Chiral Crystal Structure Research Articles

Paintable band-edge liquid crystal lasers

In this paper we demonstrate photonic band-edge laser emission from emulsion-based polymer dispersed liquid crystals. The lasing medium consists of dye-doped chiral nematic droplets dispersed within a polymer matrix that spontaneously align as the film dries. Such lasers can be easily formed on single substrates with no alignment layers. The system combines the self-organizing periodic structure of chiral nematic liquid crystals with the simplicity of the emulsion procedure so as to produce a material that retains the emission characteristics of band-edge lasers yet can be readily coated. Sequential and stacked layers demonstrate the possibility of achieving simultaneous multi-wavelength laser output from glass, metallic, and flexible substrates.

Structural studies on different types of ferroelectric liquid crystalline substances

Structural studies on different types of ferroelectric liquid crystalline substances Structural studies of ferroelectric liquid crystalline substances of different molecular structure have been reviewed. The discussion of the results deals mainly with the structure of chiral liquid crystals forming the smectic mesophase with ferroelectric order, as the research on ferroelectric liquid crystals, due to their high potential for application in electro-optics and photonics, has recently become one of the most attractive fields. Based on data of polarizing optical microscopy and X-ray diffraction obtained for unoriented samples we have identified the type of the mesophases, the temperature of the phase transitions and outlined the phase diagrams. An analysis of the relation between the molecular conformation and different types of phase transitions has been performed. The layer spacing and the average intermolecular distances have been determined for all studied phases from the positions of the small and the large angle diffraction peaks, respectively.

Spontaneous Resolution of Enantiomers by Crystallization: Insights from Computed Crystal Energy Landscapes

We used crystal structure prediction methods to generate racemic and homochiral crystal structures of benzo(c)phenanthrene, 3,4-dehydroproline anhydride, and 2,6-dimethylglycoluril, which are all known to spontaneously resolve. The known homochiral crystal structures were found at or near the global minimum in lattice energy; however, in all three cases there were hypothetical racemic crystal structures within a few kJ mol−1 in energy. The comparison of hypothetical racemic structures with the known homochiral crystal structures showed structural similarities, despite the symmetry differences, suggesting that most molecules are very unlikely to crystallize in a chiral crystal structure that is markedly more stable than any racemic crystal. Thus the experimentally observed asymmetry in the thermodynamic favorability of racemic and homochiral crystal structures is not due to experimental bias; that is, any thermodynamic drive for spontaneous resolution is genuinely small. Hence, whereas the formation of a r...

Solvent Induced Pseudopolymorphism in a Calixarene-Based Porous Host Framework

The self-assembly properties of the proximal p-tert-butylcalix[4]dihydroquinone compound have been studied to investigate the role played by crystallization conditions in driving the formation of a previously reported cubic porous framework. In chloroform and anhydrous ethyl acetate, the mutual inclusion of the tert-butyl groups is favored, leading to the cubic porous structure; otherwise, in the presence of a higher water amount, the OH groups provide H-bonds with bridging water molecules and a new triclinic crystal structure is obtained, in which the calixarene molecules include chloroform inside their cavities. By exposing a cubic/triclinic powder mixture to acetonitrile vapors, a new monoclinic chiral crystal structure is obtained by supramolecular assembly of calixarene, acetonitrile, and water molecules with the formation of single handed helices.

Poly[bis(μ2-2-aminopyrazine-κ2N1:N4)(μ2-nitrato-κ2O:O)(nitrato-κ2O,O′)disilver(I)]: an achiral two-dimensional coordination polymer forming chiral crystals

The solution reaction of AgNO(3) and 2-aminopyrazine (apyz) in a 1:1 ratio gives rise to the title compound, [Ag(2)(NO(3))(2)(C(4)H(5)N(3))(2)](n), (I), which possesses a chiral crystal structure. In (I), both of the crystallographically independent Ag(I) cations are coordinated in tetrahedral geometries by two N atoms from two apyz ligands and two O atoms from nitrate anions; however, the Ag(I) centers show two different coordination environments in which one is coordinated by two O atoms from two different symmetry-related nitrate anions and the second is coordinated by two O atoms from a single nitrate anion. The crystal structure consists of one-dimensional Ag(I)-apyz chains, which are further extended by mu(2)-kappa(2)O:O nitrate anions into a two-dimensional (4,4) sheet. N-H...O and C(apyz)-H...O hydrogen bonds connect neighboring sheets to form a three-dimensional supramolecular framework.

