Supramolecular architecture in the crystals of polyfluorinated homophthalic acids

X-ray diffraction analysis of four perfluorinated homophthalic (2-carboxymethylbenzoic) acids is carried out. In the crystals of 2-carboxymethyl-3,4,5,6-tetrafluorobenzoic acid (1) the chains (1D architecture) form with the usual dimeric carboxylic C(O)OH

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O(HO)C synthon. The aromatic carboxylic group is disordered in the ratio 0.58:0.42 over two positions. In the crystals of 2-(carboxydifluoromethyl)-3,4,5,6-tetrafluorobenzoic (2) and 2-(1-carboxy-2,2,2-trifluoroethyl)-3,4,5,6-tetrafluorobenzoic acids (3) the layers (2D architecture) with dimeric and chain-like synthons C(O)OH...O(HO)C are found. In the crystals of 2-[methoxycarbonyl(difluoromethyl)]-3,4,5,6-tetrafluorobenzoic acid (4) only dimers (0D architecture) form with the chain synthon that incorporates both an ester and a carboxylic group. In the crystals of 1 and 2 intermolecular H-O...π interactions, in the crystals of 4 C-F...π interactions, and in 3 both types of interactions are observed.

     

Crystalline Morphology and Polymorphic Phase Transitions in Electrospun Nylon 6 Nanofibers

Uniform nylon 6 nanofibers with diameters around 200 nm were prepared by electrospinning. Polymorphic phase transitions and crystal orientation of nylon 6 in unconfined (i.e., as-electrospun) and a high T(g) (340 degrees C) polyimide confined nanofibers were studied. Similar to melt-spun nylon 6 fibers, electrospun nylon 6 nanofibers also exhibited predominant, meta-stable gamma crystalline form, and the gamma-crystal (chain) axes preferentially oriented parallel to the fiber axis. Upon annealing above 150 degrees C, gamma-form crystals gradually melted and recrystallized into the thermodynamically stable alpha-form crystals, which ultimately melted at 220 degrees C. Release of surface tension accompanied this melt-recrystallization process, as revealed by differential scanning calorimetry. For confined nanofibers, both the melt-recrystallization and surface tension release processes were substantially depressed; gamma-form crystals did not melt and recrystallize into alpha-form crystals until 210 degrees C, only 10 degrees C below the T(m) at 220 degrees C. After complete melting of nano-confined crystals at 240 degrees C and recrystallization at 100 degrees C, only alpha-form crystals oriented perpendicular to the nanofiber axis were obtained. In the polyimide-confined nanofibers, the Brill transition (from the monoclinic alpha-form to a high temperature monoclinic form) was observed at 180-190 degrees C, which was at least 20 degrees C higher than that in unconfined nylon 6 at approximately 160 degrees C. This, again, was attributed to the confinement effect.     

Semiorganic nonlinear optical material for frequency doubling: preparation and properties of sodium p-nitrophenolate dihydrate (SPNP)

Sodium p-nitrophenolate (SPNP), a semiorganic nonlinear optical (NLO) material useful for frequency doubling in the IR region, has been synthesized. The solubility studies have been carried out in the temperature range 30-50 degrees C. Single crystals (size 12 mmx7 mmx4 mm) have been grown by slow evaporation of the saturated aqueous solution (methanol as solvent) at 30 degrees C. The lattice parameters of the grown crystals have been determined by single crystal X-ray diffraction technique. The UV-vis-NIR transmittance spectrum has been recorded in the range 200-1500 nm. The molecular structure was confirmed by FT-IR and FT-NMR. SPNP was thermally stable up to 103 degrees C as determined by TG/DTA curves. By a modified Kurtz and Perry method, the powder SHG efficiency was found to be five times that of KDP and its phase matching property was established. Laser damage threshold of SPNP was determined using a Nd:YAG laser.     

