Crystal Molecules Research Articles

Crystal structure of bis(μ2-4-bromo-2-[({2-[({2-[(5-bromo-2-oxidobenzylidene)amino]ethyl}sulfanyl)sulfonyl]ethyl}imino)methyl]phenolato)dicopper(II) dimethylformamide disolvate.

The title dinuclear copper(II) complex [Cu2(C18H16Br2N2O4S2)2] was prepared by direct synthesis of a dianionic Schiff base derived from 5-bromo-salicyl-aldehyde and cyste-amine. The discrete mol-ecules lie across inversion centers and crystallize with two di-methyl-formamide (DMF) mol-ecules of crystallization. The unique CuII ion is four-coordinated by two tetra-dentate Schiff base ligands in a distorted square-planar N2O2 environment. In the crystal, short inter-molecular S⋯Br contacts, weak C-H⋯O hydrogen bonds and intra- and inter-molecular π-π stacking inter-actions between rings of the ligand link the components into a two-dimensional network parallel to (010).

The trans-Bis(p-thioetherphenylacetynyl)bis(phosphine)platinum(II) Ligands: A Step towards Predictability and Crystal Design.

Two organometallic ligands L1 (trans-[p-MeSC6H4C≡C-Pt(PR3)2-C≡CC6H4SMe; R = Me]) and L2 (R = Et) react with CuX salts (X = Cl, Br, I) in MeCN to form one-dimensional (1D) or two-dimensional (2D) coordination polymers (CPs). The clusters formed with copper halide can either be step cubane Cu4I4, rhomboids Cu2X2, or simply CuI. The formed CPs with L1, which is less sterically demanding than L2, exhibit a crystallization solvent molecule (MeCN), whereas those formed with L2 do not incorporate MeCN molecules in the lattice. These CPs were characterized by X-ray crystallography, thermogravimetric analysis, IR, Raman, absorption, and emission spectra as well as photophysical measurements in the presence and absence of crystallization MeCN molecules for those CPs with the solvent in the lattice (i.e., [(Cu4I4)L1·MeCN]n (CP1), [(Cu2Br2)L1·2MeCN]n (CP3), and [(Cu2Cl2)L1·MeCN]n (CP5)). The crystallization molecules were removed under vacuum to evaluate the porosity of the materials by Brunauer–Emmett–Teller (N2 at 77 K). The 2D CP shows a reversible type 1 adsorption isotherm for both CO2 and N2, indicative of microporosity, whereas the 1D CPs do not capture more solvent molecules or CO2.

Effect of elastic constants of liquid crystals in their electro-optical properties

Recently following the success of the density functional theory (DFT) in obtaining the structure and thermodynamics of homogeneous and inhomogeneous classical systems such as simple fluids, dipolar fluid and binary hard spheres, this theory was also applied to obtain the density profile of a molecular fluid in between hard planar walls by Kalpaxis and Rickayzen. In the theory of molecular fluids, the direct correlation function (DCF) can be used to calculate the equation of state, free energy, phase transition, elastic constants, etc. It is well known that the hard core molecular models play an important role in understanding complex liquids such as liquid crystals. In this paper, a classical fluid of nonspherical molecules is studied. The required homogeneous (DCF) is obtained by solving Orenstein–Zernike (OZ) integral equation numerically. Some of the molecules in the liquid crystals have a sphere shape and this kind of molecular fluid is considered here. The DCF sphere of the molecular fluid is calculated and it will be shown that the results are in good agreement with the pervious works and the results of computer simulation. Finally the electro-optical properties of ellipsoid liquid crystal using DCF of these molecules are calculated.

Crystal structure of (Z)-N-benzylidene-1-phenylmethanamine oxide hydrogen peroxide monosolvate

The title adduct, C14H13NO·H2O2, consists of (Z)-N-benzyl-idene-1-phenyl-methanamine oxide and hydrogen peroxide mol-ecules in a 1:1 ratio. The organic coformer adopts a skew geometry with an inter-aryl-ring dihedral angle of 81.9 (2)°. In the crystal, the organic and peroxide mol-ecules are linked through both peroxide O-H donor groups to oxide O-atom acceptors, giving one-dimensional chains extending along the b axis. Present also are weak inter-molecular C-H⋯O hydrogen-bonding inter-actions.