Two regioisomers of condensed thioheterocyclic triazine synthesized from 6-phenyl-3-thioxo-2,3,4,5-tetrahydro-1,2,4-triazin-5-one

In the crystal structure of 6-phenyl-3-thioxo-2,3,4,5-tetrahydro-1,2,4-triazin-5-one, C(9)H(7)N(3)OS, (I), the 1,2,4-triazine moieties are connected by face-to-face contacts through two kinds of double hydrogen bonds (N-H...O and N-H...S), which form planar ribbons along the a axis. The ribbons are crosslinked through C-H...pi interactions between the phenyl rings. The molecular structures of two regioisomeric compounds, namely 6-phenyl-2,3-dihydro-7H-1,3-thiazolo[3,2-b][1,2,4]triazin-7-one, C(11)H(9)N(3)OS, (II), and 3-phenyl-6,7-dihydro-4H-1,3-thiazolo[2,3-c][1,2,4]triazin-4-one, C(11)H(9)N(3)OS, (III), which were prepared by the condensation reaction of (I) with 1,2-dibromoethane, have been characterized by X-ray crystallography and spectroscopic studies. The crystal structures of (II) and (III) both show two crystallographically independent molecules. While the two compounds are isomers, the unit-cell parameters and crystal packing are quite different and (II) has a chiral crystal structure.

Chiral supramolecular chemistry crystal structure synthesis - constructing channel structures based onD3metal complexes

Chiral supramolecular chemistry crystal structure synthesis - constructing channel structures based on<i>D</i>₃metal complexes

Dipyridinium dichromate: an achiral compound forming chiral crystals

The title compound, (C(5)H(6)N)(2)[Cr(2)O(7)], crystallizes in one of the Sohncke space groups, viz. P2(1)2(1)2(1). Crystallization of dipyridinium dichromate is thus an example of spontaneous formation of a chiral crystal structure from achiral molecules. The dichromate anion adopts a virtually eclipsed achiral conformation, and the crystal structure is held together primarily by N-H...O and C-H...O interactions. The possibility of using dipyridinium dichromate as a reagent in enantioselective synthesis is discussed.

The hydrogen-bonding patterns of 3-phenylpropylammonium benzoate and 3-phenylpropylammonium 3-iodobenzoate: generation of chiral crystals from achiral molecules

The crystal structures and hydrogen-bonding patterns of 3-phenylpropylammonium benzoate, C(9)H(14)N(+) x C(7)H(5)O(2)(-), (I), and 3-phenylpropylammonium 3-iodobenzoate, C(9)H(14)N(+) x C(7)H(4)IO(2)(-), (II), are reported and compared. The addition of the I atom on the anion in (II) produces a different hydrogen-bonding pattern to that of (I). In addition, the supramolecular heterosynthon of (II) produces a chiral crystal packing not observed in (I). Compound (I) packs in a centrosymmetric fashion and forms achiral one-dimensional hydrogen-bonded columns through charge-assisted N-H...O hydrogen bonds. Compound (II) packs in a chiral space group and forms helical one-dimensional hydrogen-bonded columns with 2(1) symmetry, consisting of repeating R(4)(3)(10) hydrogen-bonded rings that are commonly observed in ammonium carboxylate salts containing chiral molecules. This hydrogen-bond pattern, which has been observed repeatedly in ammonium carboxylate salts, thus provides a means of producing chiral crystal structures from achiral molecules.

A Simple and Novel Route for The Preparation of Chiral Sodium Zincophosphate

AbstractA simple and novel route for the preparation of chiral sodium zincophosphate (NaZnPO4·H2O) (CZP) was studied, and the target product was obtained with Na3PO4·12H2O and ZnSO4·7H2O as raw materials and polyethylene glycol‐400 (PEG‐400) as a surfactant via one step low heat solid state reaction. The product was characterized with TG/DTG, XRD, TEM and SEM. The experimental results showed that the NaZnPO4·H2O, which was all obtained from different P/Zn atomic ratios (0.9–1.15) of Na3PO4·12H2O to ZnSO4·7H2O and different ageing time (2.0–8.0 h) at 60 °C, had the same chiral crystal structures except slight difference in their crystallinity. The comparison experimental results suggest that the ageing temperature and anion control the enantiomorphism of NaZnPO4·H2O, that is, if ZnSO4·7H2O or Zn(NO3)2·6H2O were used as Zn source, the first chiral structure of space group P6122 was formed when the reaction mixture was aged at 60 °C, and the second chiral structure of space group P6522 was got when the reaction mixture was aged at room temperature.