Single crystal x-ray diffraction study of dioxane,pyrazine, and pyridine complexes of 3-(1-amino-2,2,2-trifluoroethylidene)-2-imino-1,1,4,5,6,7-hexafluoroindan

Single crystals of complexes of 3-(1-amino-2,2,2-trifluoroethylidene)-2-imino-1,1,4,5,6,7-hexafluoroindan (1) with 1,4-dioxane, pyrazine, and pyridine have been synthesized. Their structure was investigated by X-ray analysis. In crystals of the dioxane complex, compound 1 is present together with its tautomer — 2-amino-3-(1-imino-2,2,2-trifluoroethyl)-1,1,4,5,6,7-hexafluoroindene (1a), and these compounds are in an equilibrium ratio of ～60:40. Gas-phase quantum chemical calculations have been performed to examine the possibility of a tautomeric equilibrium of enaminoimine 1 in the corresponding complexes.     

Molecular compasses and gyroscopes with polar rotors: synthesis and characterization of crystalline forms

We report the highly convergent synthesis and solid-state characterization of six crystalline "molecular compasses" consisting of a central phenylene rotor with polar substituents, or compass needle, and two trityl groups axially connected by acetylene linkages to the 1,4-positions. Compounds with fluoro-, cyano-, nitro-, amino-, diamino-, and nitroamino substituents are expected to emulate the parent compound which was shown to form crystals where the central phenylene can rotate about its 1,4-axis with rate constants in the 10(3) -10(6) s(-)(1) dynamic ranges near ambient temperature, depending on crystal morphology. With data from single-crystal X-ray diffraction analysis, solid-state CPMAS (13)C NMR, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA), it is shown that a relatively small structural perturbation by a single polar group (F, CN, NO(2), NH(2)) results in isomorphous structures with analogous properties. In analogy to the parent compound, crystals grown from benzene formed clathrate structures in the space group Ponemacr; with one molecular compass and two benzene molecules per unit cell. Solvent-free crystals with the same space group obtained by a first-order phase transition between 60 and 130 degrees C were shown to be spectroscopically identical to those obtained by slow solvent evaporation from a mixture of CH(2)Cl(2) and hexanes. A qualitative analysis of the positionally disordered phenylene groups in terms of the expected solid-state rotational dynamics suggests a nonsymmetric, 2-fold rotational potential, or a process involving full 360 degrees turns.     

Synthesis and characterization of new hexahelicene derivatives

The synthesis and structural characterization of a new hexahelicene derivative 2 is reported. This compound features a new type of structure bearing a bromine atom and a methoxy group. Suitable crystals of the latter indicate that its conformation closely resembles that of the unsubstituted [6]helicene, whose idealized symmetry is C2. This 3-bromo-14-methoxyhexahelicene was subjected to lithiation/phosphinilation and yielded the new 3-methoxy-14-(diphenylphosphino)hexahelicene 3.     

In situ crystallization of low-melting ionic liquids

Single crystals of five very low-melting ionic liquids, [emim]BF4 (mp -1.3 degrees C), [bmim]PF6 (+1.9 degrees C), [bmim]OTf (+6.7 degrees C), [hexpy]NTf2 (-3.6 degrees C), and [bmpyr]NTf2 (-10.8 degrees C), have been grown using a combined calorimetric and zone-melting approach and their crystal structures determined by X-ray diffraction.     

Theoretical study on the characterization of the ribosyl C4'-radical observed in irradiated crystals of uridine

The angular dependence of the β-hydrogens hyperfine splitting (hfs) constants of the 1′amino 2′-deoxyribosyl C4′-radical (1) has been computed at the B3LYP/6-311G**//UHF/6-31G** level for the S-type (C2′endo ring puckering) and N-type (C3′endo ring puckering) configurations. Good agreement between the theoretical hfs constants and the three large experimental β-hydrogen hfs constants of the radical species observed in irradiated single crystals of uridine has been found only for the N-type configuration with the β5′-oxygen in the staggered conformation. It is concluded that the observed radical species is the uridine C4′-radical (2) that adopts the C3′ endo ring puckering as found in single crystals of uridine by means of neutron diffraction. This conclusion is in contrast with that reached in a previous theoretical study.     

Microscopic Fourier Transform Infrared Characterization on Two Types of Spherulite with Polymorphic Crystals in Poly(heptamethylene terephthalate)

FTIR microspectrometry with in situ temperature variation and IR‐peak‐mapping capability, and POM characterization were used to study the crystal distribution in dual spherulites in poly(heptamethylene terephthalate). By tracing the crystalline IR bands of the α‐crystal and β‐crystal to get the crystal distribution, the techniques resolve that the ringed and ringless spherulites comprise α‐ and β‐crystals, respectively. In addition, temperature‐dependent IR analyses on the spots related to the two crystals also reveal the α‐ and β‐crystals melt at 98 and 104 °C, respectively. The ringed and ringless spherulites were proven to be correlated with the α‐ and β‐crystal forms, respectively.

