Structure–Property Relationship of Supramolecular Ferroelectric [H‐66dmbp][Hca] Accompanied by High Polarization,Competing Structural Phases,and Polymorphs

Three polymorphic forms of 6,6′‐dimethyl‐2,2′‐bipyridinium chloranilate crystals were characterized to understand the origin of polarization properties and the thermal stability of ferroelectricity. According to the temperature‐dependent permittivity, differential scanning calorimetry, and X‐ray diffraction, structural phase transitions were found in all polymorphs. Notably, the ferroelectric α‐form crystal, which has the longest hydrogen bond (2.95 Å) among the organic acid/base‐type supramolecular ferroelectrics, transformed from a polar structure (space group, P2₁) into an anti‐polar structure (space group, P2₁/c) at 378 K. The non‐ferroelectric β‐ and γ‐form crystals also exhibited structural rearrangements around hydrogen bonds. The hydrogen‐bonded geometry and ferroelectric properties were compared with other supramolecular ferroelectrics. A positive relationship between the phase‐transition temperature (T_C) and hydrogen‐bond length (<d>) was observed, and was attributed to the potential barrier height for proton off‐centering or order/disorder phenomena. The optimized spontaneous polarization (P_s) agreed well with the results of the first‐principles calculations, and could be amplified by separating the two equilibrium positions of protons with increasing <d>. These data consistently demonstrated that stretching <d> is a promising way to enhance the polarization performance and thermal stability of hydrogen‐bonded organic ferroelectrics.     

Enhancing Intermolecular Benzoyl‐Transfer Reactivity in Crystals by Growing a “Reactive” Metastable Polymorph by Using a Chiral Additive

Racemic 2,4‐di‐O‐benzoyl‐myo‐inositol‐1,3,5‐orthoacetate, which normally crystallizes in a monoclinic form (form I, space group P2₁/n) could be persuaded to crystallize out as a metastable polymorph (form II, space group C2/c) by using a small amount of either D ‐ or L ‐ 2,4‐di‐O‐benzoyl‐myo‐inositol‐1,3,5‐orthoformate as an additive in the crystallization medium. The structurally similar enantiomeric additive was chosen by the scrutiny of previous experimental results on the crystallization of racemic 2,4‐di‐O‐benzoyl‐myo‐inositol‐1,3,5‐orthoacetate. Form II crystals can be thermally transformed to form I crystals at about 145 °C. The relative organization of the molecules in these dimorphs vary slightly in terms of the helical assembly of molecules, that is, electrophile (El)???nucleophile (Nu) and C? H???π interactions, but these minor variations have a profound effect on the facility and specificity of benzoyl‐group‐transfer reactivity in the two crystal forms. While form II crystals undergo a clean intermolecular benzoyl‐group‐transfer reaction, form I crystals are less reactive and undergo non‐specific benzoyl‐group transfer leading to a mixture of products. The role played by the additive in fine‐tuning small changes that are required in the molecular packing opens up the possibility of creating new polymorphs that show varied physical and chemical properties. Crystals of D ‐2,6‐di‐O‐benzoyl‐myo‐inositol‐1,3,5‐orthoformate (additive) did not show facile benzoyl‐group‐transfer reactivity (in contrast to the corresponding racemic compound) due to the lack of proper juxtaposition and assembly of molecules.     

Helicity Control in the Preparation of Chiral Co-crystals from Tryptamine and Achiral Carboxylic Acids by Pseudo-seeding

Abstract

Chiral crystals of tryptamine and achiral carboxylic acids such as p-chlorobenzoic acid, cinnamic acid, p-chlorocinnarnic acid and p-methylcinnamic acid were prepared by crystallization from the solutions of both components. All the crystals belonged to typical chiral space group P2₁2₁2₁. The crystal chirality is generated through the formation of a unidirectional twofold helix between the two components through quaternary ammonium salt interaction and hydrogen bonding in the lattice. This kind of spontaneous crystallization necessarily gives crystals of both clockwise and counterclockwise helicites. Here, pseudo-seeding based on utilizing these crystals as seed crystals was examined, resulting in successful helicity control in crystallization from solutions of tryptamine and different carboxylic acids.     