Enantioselective Intramolecular Cyclopropanation of cis‐Alkenes by Chiral Ruthenium(II) Schiff Base Catalysts and Crystal Structures of (Schiff Base)Ruthenium Complexes Containing Carbene, PPh3, and CO Ligands.

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2-[3-Dicyanomethylene-2-(3-methoxybenzylidene)indan-1-ylidene]malononitrile

The title compound, C23H12N4O, has potential application in non-linear optics; it has a chiral crystal structure despite the lack of a stereogenic centre. The crystal structure involves two intermolecular C—H...N hydrogen bonds.

Crystal Structure and Thermochemical Properties of a First Scandium Borophosphate, Sc(H2O)2[BP2O8]·H2O

Crystalline samples of scandium borophosphate, Sc(H2O)[BP2O8]·H2O, were synthesized hydrothermally from acidic suspensions of scandium sesquioxide and boric and phosphoric acid at 443 K. The chiral crystal structure (space group P6522 (No. 179), a = 957.52(3) pm, c = 1581.45(6) pm, Z = 6) was solved from single-crystal data and contains helical chain anions of alternating borate and phosphate tetrahedra interconnected by ScO4(H2O)2 coordination octahedra. On thermal treatment, a reversible release of the hydrate water from the structural channels is observed, and rehydation appears as soon as the compound is exposed to air moisture for at least 1 day. X-ray powder diffractions show that the structure is retained during the de-/rehydration process. Both the crystal structure of the dehydrated phase, Sc(H2O)2[BP2O8] (a = 953.5(1) pm, c = 1576.8(2) pm), and that of the rehydrated phase, which is identical to the hydrothermal product, were refined from X-ray powder data with Rietveld methods. When the dehydrated phase is exposed to an ammonia atmosphere, NH3 absorption is observed.

Defect modes in a stacked structure of chiral photonic crystals

An optical propagation simulation is carried out for the study of photonic defect modes in a stacked structure of cholesteric liquid crystal films with spatially varying pitch. The defects are introduced by a pitch jump and a phase jump in the cholesteric helix. The effect of a finite sample thickness on transmission of the defect mode and on the required polarization of incident light to create the defect mode is discussed. For normal and near-normal incidence of circularly polarized light with the same handedness as structure, the defect caused by a pitch jump results in discrete peaks within a forbidden band in the transmission. The particular spectrum is similar to the feature of a Fabry-Pérot interferometer. By introducing an additional phase jump, linear blueshifts of the defect modes in transmission spectra are correlated with an increase in the twist angle.

Broad Stopband Characteristic of Dielectric Chiral Photonic Crystals

In this paper, a novel chiral photonic crystal structure is presented. The formula of reflection coefficient of multi-layer chiral media is applied to dielectric-chiral photonic crystal structure, which is composed of thin chiral layers sandwiched by conventional media. To compare with previous literature, we consider the dielectric structure with alternate glass and GaAs layers. The power reflectance as a function of wavelength for this photonic crystal structure has been calculated. The results are in good agreement with that of Reference. However, our method is simpler. From these graphs, it is found that 100% reflectance is only in finite wavelength ranges, and reflection bandwidth is also small for conventional photonic crystal structure. For chiral photonic crystal, the results show that the chiral photonic band gap (PBG) structure gives nearly 100% reflections in the near-infrared region in addition to some parts of the visible region of the wavelengths. Therefore, it can be used as a broadband reflector and filter.

The Mirror of Galadriel: looking at chiral and achiral crystal structures

Illustrative examples are provided of infrequent situations arising in the chiral or achiral crystal structures formed of chiral or achiral molecules. For absolute-configuration determination by way of structure analysis, it is demonstrated how powerful characterization of enantiomers by way of CD spectra and enantioselective chromatography can be when working on the single crystal used in the diffraction analysis. Common misunderstandings in the description of non-centrosymmetric achiral crystal structures are clarified. Further attention is given to questions of nomenclature.

