Lithium D-Isoascorbate Monohydrate, a New Nonlinear Optical Material

Single crystals of lithium D-isoascorbate monohydrate (LDAM), (C6H7O6Li center dot H2O), are grown by a solution growth method. The crystal structure of LDAM is solved using single crystal X-ray diffraction. The space group is orthorhombic P2(1)2(1)2(1) with four formula units per unit cell and lattice parameters a = 7.7836(3) angstrom, b = 8.7456(3) angstrom, and c = 11.0368(4) angstrom. Solubility of the material in water is determined thermogravimetrically and found to have a positive temperature coefficient of solubility. Large optical quality single crystals are subsequently grown from aqueous solution by a slow cooling method. The crystal has a bulky prismatic habit and among the prominent faces the c face appears as the only principal morphological face. The crystal exhibits a (010) cleavage. Dielectric spectroscopy reveals a nearly Debye type Cole-Cole behavior with anisotropy in relaxation. Optical transmission range is found to be from 300 to 1400 nm. The principal refractive indices of this biaxial crystal, measured using Brewster's angle method, at wavelengths 405, 543, and 632.8 nm, show high dispersion. The crystal is negative biaxial with 2V(z) = 107.8 degrees (405 nm) and belongs to the Hobden class 3. Theoretically generated type 1 and type 2 second order phase matching curves match very well with the experimental results. The second-order nonlinear coefficient d(14) was determined to be 7 x 10(-13) m/V. For the optimum phase matching direction (type 2), the second-order effective nonlinear coefficient and the walk off angle are determined to be 0.84 times d(14) and 3.5 degrees respectively. The crystal possesses high multiple surface damage thresholds of 18 GW/cm(2) and 8 GW/cm(2) at laser wavelengths 1064 and 532 nm, respectively.

Crystal Structures and Physicochemical Properties of Four New Lamotrigine Multicomponent Forms

In the present study, four new multicomponent forms of lamotrigine (LTG) with selected carboxylic acids, viz. acetic acid, propionic acid, sorbic acid, and glutaric acid, have been identified. Preliminary solid-state characterization was done by differential scanning calorimetry/thermogravimetric, infrared, and powder X-ray diffraction techniques. X-ray single-crystal structure analysis confirmed the proton transfer, stoichiometry, and the molecular composition, revealing all of these to be a new salt/salt-cocrystal/salt monosolvate monohydrate of LTG. All four compounds exhibited both the aminopyridine dimer of LTG (motif 4) and cation-anion dimers between protonated LTG and the carboxylate anion in their crystal structures. Further, these new crystal forms were subjected to solubility studies in water, powder dissolution studies in 0.1 N HCl, and stability studies under humid conditions in comparison with pure LTG base. The solubility of these compounds in water is significantly enhanced compared with that of pure base, which is attributed to the type of packing motifs present in their crystal structures as well as to the lowering of the pH by the acidic coformers. Solid residues of all forms remaining after solubility and dissolution experiments were also assessed for any transformation in water and acidic medium.

The Role of Weak Interactions in the Phase Transition and Distinct Mechanical Behavior of Two Structurally Similar Caffeine Co-crystal Polymorphs Studied by Nanoindentation

Although weak interactions, such as C-H center dot center dot center dot O and pi-stacking, are generally considered to be insignificant, it is their reorganization that holds the key for many a solid-state phenomenon, such as phase transitions, plastic deformation, elastic flexibility, and mechanochromic luminescence in solid-state fluorophores. Despite this, the role of weak interactions in these dynamic phenomena is poorly understood. In this study, we investigate two co-crystal polymorphs of caffeine:4-chloro-3-nitrobenzoic acid, which have close structural similarity (2D layered structures), but surprisingly show distinct mechanical behavior. Form I is brittle, but shows shear-induced phase instability and, upon grinding, converts to Form II, which is soft and plastically shearable. This observation is in contrast to those reported in earlier studies on aspirin, wherein the metastable drug forms are softer and convert to stable and harder forms upon stressing To establish a molecular level understanding, have investigated the two co-crystal polymorphs I and II by single crystal X-ray diffraction, nanoindentation to quantify mechanical properties, and theoretical calculations. The lower hardness (from nanoindentation) and smooth potential surfaces (from theoretical studies) for shearing of layers in Form II allowed us to rationalize the role of stronger intralayer (sp(2))C-H center dot center dot center dot O and nonspecific interlayer pi-stacking interactions in the structure of II. Although the Form I also possesses the same type of interactions, its strength is clearly opposite, that is, weaker intralayer (sp(3))C-H center dot center dot center dot O and specific interlayer pi-stacking interactions. Hence, Form I is harder than Form IL Theoretical calculations and indentation on (111) of Form I suggested the low resistance of this face to mechanical stress; thus, Form I converts to II upon mechanical action. Hence, our approach demonstrates the usefulness of multiple techniques for establishing the role of weak noncovalent interactions in solid-state dynamic phenomena, such as stress induced phase transformation, and hence is important in the context of solid-state pharmaceutical chemistry and crystal engineering.

