deviations are largest for crystals grown from acetone, smallest for crystals grown from toluene, and intermediate for crystals grown from ethanol. The deviations arise from incomplete enantiomeric disorder of the R,R and S,S diols; this disorder is not required by symmetry in either space group, but occupancy factors are nearly 0.50 when the structure is refined as monoclinic. When the structure is refined as triclinic the deviations of the occupancy factors from 0.50 mirror the deviations from monoclinic symmetry because information about the partial R,R/S,S ordering is transmitted from one diol layer to the next through the very pseudosymmetric TPPO layer. Analyses suggest individual CHD layers are at least mostly ordered. The degree of order seems to be established at the time the crystal is grown and is unlikely to change with heating or cooling. Thermal data suggest the existence of the co-crystal is a consequence of kinetic rather than thermodynamic factors. [source] Polymorphism of 4-bromobenzophenoneACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2007Mikhail A. Strzhemechny A combination of single-crystal and powder X-ray diffractometry was used to study the structure of two polymorphs of 4-bromobenzophenone over the temperature range from 100 to 300,K. One of the polymorphs of the title compound was known previously and its structure has been determined at room temperature [Ebbinghaus et al. (1997). Z. Kristallogr.212, 339,340]. Two crystal growth methods were employed, one of which (a modification of the Bridgman,Stockbarger technique) resulted in single crystals of a previously unknown structure. The basic physical properties of the stable polymorph are: growth method, from 2-propanol solutions or gradient sublimation; space group, monoclinic P21/c; melting point, Tm = 355.2,K; X-ray density (at 100,K), Dx = 1.646,g,cm,3. The same properties of the metastable polymorph (triclinic ) are: growth method, modified Bridgman,Stockbarger method; X-ray density (at 100,K), Dx = 1.645,g,cm,3; Tm = 354,K. Thermograms suggest that the melting of the metastable form is accompanied by at least a partial crystallization presumably into the monoclinic form; the transformation is therefore monotropic. Analysis of short distances in both polymorphs shows that numerous weak hydrogen bonds of the C,H,, type ensure additional stabilization within the respective planes normal to the longest dimension of the molecules. The strong temperature dependence of the lattice constants and of the weak bond distances in the monoclinic form suggest that the weak bond interactions might be responsible for both the large thermal expansion within plane bc and the considerable thermal expansion anisotropy. [source] Structural characterization of p -benzosemiquinone radical in a solid state: the radical stabilization by a low-barrier hydrogen bondACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2006imir Mol Semiquinone (p -benzosemiquinone), a transient organic radical, was detected in the solid state by EPR spectroscopy revealing four symmetrically equivalent protons. A variable-temperature X-ray diffraction analysis (293 and 90,K) and EPR data support a dynamical disorder of the proton. A low-barrier O,H···O hydrogen bond stabilizes the radical. The C,O bond length is 1.297,(4),Å, corresponding to a bond order of ca 1.5. The geometry of the radical implies an electron delocalization throughout the benzenoid ring. Two polymorphs of semiquinone, monoclinic and triclinic, were observed and their structures determined. Their crystal packings were compared with those of quinhydrone polymorphs. [source] Order,disorder twinning model and stacking faults in ,-NTOACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2006Dieter Schwarzenbach Crystals of the recently published [Bolotina, Kirschbaum & Pinkerton (2005). Acta Cryst. B61, 577,584] triclinic (P) structure of 5-nitro-2,4-dihydro-1,2,4-triazol-3-one (,-NTO) occur as fourfold twins. There are Z, = 4 independent molecules per asymmetric unit. We show that the structure contains layers with 2-periodic layer-group symmetry p21/b 1 (1). This symmetry is lost through the stacking of the layers, which is a possible explanation for Z, = 4. A layer can assume four different but equivalent positions with respect to its nearest neighbor. Twinning arises through stacking faults and is an instructive example of the application of order,disorder theory using local symmetry operations. The near-neighbor relations between molecules remain unchanged through all twin boundaries. The four structures