One-dimensional chiral photonic band gap structure analyzed by non-symmetric transmission-line method

In this paper, the formula of reflection coefficient of multi-layer chiral media is derived by non-symmetric transmission-line method. Then, it is applied to one-dimensional (1-D) chiral photonic crystal structure, which is composed of thin chiral layers sandwiched by air. The results show that it is difficult to obtain photonic band gap for general dielectric when the contrast of two media refractive indices is not large, and the reflection coefficient is small. However, for chiral photonic crystal, although the refractive index of chiral layer is small, the wave spectrum contains forbidden zones and the reflection coefficient from such a structure is found to be almost equal to 1, i.e., the wave is almost totally reflected through adjusting chiral parameter. Therefore it is easier to obtain an ideal photonic band gap.

The Mirror of Galadriel: looking at chiral and achiral crystal structures

Illustrative examples are provided of infrequent situations arising in the chiral or achiral crystal structures formed of chiral or achiral molecules. For absolute-configuration determination by way of structure analysis, it is demonstrated how powerful characterization of enantiomers by way of CD spectra and enantioselective chromatography can be when working on the single crystal used in the diffraction analysis. Common misunderstandings in the description of non-centrosymmetric achiral crystal structures are clarified. Further attention is given to questions of nomenclature.

Photoinduced chemical reactions on natural single crystals and synthesized crystallites of mercury(II) sulfide in aqueous solution containing naturally occurring amino acids.

Photoirradiation at >300 nm of aqueous suspensions of several natural crystal specimens and synthesized crystallites of mercury(II) sulfide (HgS) induced deaminocyclization of optically active or racemic lysine into pipecolinic acid (PCA) under deaerated conditions. This is the first example, to the best of our knowledge, of photoinduced chemical reactions of natural biological compounds over natural minerals. It was found that the natural HgS crystals had activity higher than those of synthesized ones but lower than those of other sulfides of transition metals, e.g., CdS and ZnS, belonging to the same II-IV chalcogenides. In almost all of the photoreactions, decompostion of HgS occurred to liberate hydrogen sulfide (H(2)S) and Hg(2+), and the latter seemed to have undergone in-situ reductive deposition on HgS as Hg(0) after a certain induction period (24-70 h) during the photoirradiation, as indicated by the darkened color of the suspensions. The formation of PCA, presumably through combination of oxidation of lysine and reduction of an intermediate, cyclic Schiff base, could also be seen after a certain induction time of the Hg(0) formation. This was supported by the fact that the addition of small amount of Hg(2+) (0.5 wt % of HgS) increased the PCA yield by almost 2-fold. We also tried to elucidate certain aspects of the plausible stereochemical reactions in relation to the chiral crystal structure of HgS. Although, in some experiments, slight enantiomeric excess of the product PCA was observed, the excess was below or equal to the experimental error and no other supporting analytical data could not be obtained; we cannot conclude the enantiomeric photoproduction of PCA by the natural chiral HgS specimen.

Chiral Smectic C Structures of Virus-Based Films

Long-range ordered virus-based films were fabricated using M13 phages (viruses) which were aligned and assembled using the meniscus phenomena. Their ordered structures and morphologies were studied and characterized using polarized optical microscopy (POM), atomic force microscopy (AFM), and scanning electron microscopy (SEM). M13 virus particles which are 880 nm in length were the basic building block of the fabricated films. Due to the unique micrometer length scale of viruses, the smectic ordering of virus particles could be easily visualized using conventional microscopy techniques and compared with a theoretical model of chiral liquid crystal structures. From the results of POM, AFM, and SEM, the viral films were determined to have a chiral smectic C structure. By a comparison of the ordering of film formation as a function of virus concentration and the formation of bundle-like domain structure found in viral thin films, a mechanism of film formation is suggested. These virus-based film structures are organized on multiple length scales, easily fabricated, and allow integration of aligned semiconductor and magnetic nanocrystals. These self-assembled hybrid materials may have applications in miniaturized self-assembled electronic devices.