X‐Ray and Electron Diffraction Study of Poly(p‐dioxanone)

Summary: Solution‐grown lamellar crystals of poly(p‐dioxanone) (PPDX) have been crystallized isothermally from butane‐1,4‐diol at 100 °C. The crystal structure of PPDX has been determined by interpretation of X‐ray fiber diagrams of PPDX fibers and electron diffraction diagrams of lozenge‐shaped chain‐folder lamellar crystals. The unit cell of PPDX is orthorhombic with space group P2₁2₁2₁ and parameters: a = 0.970 nm, b = 0.742 nm, and c (chain axis) = 0.682 nm. There are two chains per unit cell, which exist in an antiparallel arrangement.

Transmission electron micrograph of PPDX chain‐folded lamellar crystals obtained by isothermal crystallization and its electron diffraction diagram.     

The nature of multiple melting transitions in cis-polyisoprene

The multiple melting transitions previously reported for cis-polyisoprene have been related to different morphological species observed in thin films using transmission electron microscopy. Two distinct types of spherulitic lamellar crystal have been identified which have characteristic growth rates, lamellar thicknesses, and fold planes. In addition to the α-lamellar crystals, which grow in prestrained films with the a axis perpendicular to the stretch direction, a second type of lamellar crystal was identified with the b axis perpendicular to the stretch direction: β-lamellae. From an analysis of the kinetics of growth and the variation of lamellar thicknesses with crystallization temperature, values of the side and surface free energies of the two types of lamellar crystal have been calculated.     

Enzymatic degradation of poly(octamethylene suberate) lamellar crystals

Enzymatic degradation of poly(octamethylene suberate) single crystals was investigated by electron microscopy. Different lamellar morphologies were obtained using 2.5-hexanediol as a solvent and at a temperature between 42 and 51 °C. Crystals with a different degree of truncation and with monolayer or bilayer organization were analyzed. Lipases from Rhizopus oryzae were found to be highly effective in degrading crystalline domains and showed different attack mechanisms. Thus, enzymes preferentially attacked the lateral crystal growth faces or the lamellar fold surfaces depending on the crystallization conditions. Temperature and indeed its fluctuation during the crystallization process were crucial to determine how degradation started and progressed. The most interesting results were obtained for single crystals characterized by a low degree of truncation and formed in crystallization baths with a small temperature oscillation. In this case, it was shown that degradation started on the folding surface of specific sectors and progressed along a preferred crystal direction.     

Ferroelectrically Switching Helical Columnar Assembly Comprising Cisoid Conformers of a 1,2,3‐Triazole‐based Liquid Crystal

The 1,2,3‐triazole molecule, which is a product of click chemistry, possesses a high dipole moment and can be a useful polar motif for ferroelectric columnar liquid crystal (LC) materials—though it has not been used to date. Herein, we report the helical assembly and ferroelectric switching properties of a columnar liquid crystal comprising a naphthalene core and 1,2,3‐triazolyl linkages. The molecule assembles into a double‐stranded helical columnar LC structure (Col_hel). The X‐ray simulations of cisoid and transoid columnar models suggest that the helical assembly comprises cisoid conformers with a non‐zero dipole moment. The helical columns in the Col_hel phase are aligned homeotropically under an electric field. The ferroelectric switching of the axial polarization can be observed in the temperature range of 105–115 °C in the Col_hel phase, wherein the triazolyl hydrogen bonding along the column axis is weakened. The ferroelectric switching event is attributed to the rotation of the polar triazolyl units in response to the electric field.     

Crystal structure and morphology of phenyl‐capped tetraaniline in the leucoemeraldine oxidation state

A series of crystals of phenyl‐capped tetraaniline in the leucoemeraldine oxidation state were obtained at different isothermal temperatures and were observed directly under transmission electron microscope. The crystals obtained at higher temperatures exhibit more perfect structures than those obtained at lower temperatures. Both the lamella thickness and the crystal size increase with crystallization temperature. The tetraaniline is apt to form larger scale crystals under lower degree of supercooling. However, their crystal structures keep steady with the crystallization temperature. The tetramer was found to adopt a monoclinic lattice with unit cell parameter of a = 13.93 Å, b = 8.82 Å, c = 23.20 Å, and β = 95.03°, as determined using electron diffraction tilting method combined with wide‐angle X‐ray diffraction experiment. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 764–769, 2006     