Complex free-energy landscapes in biaxial nematic liquid crystals and the role of repulsive interactions: A Wang-Landau study.

General quadratic Hamiltonian models, describing the interaction between liquid-crystal molecules (typically with D_{2h} symmetry), take into account couplings between their uniaxial and biaxial tensors. While the attractive contributions arising from interactions between similar tensors of the participating molecules provide for eventual condensation of the respective orders at suitably low temperatures, the role of cross coupling between unlike tensors is not fully appreciated. Our recent study with an advanced Monte Carlo technique (entropic sampling) showed clearly the increasing relevance of this cross term in determining the phase diagram (contravening in some regions of model parameter space), the predictions of mean-field theory, and standard Monte Carlo simulation results. In this context, we investigated the phase diagrams and the nature of the phases therein on two trajectories in the parameter space: one is a line in the interior region of biaxial stability believed to be representative of the real systems, and the second is the extensively investigated parabolic path resulting from the London dispersion approximation. In both cases, we find the destabilizing effect of increased cross-coupling interactions, which invariably result in the formation of local biaxial organizations inhomogeneously distributed. This manifests as a small, but unmistakable, contribution of biaxial order in the uniaxial phase. The free-energy profiles computed in the present study as a function of the two dominant order parameters indicate complex landscapes. On the one hand, these profiles account for the unusual thermal behavior of the biaxial order parameter under significant destabilizing influence from the cross terms. On the other, they also allude to the possibility that in real systems, these complexities might indeed be inhibiting the formation of a low-temperature biaxial order itself-perhaps reflecting the difficulties in their ready realization in the laboratory.

Symmetry Influence on the Rotation of Molecules in Crystals

It was shown that rotational mobility of molecules in crystals is affected by the symmetry of their surroundings. A hypothesis was proposed for the discovered correlation. Three cases are possible for the location of the molecules with respect to the crystallographic symmetry elements: I – the location in a general position; II – the location in special positions without symmetry disordering; III – the location in special positions with symmetry disordering. According to the experimental data, the rotation barrier heights at the location of the molecules in cases I and III are lower than in case II. This fact is explained by the amplitude and phase shifts of the rotational energy profiles of two parts of the molecule in case I and by increasing the number of minima on the rotation barrier profile at disordering the molecules by symmetry in case III. The way is proposed for lowering the rotational barrier of molecules in crystals.

Encapsulating Organic Crystals (EnOCs)

Achieving efficient capture, storage and release of small molecules is a challenge. Most materials that can harbor small molecules have been studied in the context of gas storage or separation. Formulations for hazardous reagents have only recently attracted attention, when organic compounds were discovered that encapsulate a broad range of guest molecules in crystals. Such encapsulating organic crystals (EnOCs) can suppress problematic properties of reagents and allow for controlled release in reaction mixtures. Unlike materials used for gas storage, which possess permanent porosity, their cavities are not held together by covalent or strong noncovalent interactions. Instead, EnOCs crystallize with the help of weaker packing forces. Substituted tetraaryladamantane octaethers can form high-loading inclusion compounds with reagents as guests, but they can also transition into tightly packed, solvate-free forms. Here we highlight the differences between EnOCs and known porous materials and discuss the potential of EnOCs as formulations in organic synthesis.

Crystal structures of 4-meth-oxy-benzoic acid-1,3-bis-(pyridin-4-yl)propane (2/1) and biphenyl-4,4'-di-carb-oxy-lic acid-4-meth-oxy-pyridine (1/2).

The crystal structures of two hydrogen-bonded compounds, namely 4-meth-oxy-benzoic acid-1,3-bis-(pyridin-4-yl)propane (2/1), C13H14.59N2·C8H7.67O3·C8H7.74O3, (I), and biphenyl-4,4'-di-carb-oxy-lic acid-4-meth-oxy-pyridine (1/2), C14H9.43O4·C6H7.32NO·C6H7.25NO, (II), have been determined at 93 K. In (I), the asymmetric unit consists of two crystallographically independent 4-meth-oxy-benzoic acid mol-ecules and one 1,3-bis-(pyridin-4-yl)propane mol-ecule. The asymmetric unit of (II) comprises one biphenyl-4,4'-di-carb-oxy-lic acid mol-ecule and two independent 4-meth-oxy-pyridine mol-ecules. In each crystal, the acid and base mol-ecules are linked by short O-H⋯N/N-H⋯O hydrogen bonds, in which H atoms are disordered over the acid O-atom and base N-atom sites, forming a linear hydrogen-bonded 2:1 or 1:2 unit of the acid and the base. The 2:1 units of (I) are linked via C-H⋯π, π-π and C-H⋯O inter-actions into a tape structure along [101], while the 1:2 units of (II) form a double-chain structure along [-101] through π-π and C-H⋯O inter-actions.