     

Polymorphism in Br2 clathrate hydrates

The structure and composition of bromine clathrate hydrate has been controversial for more than 170 years due to the large variation of its observed stoichiometries. Several different crystal structures were proposed before 1997 when Udachin et al. (Udachin, K. A.; Enright, G. D.; Ratcliffe, C. I.; Ripmeester, J. A. J. Am. Chem. Soc. 1997, 119, 11481) concluded that Br2 forms only the tetragonal structure (TS-I). We show polymorphism in Br2 clathrate hydrates by identifying two distinct crystal structures through optical microscopy and resonant Raman spectroscopy on single crystals. After growing TS-I crystals from a liquid bromine-water solution, upon dropping the temperature slightly below -7 degrees C, new crystals of cubic morphology form. The new crystals, which have a limited thermal stability range, are assigned to the CS-II structure. The two structures are clearly distinguished by the resonant Raman spectra of the enclathrated Br2, which show long overtone progressions and allow the extraction of accurate vibrational parameters: omega(e) = 321.2 +/- 0.1 cm(-1) and omega(e)x(e) = 0.82 +/- 0.05 cm(-1) in TS-I and omega(e) = 317.5 +/- 0.1 cm(-1) and omega(e)x(e) = 0.70 +/- 0.1 cm(-1) in CS-II. On the basis of structural analysis, the discovery of the CS-II crystals implies stability of a large class of bromine hydrate structures and, therefore, polymorphism.     

Thermodynamic and kinetic thermal analyses on dual crystal forms in polymorphic poly(heptamethylene terephthalate)

Thermal analyses were performed for determining the equilibrium melting temperatures T of the respective α‐ and β‐crystal in melt‐crystallized polymorphic poly(heptamethylene terephthalate) (PHepT) using both linear and nonlinear Hoffman‐Weeks (H‐W) methods for comparison of validity. These two crystals in PHepT do not differ much in their melting temperatures. The equilibrium melting temperatures of the α‐ and β‐crystal as determined by the linear H‐W method are 98 °C and 100.1 °C, respectively; but the nonlinear H‐W method yielded higher values for both crystals. The equilibrium melting temperatures of the α‐ and β‐crystal according to the nonlinear H‐W method are 121 °C and 122.5 °C, respectively. Both methods consistently indicate that T of the β‐crystal is only slightly higher than that of the α‐crystal. Such small difference in T between the α‐ and the β‐crystal causes difficulties in judging the relative thermodynamic stability of these two crystals. Thus, kinetics of these two crystals was compared using the Avrami and Ozawa theory. The crystallization produced by quenching from T_max = 110 °C and 150 °C shows a heterogeneous and homogeneous nucleation mechanism, respectively. The lower T_max = 110 °C leads to heterogeneous nucleation and only α‐crystal in PHepT, whose crystallization rates at same T_c are much higher than crystallization rates by quenching from T_max = 150 °C leading to either α‐ or β‐crystal with homogeneous nucleation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1839–1851, 2009     

Über die Reindarstellung des Bromchlorids und dessen Verhalten in Acetonitril

The Preparation of Pure Bromine Chloride and on its Behaviour in Acetonitrile. Pure bromine chloride has successfully been prepared from bromine and chlorine. The bromine was quantitatively chlorinated in solution of difluordichlormethane with a large exess of chlorine at ?79°C under irradiation with U.V. light. The bromine chloride so obtained was removed from equilibrium by precipitation under cooling to ?120 to ?110°C. The solvent and the exess chlorine then were destillad at the same temperature under high vacuum, the system being detached from vacuum as soon as the residue was dry. Using a temperature difference of 1°, the orange-coloured crystalline powder could bee sublimated at ?79°C, the resulting beautiful, orange-coloured crystals (m. p. ?56,5°C) being completely stable in a trap at ?79°C. In acetonitrile as solvent, bromine chloride is stable even at room temperature because of the formation of an adduct with the solvent. In these solutions exists the ionic equilibrium 2 BrCl_solv?Br + BrCl.     