Morphology of polypropylene crystals. II. Twinning of lamellar crystals

Twinned crystals were obtained from fractionated isotactic polypropylene of M?_w = 600,000 by isothermal crystallization at 130°C. for 20 hr. from dilute α-chloronaphthalene solution (0.005 wt.-%). Electron microscopic observations confirm that the molecular chains of polypropylene lamellar crystals extend along the [100] direction while the folding itself occurs within the (010) planes in the monoclinic crystal form. On this basis it is shown that polypropylene forms twinned crystals in which the composition plane is the (1k0) planes. It can be deduced that the formation of twin nucleus occurs before twinning, and then growth occurs from the neighboring region of the crystal boundary by chain folding along the [100] direction.     

An isochronous decoration method for measuring linear growth rates in polymer crystals

The long spacing l of lamellar crystals of linear polyethylene increases with the crystallization temperature T_c. For low degrees of supercooling, the ratio Δl/ΔT is around 0.5 nm K^?1 for PE single crystals obtained from solution in xylene. In the restricted situation where only conduction in the crystallization vessel is involved, a heat transfer analysis shows that about 20 s is needed to change by 5 K the crystallization temperature T_c in a cylindrical vessel of 1.5 mm radius. Such rapid change of the crystallization temperature induces a sharp increase or decrease of the thickness of the single crystals. After conventional shadowing with palladium–gold alloy, the steps on the crystals are observed by conventional bright-field electron microscopy. A pioneering work was performed in this way by Bassett and Keller in 1962. Our technique allows one to determine both the shape and the dimensions of single crystals or twinned crystals of polyethylene as a function of the time of crystallization, and therefore give the quasi-instantaneous growth rates at various times.     

Self-Assembly of C3 Symmetric Rigid Macrolactams into Very Polar and Porous Trigonal Crystals

Cyclohexane and cyclotri-β-alanyl have been used as scaffolds for the design of new C₃-symmetric rings incorporating conjugated alkenes and dienes. All three C₃-symmetric lactams share the same triangular shape and their crystal system is trigonal. They all belong to the R3 space group, R3m, R3 and R3c, for the increasingly large 12-, 18- and 24-membered rigid rings, respectively. All lactams stack on top of each other, through H-bonds and van der Waals noncovalent interactions, leading to endless supramolecular cylinders and tubes. The largest member of the family leads to tubes, the central pores of which is wide enough to let water in. A common feature of all the lactams is their very large dipole, of around 9 D, according to DFT calculations. Surprisingly, all the resulting cylinders and tubes pack side by side in the crystals, with all the dipoles pointing to the same direction. As a result, all three crystals are anisotropic and appear to be the first members of a new kind of highly polar crystals.     

Crystal structures of (2-substituted-5-N-tosyl)bicyclo[3.3.0]-5-azacyclooct-2-enone: a pseudo achiral crystal from enantiopure compound and a counter-example of Wallach’s rule

An unusual crystallization affording an apparently pseudoachiral crystal from single enantiomers 1a and 1b was observed. In cases of enantiopure molecules such as 1a and 1b with structural flexibility, the tendency toward a centrosymmetric arrangement was so overwhelming that apparently achiral crystals were formed even by homochiral compounds via the formation of a pseudo-centrosymmetric asymmetric unit accompanying structural adjustment. In addition, these crystals of 1a constitute as a counter-example of Wallach’s rule.     