Tuning Luminescence and Conductivity through Controlled Growth of Polymorphous Molecular Crystals

AbstractClear structure–property correlation is of crucial importance for molecular materials for optical and electronic application. Here, a new intramolecular charge transfer compound (E)‐2‐{4‐[4‐(9H‐carbazol‐9‐yl)styryl]benzylidene}malononitrile (TCBR) with a dicyanovinyl group as the electron acceptor and a carbazole group as the electron donor is designed and synthesized. Four different single crystals based on the cis and trans isomeric forms of this compound are grown simultaneously, which are both kinetically and thermodynamically stable. The different packing modes give rise to a dynamic crystal structure change, leading to dramatically different optical and electronic properties. The closer packing can effectively promote the π–π interactions to increase the exciton coupling and orbital overlap between neighbor molecules in crystals, which produces a redshift fluorescence emission and good conductivity. This permits one to tune the packing molecules in the solid state to specific applications in a more precise way. The results of this study highlight the power of designing new functional molecules for optical and electronic applications.

Direct structural observation of the alignment and elongation in lyotropic chromonic liquid crystals under shear flow

ABSTRACTThe structural characterization of the orientation and elongation under shear flow in Lyotropic Chromonic Liquid Crystals (LCLCs) molecules, Sunset Yellow FCF (SSY), was performed by in situ rheological small/wide angle X-ray scattering (Rheo-SAXS/WAXS). The X-ray measurement results clearly demonstrated that the stacked aggregates were oriented and elongated to the shear direction under shear flow. Further shear rate increase caused the enhancement in the orientation and elongation with the inter-aggregate distance constant, and then the structural change decreased implying the onset of the orientation saturation at high shear rates.

Structural evolution during drying process in lyotropic chromonic liquid crystal

ABSTRACTThe structural evolution with the self-assembly and self-alignment progress of the typical Lyotropic Chromonic Liquid Crystals (LCLCs) molecules, Sunset Yellow FCF (SSY), was studied by time-resolved grazing-incidence wide-angle X-ray scattering (GI-WAXS). It was revealed that the SSY molecules oriented by the initial shear flow gradually assembled and was oriented by solvent evaporation. Then, the drastic progress in the assembly and orientation occurred accompanying the electrostatic interaction between the assembled aggregates.

Fabrication of vertically aligned liquid crystal cell without using a conventional alignment layer

ABSTRACTWe propose a novel method to fabricate a vertical alignment (VA) of liquid crystal (LC) molecules without using a conventional alignment layer such as polyimide film. The method produces the vertical alignment polymer layer (VAPL) by polymerisation of a monomer or mixed monomers including in the LC layer above TNI of the LC material. The VA mode LC cell with the VAPL (VAPL-LC cell) produced from the mixed monomers of acrylic acid 4-(4ʹ-octyloxy-biphenyl-4-yloxy)-butyl ester and 1,2-bis-(4-methacryloxy-phenyl)-2,2-dimethoxy-ethane-1-one exhibited enough level of alignment state and electro-optical property with high voltage holding ratio. We can expect that the VAPL-LC cell is useful for next-generation displays such as flexible liquid crystal displays because the method does not need the process including high temperature over 200°C.

INVESTIGATION OF THE INFLUENCE OF ELECTRIC FIELD ON THE ANISOTROPY OF NEMATIC LIQUID CRYSTALS BY MEANS OF X-RAY INTERFEROMETRIC METHOD

The refractive index of nematic liquid crystal (NLC) E7 in the X-ray spectral range using the X-ray interferometric method, was measured experimentally. It was shown that NLC E7 is anisotropic medium for X-rays. This method is sensitive to reorientation of the molecules of liquid crystals and allows to measure the refractive index of homogeneously aligned NLC layer, when the molecules are reoriented under the influence of external electric field.