A Donor-Acceptor-Donor Structured Organic Conductor with S center dot center dot center dot S Chalcogen Bonding

A novel thiophene derivative 7,9-di(thiophen-2-yl)-8H-cyclopentaa]acenaphthylen-8-one (DTCPA) is shown to exhibit high electrical conductivity (1.97 x 10(-2) +/- 0.0018 S/cm at RT) in the crystalline state. The material shows two orders of increase in conductivity from normal solid to single crystalline state. The crystal structure has S center dot center dot center dot S chalcogen bonding, C-H center dot center dot center dot O hydrogen bonding, and pi center dot center dot center dot pi stacking as the major intermolecular interactions. The nature and strength of the S center dot center dot center dot S interactions in this structure have been evaluated by theoretical charge density analysis, and its contribution to the crystal packing quantified by Hirshfeld surface analysis. Further, thermal and morphological characterizations have been carried out, and the second harmonic generation (SHG) efficiency has been measured using the Kurtz-Perry method.

Evolution of Nanocrystalline Ba2NaNb5O15 in 2BaO-0.5Na(2)O-2.5Nb(2)O(5)-4.5B(2)O(3) Glass System and Its Refractive Index and Band Gap Tunability

Monophasic Ba2NaNb5O15 was crystallized at nanometer scale (12-36 nm) in 2BaO-0.5Na(2)O-2.5Nb(2)O(5)- 4.5B(2)O(3) glass system. To begin with, optically transparent glasses, in this system, were fabricated via the conventional melt. quenching technique. The amorphous and glassy characteristics of the as-quenched samples were respectively confirmed by X-ray powder diffraction and differential thermal analyses. Nearly homogeneous distribution of Ba2NaNb5O15 (BNN) nanocrystals associated with tungsten bronze structure akin to their bulk parent structure was accomplished by subjecting the as-fabricated glasses to appropriate heat-treatment temperatures. Indeed transmission electron microscopy (TEM) carried out on these samples corroborated the presence of Ba2NaNb5O15 nanocrystals dispersed in a continuous glass matrix. The as-quenched glasses were similar to 75% transparent in the visible range of the electromagnetic spectrum. The optical band gap and refractive index were found to have crystallite size (at nanoscale) dependence. The optical band gap increased with the decrease in crystallite size. The refractive indices of the glass nanocrystal composites as determined by Brewster angle method were rationalized using different empirical models. The refractive index dispersion with wavelength of light was analyzed on the basis of the Sellmeier relations. At room temperature under UV excitation (355 nm) these glass nanocrystal composites displayed violet-blue emission which was ascribed to the defects states.

Combinatorial Exploration of the Structural Landscape of Acid-Pyridine Cocrystals

The structural landscape of acid-pyridine cocrystals is explored by adopting a combinatorial matrix method with 4-substituted benzoic acids and 4-substituted pyridines. The choice of the system restricts the primary synthon to the robust acid-pyridine entity. This methodology accordingly provides hints toward the formation of secondary synthons. The pK(a) rule is validated in the landscape by taking all components of the matrix together and exploring it as a whole. Along with the global features, the exploration of landscapes reveals some local features. Apart from the identification of secondary synthons, it also sheds light on the propensity of hydration in cocrystals, synthon competition, and certain topological similarities. The method described here combines two approaches, namely, database analysis and high throughput crystallography, to extract more information with minimal extra experimental effort.

Mechanochemical Synthesis of Amide Functionalized Porous Organic Polymers

Two porous organic polymers decorated with the amide functionality were synthesized mechanochemically and their properties were compared with the ones prepared by conventional solution mediated method. All the POPs were subjected to gas and water vapor sorption studies. The mechanochemically synthesized POPs have less surface area and show moderate adsorption properties compared to the solution mediated POPs. The amide based POPs show remarkable stability in water and concentrated acids.

Magnetism and superconductivity in Sb-doped binary and ternary iron chalcogenide single crystals

We report the single crystal growth of antimony doped Fe1+yTe and Fe1+yTe0.5Se0.5 (Fe1+ySbxTe1-x (x=0, 2%, 5%) and Fe1+yTe0.49Se0.49Sb0.02) by a modified horizontal Bridgman method. Growth parameters are optimized to obtain high quality single crystals. The antiferromagnetic (AFM) transition at T-N = 62.2 K which is a first order transition, shifts to lower temperature on doping in Fe1+yTe. Alternately when the chalcogen site of the ternary compound Fe1+yTe0.5Se0.5 is doped with Sb, superconductivity is preserved albeit the superconducting transition temperature (T-C) falls slightly and a concomitant reduction occurs in superconducting volume fraction. (C) 2013 Elsevier B.V. All rights reserved,

Exploring the Crystal Structure Landscape with a Heterosynthon Module: Fluorobenzoic Acid:1,2-Bis(4-pyridyl)ethylene 2:1 Cocrystals

The crystal structure landscape of the 2:1 benzoic acid:dipyridylethylene cocrystal (BA:DPE-I) is explored experimentally with fluoro-substituted benzoic acids and extended with studies employing the Cambridge Structural Database (CSD). The interpretation of the cocrystal landscape is facilitated by considering the kinetically favored and robust acidpyridine heterosynthon as a modular unit. Information based on high-throughput crystallography shows that polymorphs and pseudopolymorphs may belong to the same landscape but arise from different crystallization pathways because of complex and different kinetic features, and secondary synthon preferences. Using the CSD as a guide, the coformer was changed from 1,2-bis(4-pyridyl)ethylene (DPE-I) to 1,2-bis(4-pyridyl)ethane (DPE-II) and this provides an extended interpretation of the BA:DPE-I cocrystal landscape, also highlighting the complexity of the kineticthermodynamic dichotomy during the molecule-to-crystal progression.