Quantitative thermodynamic analysis of sublimation rates using an atomic force microscope

Atomic force microscopy (AFM) has been successfully used to study the activation energy for evaporation of pentaerythritol tetranitrate (PETN) nanoislands formed by spin coating. These islands are annealed isothermally in the temperature range of 30-70 degrees C for a given time and are scanned with AFM in contact mode at room temperature. The volume of these islands does not change significantly up to about 35-40 degrees C indicating that sublimation is not significant below 40 degrees C. Above 40 degrees C, the islands start shrinking, and the rate of weight loss is analyzed as a function of temperature. The activation energy of evaporation using AFM was found to be similar to that for bulk PETN crystals using thermogravimetric analysis (TGA) at higher temperatures (110-135 degrees C). These results demonstrate that AFM is a useful tool to measure thermodynamic properties with a nanoscale probe.     

Nonspherical ZnS colloidal building blocks for three-dimensional photonic crystals

The asymmetry introduced by a complex or nonspherical basis promotes photonic band gap formation in three-dimensional photonic crystals. However, relatively few techniques have been demonstrated to produce uniform nonspherical colloids for use as photonic crystal bases. Here we expand the menu of basis types with high refractive index by preparing nonspherical zinc sulfide colloids of uniform size and shape. Dimers, trimers, and planar tetramers were precipitated from aqueous solution by the thermal decomposition of thioacetamide in the presence of zinc nitrate, manganese nitrate, and nitric acid. The well-defined morphological types were obtained from suspensions aged for 4-6 h at 26-32 degrees C and then for 20-35 min at 85 degrees C. Stereological techniques were used to analyze SEM images and determine the percentage of each particle class. For example, the quantitative characterization of a particle population prepared at 29 degrees C for 6 h and 85 degrees C for 22 min had the composition 59+/-3% spheres, 31+/-2% dimers, 7+/-1% trimers, 0.4+/-0.2% tetramers, and 2.5+/-0.8% complex clusters (encompasses all other varieties of shape). X-ray diffraction and X-ray photoelectron spectroscopy confirmed the zinc blend crystal structure and the stoichiometric composition of the particles. The refractive index was estimated as 2.25 (413 nm) -2.09 (709 nm) by fitting experimental absorption spectra to curves derived from Mie scattering calculations. This indicated an average porosity approximately 24%. Such colloids offer the potential to form diamond-like lattices with large, stable photonic band gaps.     

Formation of Metal-Related Ions in Matrix-Assisted Laser Desorption Ionization

In a study of the metal-related ion generation mechanism in matrix-assisted laser desorption ionization (MALDI), crystals of matrix used in MALDI were grown from matrix- and salt-containing solutions. The intensities of metal ion and metal adducts of the matrix ion obtained from unwashed crystals were higher than those from crystals washed with deionized water, indicating that metal ions and metal adducts of the matrix ions are mainly generated from the surface of crystals. The contributions of preformed metal ions and metal adducts of the matrix ions inside the matrix crystals were minor. Metal adducts of the matrix and analyte ion intensities generated from a mixture of dried matrix, salt, and analyte powders were similar to or higher than those generated from the powder of dried droplet crystals, indicating that the contributions of the preformed metal adducts of the matrix and analyte ions were insignificant. Correlation between metal-related ion intensity fluctuation and protonated ion intensity fluctuation was observed, indicating that the generation mechanism of the metal-related ions is similar to that of the protonated ions. Because the thermally induced proton transfer model effectively describes the generation of the protonated ions, we suggest that metal-related ions are mainly generated from the salt dissolution in the matrix melted by the laser.

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Graphical Abstract ?

     

Surface Fixing Effect of Vacuum Evaporated Particles on Polyethylene Single Crystals

Summary: The recrystallization behavior of high density polyethylene (HDPE) single crystals with vacuum evaporated metal chromium or carbon on their surface has been investigated by transmission electron microscopy (TEM) and electron diffraction (ED) techniques. The results indicate that the particle‐coated HDPE single crystals can retain their single crystal structure after complete melting and subsequent recrystallization, with the heat‐treated temperature as high as 200 °C. This phenomenon is attributed to a surface fixing effect of vacuum evaporated Cr or carbon on the single crystals.