Characterization of fluorine-centred `F...O' σ-hole interactions in the solid state.

In the current study, the crystal structure of 1-(3-nitrophenyl)-2,2,2-trifluoroethanone (A1) and (E)-4-((4-fluorophenyl) diazenyl)phenol (A2) has been analyzed for the characterization of the presence of a `unique' and `rare' intermolecular C(sp3/sp2)-F...O contact, which has been observed to play a significant role in the crystal packing. Theoretical charge-density calculations have been performed to study the nature and strength associated with the existence of this intermolecular F...O contact, wherein the F atom is attached to an sp3-hybridized C atom in the case of A1 and to an sp2 hybridized carbon in the case of A2. The crystal packing of the former contains two `electronically different' Csp3-F...O contacts which are present across and in between the layers of molecules. In the latter case, it is characterized by the presence of a very `short' (2.708 Å) and `highly directional' (168° at ∠C4-F1...O1 and 174° at ∠C10-O1...F1) Csp2-F...O contact. According to the Cambridge Structural Database (CSD) study, it is a rare example in molecular crystals. Topological features of F...O contacts in the solid state were compared with the gas-phase models. The two-dimensional and three-dimensional static deformation density obtained from theoretical multipole modeling confirm the presence of a charge depleted region on the F atoms. Minimization of the electrostatic repulsion between like charges are observed through subtle arrangements in the electronic environment in two of the short intermolecular F...O contacts. These contacts were investigated using inputs from pair energy decomposition analysis, Bader's quantum theory of atoms in molecules (QTAIM), Hirshfeld surface analysis, delocalization index, reduced density gradient (RDG) plot, electrostatic potential surface and distributed atomic polarizability. The intermolecular energy decomposition (PIXEL) and RDG-NCI (non-covalent interaction) analysis of the F...O contacts establish the interaction to be dispersive in nature. The mutual polarization of an O atom by fluorine and vice versa provides real physical insights into the role of atomic polarizability in interacting atoms in molecules in crystals.

Fabrication of homogenously self-alignment fringe-field switching mode liquid crystal cell without using a conventional alignment layer

ABSTRACTWe propose a novel method to fabricate a uniaxially homogeneous alignment of liquid crystal (LC) molecules without using a conventional alignment layer such as polyimide film. The method produces the polymer alignment layer (PAL) by polymerisation of the monomer including in the LC layer above the TNI of the LC material. The fringe-field switching (FFS) mode LC cell with the PAL (FFS-PAL-LC cell) produced from the monomer 4,4ʹ-di-mehacryloyl-oxy chalcone (4,4ʹ-DMOCh) exhibited enough level of alignment state and electro-optical property compared with the FFS-LC cell having the conventional polyimide-type alignment layer. We can expect that the FFS-PAL-LC cell is useful for next-generation displays such as flexible liquid crystal displays (LCDs) because the method does not need high-temperature process of over 200°C.

New technique shocks proteins into action

For a protein to carry out its job—whether it be replicating DNA, metabolizing fuel, transporting biomolecules, or sending cell signals—its amino acids have to move in certain ways. The patterns of these internal motions aren’t always well understood because the tools available to study them are limited. A new technique, electric field-stimulated X-ray crystallography (EF-X), combines electric pulses with time-resolved X-ray crystallography to provide more comprehensive views of the ways proteins work. Electrical charges and dipoles are present in all proteins, and external electric fields exert forces on them, causing atoms to move. In EF-X, developed by a research team led by Rama Ranganathan of the University of Texas Southwestern Medical Center, electric field pulses activate conformational changes of amino acids throughout protein molecules in crystals, and fast X-ray pulses then visualize those motions (Nature 2016, DOI: 10.1038/nature20571). Ranganathan and coworkers used EF-X to visualize motions ...

Origin and structure of polar domains in doped molecular crystals.