Building upon Supramolecular Synthons: Some Aspects of Crystal Engineering

It has been 20 years since the concept of supramolecular synthon was introduced with the purpose of rational supramolecular synthesis. While this concept has been greatly successful in employing a retrosynthetic approach in crystal engineering, the past few years have seen a continuous evolution of supramolecular synthons from being a synthetic subunit to a basic unit for understanding the dynamics of crystallization. This review attempts to give a glimpse of such developments.

Synthesis of ZnO nanorods on a flexible Phynox alloy substrate: influence of growth temperature on their properties

A novel flexible alloy substrate (Phynox, 50 mm thick) was used for the synthesis of zinc oxide (ZnO) nanorods via a low-temperature solution growth method. The growth of ZnO nanorods was observed over a low temperature range of 60-90 degrees C for a growth duration of 4 hours. The as-synthesized nanorods were characterized using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) for their morphology, crystallinity, microstructure and composition. The as-grown ZnO nanorods were observed to be relatively vertical to the substrate. However, the morphology of the ZnO nanorods in terms of their length, diameter and aspect ratio was found to vary with the growth temperature. The morphological variation was mainly due to the effects of the various relative growth rates observed at the different growth temperatures. The growth temperature influenced ZnO nanorods were also analyzed for their wetting (either hydrophobic or hydrophilic) properties. After carrying out multiple wetting behaviour analyses, it has been found that the as-synthesized ZnO nanorods are hydrophobic in nature. The ZnO nanorods have potential application possibilities in self-cleaning devices, sensors and actuators as well as energy harvesters such as nanogenerators.

Reconciling results of MOCVD of a CNT composite with equilibrium thermodynamics

Composition and microstructure of the composite films can be tailored by controlling the CVD process parameters if an appropriate model can be suggested for quantitative prediction of growth. This is possible by applying equilibrium thermodynamics. A modification of such standard modeling procedure was required to account for the deposition of a hybrid film comprised of carbon nanotubes (CNTs), metallic iron (Fe), and magnetite (Fe3O4), a composite useful for energy storage. In contrast with such composite nature of the deposits obtained by inert-ambient CVD using Fe(acac)3 as precursor, equilibrium thermodynamic modeling with standard procedure predicts the deposition of only Fe3C and carbon, without any co-deposition of Fe and Fe3O4. A modification of the procedure comprising chemical reasoning is therefore proposed herein, which predicts simultaneous deposition of FeO1-x, Fe3C, Fe3O4 and C. At high temperatures and in a carbon-rich atmosphere, these convert to Fe3O4, Fe and C, in agreement with experimental CVD. Close quantitative agreement between the modified thermodynamic modeling and experiment validates the reliability of the modified procedure. Understanding of the chemical process through thermodynamic modeling provides potential for control of CVD process parameters to achieve desired hybrid growth. (C) 2016 Elsevier B.V. All rights reserved.

Optical Diagnostic and Modeling Solution Growth Process of Sodium Chlorate Crystals

Both a real time optical interferometric experiment and a numerical simulation of two-dimension non-steady state model were employed to study the growth process of aqueous sodium chlorate crystals. The parameters such as solution concentration distribution, crystal dimensions, growth rate and velocity field were obtained by both experiment and numerical simulation. The influence of earth gravity during crystal growth process was analyzed. A reasonable theory model corresponding to the present experiment is advanced. The thickness of concentration boundary layer was investigated especially. The results from the experiment and numerical simulation match well.

Growth of bulk single crystals beta-FeSi2 by chemical vapour deposition

Bulk single crystals b-FeSi2, as a new photoelectric and thermoelectric material, has been successfully grown using chemical vapor transport technique by using iodine as transport agent in a sealed ampoule. The effects of crystal growth condition on quality and morphologies of the single crystals were studied. Both needle-like and grain-like single crystals were gained. By changing substrate temperature, tetrahedral high quality a-FeSi2 single crystals were also obtained.

Numerical simulation of magnetic field design for damping thermocapillary convection in a floating half-zone

The magnetic fields produced by electrical coils are designed for damping the the thermocapillary convection in a floating half-zone in microgravity. The fields are designed specially to reduce the flow near the free surface and then in the melt zone by adjusting the longitudinal coil positions close to the melt zone. The effects of the designed magnetic fields on reducing the flow velocity and temperature distribution non-uniformity in the melt zone are stronger than those of the case of an uniform longitudinal magnetic field obtained by numerical simulation, particularly at the melt-rod interface. It brings fundamental insights into the heat and mass transfer control at the solidification interface by the magnetic field design for crystal growth by the floating full-zone method.