L-半胱氨酸自组装膜诱导草酸钙结晶研究

在CaCl2.H2O和Na2C2O4配制的过饱和溶液中,利用L-半胱氨酸(L-Cys)在金片上形成的自组装膜为模板,研究了草酸钙(CaOxa)在自组装膜上的结晶行为,并探讨了溶液pH对CaOxa晶体组成、晶型及其形貌的影响。采用X射线衍射(XRD)和扫描电子显微镜(SEM)等技术对CaOxa晶体的结构和形貌进行了表征。实验结果表明:当溶液pH=3.0时,溶液中可以形成一水草酸钙(CaC2O4.H2O,COM)和二水草酸钙(CaC2O4.2H2O,COD)晶体,而在同样pH条件下,在L-Cys自组装膜上只形成COD晶体,表明自组装单层对CaOxa晶体的成核和生长有重要影响。通过改变溶液的pH,在自组装单层上可以得到不同晶型和不同形状的CaOxa晶体。当pH=3.0时得到四方块状的COD晶体,而pH=5.0和pH=7.0时分别得到六边形和拉长六边形的COM晶体。     

Enantiomeric bis(μ‐N,N′‐hexamethylenedisalicylaldiminato)dicopper(II) complexes

The title dimeric complex, bis{μ‐2,2′‐[hexane‐1,6‐diyl­bis(nitrilo­methyl­idyne)]­diphenolato‐1:2κ⁴O,N:N′,O′}dicopper(II),[Cu₂(C₂₀H₂₂N₂O₂)₂], has been investigated by single‐crystal X‐ray diffraction, by thermogravimetric analysis and differential scanning calorimetry, and also by FT–IR spectroscopy. Different synthetic and crystallization procedures gave crystals which were quite different in appearance, and it was initially thought that these were different polymorphic forms. Subsequent structure determination showed, in fact, serendipitous preparation of crystals in the P4₁ space group by one method and in space group P4₃ by the other. In these enantiomorphic structures, the Cu atoms have a distorted flattened tetrahedral coordination, with Cu—N and Cu—O distances in the ranges 1.954 (4)–1.983 (4) and 1.887 (4)–1.903 (4) Å, respectively.     

An improved and practical approach to essentially enantiopure BINOLs: enantioselective inclusion complexation of (S)-proline

An improved and practical approach to (R)- and (S)-BINOLs has been developed. The rac-BINOL and (S)-proline were refluxed in acetonitrile for several hours, and the resulting white precipitate was recrystallized in ethanol to afford colorless crystals consisting of (S)-BINOL and (S)-proline, which were analyzed by single crystal X-ray structural analysis. Essentially enantiopure (S)- and (R)-BINOLs were obtained in high yields after decomposition of the colorless crystalline complex and evaporation of the acetonitrile mother liquor removed from the complex precipitate and successive crystallization. The (S)-proline can be recovered and reused without any decrease in efficiency.     

Morphology and structure of poly(p-dioxanone)

The morphology of solution grown single crystals of poly(p-dioxanone) was investigated. Different crystallization conditions (solvent, precipitant agent and temperature) were tested. Dendritic growth, screw dislocations and striations were observed. Crystals usually exhibited a lozenge morphology, whose apex angle changed with the crystallization conditions. In all cases, however, a single crystal electron diffraction pattern was recorded. Spherulitic morphologies were obtained by evaporation of formic acid solutions. Lamellae gave rise to well resolved electron diffraction patterns that allowed determination of the main packing characteristics. Patterns of tilted specimens helped establish an orthorhombic unit cell, whose parameters indicate a deviation from the all trans molecular conformation. Quantum mechanical calculations were performed on small model compounds to study the conformational preferences. Simulated diffraction patterns were consistent with a unit cell containing four repeat units and a P2₁2₁2₁ space group. Molecular packing suggests the existence of different kinds of folds for an assumed adjacent reentry. Polyethylene decoration hardly highlighted a crystal sectorization. Also enzymatic degradation of lamellar crystals was evaluated by using a Pseudomonas cepacia lipase.     

Crystalline Behavior and Structure of a Liquid Crystal Compound, 5‐{[4′‐(((Pentyl)oxy)‐4‐biphenylyl)carbonyl]oxy}‐1‐pentyne