Doping is a primary tool for the modification of the properties of materials. Occlusion of guest molecules in crystals generally reduces their symmetry by the creation of polar domains, which engender polarization and pyroelectricity in the doped crystals. Here we describe a molecular-level determination of the structure of such polar domains, as created by low dopant concentrations (<0.5%). The approach comprises crystal engineering and pyroelectric measurements, together with dispersion-corrected density functional theory and classical molecular dynamics calculations of the doped crystals, using neutron diffraction data of the host at different temperatures. This approach is illustrated using centrosymmetric α-glycine crystals doped with minute amounts of different L-amino acids. The experimentally determined pyroelectric coefficients are explained by the structure and polarization calculations, thus providing strong support for the local and global understanding of how different dopants influence the properties of molecular crystals.

Intermolecular interactions of oligothienoacenes: Do S⋯S interactions positively contribute to crystal structures of sulfur-containing aromatic molecules?

Intermolecular interactions in the crystals of tetra- and penta-thienoacene were studied using ab initio molecular orbital calculations for evaluating the magnitude of characteristic S⋯S interactions with great attention paid to their origin. The interactions between the π-stacked neighboring molecules are significantly greater than those between the neighboring molecules exhibiting the S⋯S contact, although it has sometimes been claimed that the S⋯S interactions play important roles in adjusting the molecular arrangement of sulfur-containing polycyclic aromatic molecules in the crystals owing to short S⋯S contacts. The coupled cluster calculations with single and double substitutions with noniterative triple excitation interaction energies at the basis set limit estimated for the π-stacked and S⋯S contacted neighboring molecules in the tetrathienoacene crystal are -11.17 and -4.27 kcal/mol, respectively. Those for π-stacked molecules in the pentathienoacene crystal is -14.38 kcal/mol, while those for S⋯S contacted molecules are -7.02 and -6.74 kcal/mol. The dispersion interaction is the major source of the attraction between the π-stacked and S⋯S contacted molecules, while the orbital-orbital interactions are repulsive: The orbital-orbital interactions, which are significant for charge carrier transport properties, are not much more than the results of the short S⋯S contact caused by the strong dispersion interactions. Besides, the intermolecular interaction energy calculated for a trithienoacene dimer has strong orientation dependence.

Room-Temperature Phosphorescence of Crystalline Metal-Free Organoboron Complex.

The photoluminescence (PL) properties of a metal-free organoboron complex, bis(4-iodobenzoyl)methanatoboron difluoride (1BF2 ), were elucidated. At room temperature, 1BF2 emits blue fluorescence (FL) in nBuCl upon photoexcitation. In contrast, crystals of 1BF2 emit green PL comprised of FL and phosphorescence (PH). The room-temperature PH of crystalline 1BF2 is a consequence of 1) suppression of thermal deactivation of the S1 and T1 excited states and 2) enhancement of intersystem crossing (ISC) from the S1 to T2 or T1 . The results of X-ray crystallographic and theoretical studies supported the proposal that the former (1) is a result of intermolecular interactions caused by π-stacking in the rigid crystal packing structure of 1BF2 . The latter (2) is an effect of not only the heavy-atom effect of iodine, but also the continuous π-stacking alignment of 1BF2 molecules in crystals, which leads to a forbidden S1 →S0 transition and a small energy gap between the S1 and T2 or T1 .

1,3‐Diaryl‐β‐diketone Organic Crystals with Red Amplified Spontaneous Emission

In this study, 1-[4-(dimethylamino)phenyl]-3-(1-hydroxynaphthalen-2-yl)propane-1,3-dione (DPHND) was designed and synthesized to construct red-emissive organic solids. Although DPHND was weakly yellow fluorescent in organic solvents, its emission intensity showed a significant enhancement when a relatively large amount of poor solvent was added, and displayed typical aggregation-induced enhanced emission (AIEE). Notably, the crystals formed by a solution-diffusion approach showed bright red fluorescence (λem =621 nm), which was greatly redshifted by about 60 nm compared with that in solution. Molecules in crystals took a planar conformation and formed a herringbone packing structure, which effectively avoided π⋅⋅⋅π interactions, and hence contributed to the enhancement of the fluorescent quantum yield. The fluorescence spectrum of the long striplike crystals of DPHND gradually narrowed accompanied by a dramatic enhancement of the intensity when the pump energy of the laser beam was increased (355 nm), which indicated that these red-emissive crystals displayed typical amplified spontaneous emission (ASE). In addition, DPHND with an extended π-conjugated structure clearly improved its thermostability compared with the previously reported analogues, which may pave the way for its application in future electrically driven organic solid-state lasers.