with maximum degree of order, one of which is the observed one, and the family reflections common to all domains are identified. Rods of weak diffuse scattering confirm the stacking model. [source] Nine N -aryl-2-chloronicotinamides: supramolecular structures in one, two and three dimensionsACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2006Silvia Cuffini Structures are reported here for eight further substituted N -aryl-2-chloronicotinamides, 2-ClC5H3NCONHC6H4X -4,. When X = H, compound (I) (C12H9ClN2O), the molecules are linked into sheets by N,H,N, C,H,,(pyridyl) and C,H,,(arene) hydrogen bonds. For X = CH3, compound (II) (C13H11ClN2O, triclinic with Z, = 2), the molecules are linked into sheets by N,H,O, C,H,O and C,H,,(arene) hydrogen bonds. Compound (III), where X = F, crystallizes as a monohydrate (C12H8ClFN2O·H2O) and sheets are formed by N,H,O, O,H,O and O,H,N hydrogen bonds and aromatic ,,, stacking interactions. Crystals of compound (IV), where X = Cl (C12H8Cl2N2O, monoclinic P21 with Z, = 4) exhibit inversion twinning: the molecules are linked by N,H,O hydrogen bonds into four independent chains, linked in pairs by C,H,,(arene) hydrogen bonds. When X = Br, compound (V) (C12H8BrClN2O), the molecules are linked into sheets by N,H,O and C,H,N hydrogen bonds, while in compound (VI), where X = I (C12H8ClIN2O), the molecules are linked into a three-dimensional framework by N,H,O and C,H,,(arene) hydrogen bonds and an iodo,N(pyridyl) interaction. For X = CH3O, compound (VII) (C13H11ClN2O2), the molecules are linked into chains by a single N,H,O hydrogen bond. Compound (VIII) (C13H8ClN3O, triclinic with Z, = 2), where X = CN, forms a complex three-dimensional framework by N,H,N, C,H,N and C,H,O hydrogen bonds and two independent aromatic ,,, stacking interactions. [source] Chiral versus racemic building blocks in supramolecular chemistry: malate salts of organic diaminesACTA CRYSTALLOGRAPHICA SECTION B, Issue 3-2 2002Dorcas M. M. Farrell (S)-Malic acid forms a salt with N,N,-dimethylpiperazine, [MeN(CH2CH2)2NMe]H22+·2C4H5O5, (1) (triclinic, P1, Z, = 1), in which the cations link pairs of hydrogen-bonded anion chains to form a molecular ladder. With 4,4,-bipyridyl, (S)-malic acid forms a 1:1 adduct which crystallizes from methanol to yield two polymorphs, (2) (triclinic, P1, Z, = 1) and (3) (monoclinic, C2, Z, = 1), while racemic malic acid with 4,4,-bipyridyl also forms a 1:1 adduct, (4) (monoclinic, P21/c, Z, = 1). In each of (2), (3) and (4) the components are linked by O,H,N and N,H,O into chains of alternating bipyridyl and malate units, which are linked into sheets by O,H,O hydrogen bonds. In each of the 1:1 adducts (5) and (6), formed by, respectively, (S)-malic acid and racemic malic acid with 1,2-bis(4,-pyridyl)ethene, the diamine is disordered over two sets of sites, related by a 180° rotation about the N,N vector. In (5), (C12H10N2)H+·C4H5O5, (triclinic, P1, Z, = 1), the components are again linked by a combination of N,H,O and O,H,O hydrogen bonds into sheets, while in (6) (triclinic, P, Z, = 0.5) there is only partial transfer of the H atom from O to N and the malate component is disordered across a centre of inversion. With 1,4-diazabicyclo[2.2.2]octane, racemic malic acid forms a 1:2 salt, [(C6H12N2)H2]2+·2C4H5O5, (7) (monoclinic, P21/c, Z, = 2), while (S)-malic acid forms a 1:1 adduct, (8) (monoclinic, P21, Z, = 3). There are thus six independent molecular components in each. In (7) the ions are linked by an extensive series of N,H,O and O,H,O hydrogen bonds into a three-dimensional framework, but in (8) there is extensive disorder involving all six components, and no refinement proved to be feasible. [source] Luminescence properties of the structure built from 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H -pyrrol-2-olate and caesium(I)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2010Viktor A. Tafeenko The structure of caesium(I) 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H -pyrrol-2-olate (CsA), Cs+·C8HN4O2,, is related to its luminescence properties. The structure of CsA (triclinic, P) is not isomorphous with previously reported structures (monoclinic, P21/c) of the KA and RbA salts. Nevertheless, the coordination numbers of the metals are equal for all salts (nine). Each anion in the CsA salt is connected by pairs of inversion-related N,H...O hydrogen bonds to another anion, forming a centrosymmetric dimer. The dimers are linked into infinite ribbons, stacked by means of ,,, interactions, thus building up an anionic wall. Time-dependent density functional theory