Single crystals of two liquid crystal compounds, 5‐{[4′‐(((pentyl)oxy)‐4‐biphenylyl)carbonyl]oxy}‐1‐pentyne (A3EO5) and 5‐{[(4′‐nonyloxy‐4‐biphenylyl)carbonyl]oxy}‐1‐pentyne (A3EO9), have been prepared by solution growth technique. The morphologies and structures of A3EO5 and A3EO9 crystals were investigated by wide angle X‐ray diffraction (WXRD), atom force microscope (AFM) and transmission electron microscope (TEM). In contrast to the same series of compounds which have a longer alkyl tail, 5‐{[(4′‐heptoxy‐4‐biphenylyl)carbonyl]oxy}‐1‐pentyne (A3EO7), 5‐{[(4′‐heptoxy‐4‐biphenylyl)oxy]carbonyl}‐1‐pentyne (A3E′O7) and A3EO9, A3EO5 shows strikingly different crystalline behavior. The former three compounds have only one crystal form, whereas A3EO5 exhibits polymorphism. Specifically, A3EO5 crystals grown from toluene solution show two crystal forms. The first one is crystal I which adopts a monoclinic P112/m space group with unit cell parameters of a?5.79 Å, b?8.34 Å, c?43.92 Å, γ?96°, and the other one is crystal II which adopts a monoclinic P112 space group with unit cell parameters of a?5.55 Å, b?7.38 Å, c?31.75 Å, γ?94°. When using dioxane as the solvent to grow A3EO5 crystal, we can selectively obtain crystal I. A3EO5 melt‐grown crystals also have two crystal forms which derive from crystal I and crystal II, respectively. The different crystalline behavior of the compounds should correlate with their different electron dipole moment resulting from the different length of alkyl tail.     

Optical studies of the stress-induced crystallization of rubber

The low-angle light scattering by films of stretched natural and synthetic rubbers was investigated. Intense V_v scattering is found under conditions when crystallization occurs which is characteristic of the scattering from aggregates of dimensions comparable with the wavelength of visible light. These were identified with the γ fibrils described by Andrews. The dependence of scattering was studied as a function of light polarization direction, orientation direction, elongation, temperature, degree of swelling, type of swelling liquid, and degree of crosslinking. It was concluded that the scattering unit consists of an assembly of crystals with their chain axes parallel to the stretching direction, but (in the case of natural rubber at high elongations) with the fibril axis at a slight angle to the stretching direction. The scattering is not affected much by swelling but is decreased upon increasing the temperature. Upon recooling the scattering returns, but does so over several hours, indicating that much of the scattering arises from secondary crystallization.     

Laser patterning and preferential orientation of two-dimensional planar β-BaB2O4 crystals on the glass surface

The laser-induced crystallization method is applied to pattern two-dimensional planar β-BaB₂O₄ crystals on the surface of Sm₂O₃–BaO–B₂O₃ glass. By scanning Yb:YVO₄ fiber lasers (wavelength: 1080 nm) continuously with a small step (0.5 μm) between laser irradiated areas, homogeneous planar β-BaB₂O₄ crystals are patterned successfully, and a preferential growth orientation of β-BaB₂O₄ crystals is confirmed from linearly polarized micro-Raman scattering spectrum and second harmonic intensity measurements. It is found that the crystal growth direction is perpendicular to the laser scanning direction. This relation, i.e., the perpendicular relation, is different from the behavior in discrete crystal line patterning, where the crystal growth direction is consistent with the laser scanning direction. The present study proposes the possibility of the control of crystal growth direction in laser-induced crystallization in glasses.     

Identification of Molecular Crystals Capable of Undergoing an Acyl‐Transfer Reaction Based on Intermolecular Interactions in the Crystal Lattice

Investigation of the intermolecular acyl‐transfer reactivity in molecular crystals of myo‐inositol orthoester derivatives and its correlation with crystal structures enabled us to identify the essential parameters to support efficient acyl‐transfer reactions in crystals: 1) the favorable geometry of the nucleophile (? OH) and the electrophile (C?O) and 2) the molecular assembly, reinforced by C? H???π interactions, which supports a domino‐type reaction in crystals. These parameters were used to identify another reactive crystal through a data‐mining study of the Cambridge Structural Database. A 2:1 co‐crystal of 2,3‐naphthalene diol and its di‐p‐methylbenzoate was selected as a potentially reactive crystal and its reactivity was tested by heating the co‐crystals in the presence of solid sodium carbonate. A facile intermolecular p‐toluoyl group transfer was observed as predicted. The successful identification of reactive crystals opens up a new method for the detection of molecular crystals capable of exhibiting acyl‐transfer reactivity.