A bright‐field electron micrograph and the corresponding electron diffraction pattern of recrystallized Cr‐coated HDPE single crystals.     

Observations on Solution Crystallization of Poly(vinyl alcohol) in the Presence of Single‐Wall Carbon Nanotubes

PVA/SWNT dispersions yield aloe plant‐like crystals, where the leaves are single crystals templated by PVA coated SWNT. Longer growth times (≈18 months) lead to hexagonal rod‐like crystals. HR‐TEM images show evidence that PVA molecules are aligned parallel to the SWNT axis. WAXD, electron diffraction, and HR‐TEM observations of these aloe plant and hexagonal crystals suggests evidence for possible PVA‐SWNT epitaxy. Wide‐angle and electron diffraction data of these crystals also show that the structure seems to mimic the 2D hexagonal crystal packing of SWNT. PVA lattice images and moiré fringes were also observed in the leaf‐like crystals.

     

Supramolecular architecture of crystals of perfluorinated 3-alkylphthalides

The molecular and crystal structures of perfluoro-3-alkylphthalides (3-hydroxyperfluoro-3-methylphthalide and its hydrate, two polymorphs of 3-hydroxyperfluoro-3-ethylphthalide and 3-hydroxyperfluoro-3-isopropylphthalide) are determined by single crystal X-ray diffraction. In the crystals, the supramolecular O–Н…O=C synthon occurs leading, except the crystallohydrate, to the formation of C₁¹ (6) hydrogen bonded chains (supramolecular 1D motifs). According to the DFT/M06-2X/TZV calculations, the interaction energy of hydrogen bonded molecular pairs increases in this series, which can be explained by additional C=O…π, O…π, and C–F…π interactions.     

X-ray diffraction investigation of perfluoro-4-methylenecyclohexa-2,5-dienones

Perfluorinated 8-phenyl-7,8-diethylbicyclo[4.2.0]octa-1,4,6-trien-3-one (3), 2-(4-oxocyclohexa-2,5-dienylidene)-1,1-diethylbenzocyclobutene (4) and 2-(4-oxocyclohexa-2,5-dienylidene)-5-(2-phenyl-cis-1,2-diethylbenzocyclobuten-1-yloxy)-1,1-diethylbenzocyclobutene (5), including the 4-methylencyclohexa-2,5-dienone fragment, were prepared by the reaction of perfluoro-1,1-(1) and-1,2-diethylbenzocyclobutene (2) with pentafluorobenzene in SbF₅. Single crystal X-ray diffraction study of compounds 3–5 revealed that the oxygen atom of the C=O group participated in the formation of supramolecular architectures in all three compounds, and C=O…π bonding may be considered as the corresponding synthon (with increased separation in the case of compound 5). C-F…π bonding acts as a second synthon. F…F interactions in crystals 3–5 were classified as stabilizing or enforced.     

Synthesis and liquid crystal properties of phthalocyanine bearing a star polytetrahydrofuran moiety

A new polymeric ligand, 6-(3,4-dicyanophenylthio)-hexyl-2-polytetrahydrofuranacetate (2) and its liquid crystalline polymeric phthalocyanine, 2,9,16,23-tetrakis-{6-(polytetrahydrofuran-2-carboxylate)-hexylthio-phthalocyaninatocobalt(II) (3), {Co[Pc(S-C₆H₁₃OCO-poly-THF)₄]}(CoPcLC) have been synthesized. The ligand and the phthalocyanine, bearing polytetrahydrofuran moieties (poly-THF), were characterized using elemental analysis, FTIR, ¹H and ¹³C NMR, and UV–Vis techniques. CoPcLC (3) promotes a greater interaction between the mesogens, resulting in solution aggregations together with a red-shift in the Q-band in the presence of the soft Ag⁺ ion. The dielectric anisotropy and phase transition temperature values of CoPcLC doped with 4-cyano-4′-n-pentylbiphenyl (5CB) were found to be 7.17 and 40.5 °C, respectively. The dielectrical anisotropy behaviour of the liquid crystals changes from the positive to the negative type. The current–voltage characteristics of the liquid crystals show a non-linear behaviour.