calculations show that the formation of the dimer shifts the wavelength of the luminescence maximum to the blue region. Shortening the distance between stacked anions in the row [from 3.431,(5),Å for RbA to 3.388,(2),Å for KA to 3.244,(10),Å for CsA] correlates with a redshift of the luminescence maximum from 574 and 580,nm to 596,nm, respectively. [source] Bis[2-(2-hydroxyethyl)pyridinium] ,-decavanadato-bis[pentaaquamanganate(II)] tetrahydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009Lenka Kli, tincová The structure of the title compound, (C7H10NO)2[Mn2V10O28(H2O)10]·4H2O or (C5H4NHCH2CH2OH)2[{Mn(H2O)5}2V10O28]·4H2O, at 293,(2),K has triclinic (P) symmetry. The asymmetric unit consists of one half of a decavanadate anion of Ci symmetry, one [Mn(H2O)5]2+ group, one 2-(2-hydroxyethyl)pyridinium cation and two solvent water molecules. The decavanadate ion bridges between two [Mn(H2O)5]2+ groups, thus forming a dodecanuclear complex unit. Complex units are connected via a hydrogen-bonding network, forming supramolecular layers lying in the (001) plane. Cations and solvent water molecules are located between these layers. [source] A new polymorph of triphenylmethylamine: the effect of hydrogen bondingACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009Victor N. Khrustalev Crystallization of the hexane reaction mixture after treatment of LiGe(OCH2CH2NMe2)3 with Ph3CN3 gives rise to a new triclinic (space group P) polymorph of triphenylmethylamine, C19H17N, (I), containing dimers formed by N,H...N hydrogen bonds, whereas the structure of the known orthorhombic (space group P212121) polymorph of this compound, (II), consists of isolated molecules. While the dimers in (I) lie across crystallographic inversion centres, the molecules are not truly related by them. The centrosymmetric structure is due to the statistical disordering of the amino H atoms participating in the N,H...N hydrogen-bonding interactions, and thus the inversion centre is superpositional. The conformations and geometric parameters of the molecules in (I) and (II) are very similar. It was found that the polarity of the solvent does not affect the capability of triphenylmethylamine to crystallize in the different polymorphic modifications. The orthorhombic polymorph, (II), is more thermodynamically stable under normal conditions than the triclinic polymorph, (I). The experimental data indicate the absence of a phase transition in the temperature interval 120,293,K. The densities of (I) (1.235,Mg,m,3) and (II) (1.231,Mg,m,3) at 120,K are practically equal. It would seem that either the kinetic factors or the effects of the other products of the reaction facilitating the hydrogen-bonded dimerization of triphenylmethylamine molecules are the determining factor for the isolation of the triclinic polymorph (I) of triphenylmethylamine. [source] A commonly used spin label: S -(2,2,5,5-tetramethyl-1-oxyl-,3 -pyrrolin-3-ylmethyl) methanethiosulfonateACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2008Vitali Zielke The title compound, C10H18NO3S2, which finds application as a spin label, has triclinic (P) symmetry at 100,(2),K with two independent molecules in the asymmetric unit. Both molecules are very similar with respect to bond lengths and angles, but molecule 2 shows disordering of its side chain. The pyrroline rings differ slightly with respect to the position of the NO group, which in both cases are sterically shielded by the surrounding methyl groups. The crystal structure of the title compound represents the first example of a 2,2,5,5-tetramethyl-1-oxyl-,3 -pyrroline derivative with a side chain at the double bond which is linked to it through an sp3 -hybridized C atom. In the solid state, the side chain adopts a conformation with the methyl group above/below the pyrroline ring and a H atom directed towards a C atom of the double bond. The disordered side chain of molecule 2 represents a second conformation with low potential energy. Both molecules exhibit planar chirality, but in the solid state both pairs of stereoisomers are present. These four stereoisomers are stacked one behind the other in four different columns, denoted A, A,, B and B,, the angle between the vectors of the N,O bonds in columns A and B being 80.38,(8)°. [source] Synthetic aenigmatite analog Na2(Mn5.26Na0.74)Ge6O20: structure and crystal chemical considerationsACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2008Günther J. Redhammer Disodium hexamanganese(II,III) germanate is the first aenigmatite-type compound with significant amounts of manganese. Na2(Mn5.26Na0.74)Ge6O20 is triclinic and contains two different Na positions, six Ge positions and 20 O positions (all with site symmetry 1 on general position 2i of space group P). Five out of the seven M positions are also on general position 2i, while the remaining two have site symmetry (Wyckoff positions 1f and 1c). The structure can be described in terms of two different layers, A and B, stacked along the [011] direction. Layer A contains pyroxene-like chains and isolated octahedra, while layer B is built up by slabs of edge-sharing octahedra connected to one another by bands of Na polyhedra. The GeO4 tetrahedra show slight polyhedral distortion and are among the most regular found so far in germanate compounds. The M sites of layer A are occupied by highly charged (trivalent) cations, while in layer B a central pyroxene-like zigzag chain can be identified, which contains divalent (or low-charged) cations. This applies to the aenigmatite-type compounds in general and to the title compound in particular. [source] Two polymorphs of aqua[N,N,-ethylenebis(salicylideneaminato- N,O)]oxovanadium(V) nitrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2001Alan Hazell The title compound, aqua[bis(salicylidene)ethylenediaminato- O,N,N,,O,]oxovanadium(V) nitrate, [VO(C16H14N2O2)(H2O)]NO3, crystallizes as two polymorphs in the triclinic and monoclinic crystal systems. In both, the V atom has a distorted octahedral coordination geometry with a long V,Owater bond trans to V=O. The coordinated water molecules are hydrogen bonded to the nitrate ions so that pairs of cations are linked to give neutral centrosymmetric dimers. The V=O and V,Owater distances are 1.598,(2) and 2.257,(2),Å, respectively, in the triclinic form, and 1.588,(3) and 2.230,(3),Å, respectively, in the monoclinic form. In the triclinic form, the dimers pack so that the salen [bis(salicylidene)ethylenediaminate] ligands are parallel to each other, whereas in the monoclinic form, which is the denser, there is a herring-bone arrangement. [source] Cadmium copper tetrachloride tetrahydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2000Ulrich Kortz The double salt [CuCl2(H2O)2{CdCl2}]·2H2O crystallizes in the triclinic rather than the monoclinic system as reported previously. The structure consists of sheets in the ac plane with slightly distorted octahedral CdCl6 [Cd,Cl 2.5813,(8),2.6943,(8),Å] connected by Cd,Cl,Cd bridges in the Cd equatorial plane along a, and by Cd,Cl,Cu bridges to layers of square-planar CuCl2(H2O)2 along c. There are long axial Cu,Cl interactions of 2.8623,(7),Å and additional water of hydration is hydrogen bonded to coordinated water and chloride ligands. The additional water connects the ac sheets into a three-dimensional network. Both Cd and Cu occupy different sites. The Cu,Cu and Cd,Cd distances are 3.8274,(6),Å. [source] Analysis of multiple crystal forms of Bacillus subtilis BacB suggests a role for a metal ion as a nucleant for crystallizationACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2010M. Rajavel Bacillus subtilis BacB is an oxidase that is involved in the production of the antibiotic bacilysin. This protein contains two double-stranded ,-helix (cupin) domains fused in a compact arrangement. BacB crystallizes in three crystal forms under similar crystallization conditions. An interesting observation was that a slight perturbation of the crystallization droplet resulted in the nucleation of a different crystal form. An X-ray absorption scan of BacB suggested the presence of cobalt and iron in the crystal. Here, a comparative analysis of the different crystal forms of BacB is presented in an effort to identify the basis for the different lattices. It is noted that metal ions mediating interactions across the asymmetric unit dominate the different packing arrangements. Furthermore, a normalized B -factor analysis of all the crystal structures suggests that the solvent-exposed metal ions decrease the flexibility of a loop segment, perhaps influencing the choice of crystal form. The residues coordinating the surface metal ion are similar in the triclinic and monoclinic crystal forms. The coordinating ligands for the corresponding metal ion in the tetragonal crystal form are different, leading to a tighter packing arrangement. Although BacB is a monomer in solution, a dimer of BacB serves as a template on which higher order symmetrical arrangements are formed. The different crystal forms of BacB thus provide experimental evidence for metal-ion-mediated lattice formation and crystal packing. [source] | |||||||||||||||||||||||||||||||