Crystal structure and computational studies of N-((2-ethoxynaphthalen-1-yl)methylene)-4-fluoroaniline

The Schiff base compound, N-((2-ethoxynaphthalen-1-yl)methylene)-4-fluoroaniline, has been synthesized and characterized by X-ray diffraction method. The title compound, C19H16FNO, crystallizes in triclinic, space group P-1 (no. 2), a = 10.6343(9) Å, b = 11.4720(10) Å, c = 13.8297(13) Å, α = 102.466(7)°, β = 104.763(7)°, γ = 98.972(7)°, V = 1552.7(2) Å3, Z = 4, T = 293(2) K, μ(MoKα) = 0.086 mm-1, Dcalc = 1.255 g/cm3, 24355 reflections measured (3.16° ≤ 2Θ ≤ 51°), 5779 unique (Rint = 0.0794, Rsigma = 0.0696) which were used in all calculations. The final R1 was 0.0373 (I > 2σ(I)) and wR2 was 0.0763 (all data). The title compound contains two molecules with a similar structure in the asymmetric unit cell. The packing of the crystal structure is determined by weak C–H···F and C-H···N intermolecular hydrogen bonds. The contributions of these weak interactions in the crystal structure were calculated by the Hirshfeld surfaces and examined by the intermolecular interactions within the structure. The existence, nature and percentage contribution of different intermolecular interactions H···H, C···H, N···H, and F···H were determined using Hirshfeld surface analysis and fingerprint plots.

4-Phenylnaphtho[2,3-c]furan-1(3H)-one, 9-Phenylnaphtho[2,3-c]furan-1(3H)-one and 3a,4-Dihydro-9-phenylnaphtho[2,3-c]furan-1(3H)-one Crystal Structures

The crystal structures are reported for two unsubstituted arylnaphthalene lactones, 4-phenylnaphtho[2,3-c]furan-1(3H)-one (2), 9-phenylnaphtho[2,3-c]furan-1(3H)-one (3) and a non-aromatic dihydro arylnaphthene lactone, 3a,4-dihydro-9-phenylnaphtho[2,3-c]furan-1(3H)-one (5). There are only minor differences in the geometrical parameters of these structures. However, in certain cases, both isomers of arylnaphthalene lactones (termed Type I and Type II) were found in the same asymmetric unit cell.

Laser generation on weak modes in graphene structure with asymmetric unit cell

Problem formulating. Lasing on strong («radiative») plasmon resonance mode in graphene structure with dual grating gate with asymmetric unit cell requires strong gain. It is possible to achieve lasing in a weak ("non-radiative") mode at a lower gain rate. Goal. Theoretical study of laser generation on weak plasmonic resonance mode in single layer graphene structure screened by dual grating gate with asymmetric unit cell. Result. Laser generation on weak plasmonic resonance mode in single layer graphene structure screened by dual grating gate with asymmetric unit cell is reached. Excitation of a weak plasmon resonance mode requires less gain than excitation of a radiative one. Practical meaning. Results can be used to create sources of terahertz waves.

Structural Transformations in Crystals Induced by Radiation and Pressure. Part 7. Molecular and Crystal Geometries as Factors Deciding about Photochemical Reactivity under Ambient and High Pressures

We studied the photochemical reactivity of salts of 4-(2,4,6-triisopropylbenzoyl)benzoic acid with propane-1,2-diamine (1), methanamine (2), cyclohexanamine (3), and morpholine (4), for compounds (1), (3), and (4) at 0.1 MPa and for compounds (1) and (2) at 1.3 GPa and 1.0 GPa, respectively. The changes in the values of the unit cell parameters after UV irradiation and the values of the intramolecular geometrical parameters indicated the possibility of the occurrence of the Norrish–Yang reaction in the case of all the compounds. The analysis of the intramolecular geometry and free spaces revealed which o-isopropyl group takes part in the reaction. For (1), the same o-isopropyl group should be reactive at ambient and high pressures. In the case of (2), high pressure caused the phase transition from the space group I2/a with one molecule in the asymmetric unit cell to the space group P1¯ with two asymmetric molecules. The analysis of voids indicated that the Norrish–Yang reaction is less probable for one of the two molecules. For the other molecule, the intramolecular geometrical parameters showed that except for the Norrish–Yang reaction, the concurrent reaction leading to the formation of a five-membered ring can also proceed. In (3), both o-isopropyl groups are able to react; however, the bigger volume of a void near 2-isopropyl may be the factor determining the reactivity. For (4), only one o-isopropyl should be reactive.

M 4Au12Ag32(p-MBA)30 (M = Na, Cs) bimetallic monolayer-protected clusters: synthesis and structure

Crystals of M 4Au12Ag32(p-MBA)30 bimetallic monolayer-protected clusters (MPCs), where p-MBA is p-mercaptobenzoic acid and M + is a counter-cation (M = Na, Cs) have been grown and their structure determined. The molecular structure of triacontakis[(4-carboxylatophenyl)sulfanido]dodecagolddotriacontasilver, Au12Ag32(C7H5O2S)30 or C210H150Ag32Au12O60S30, exhibits point group symmetry 3 at 100 K. The overall diameter of the MPC is approximately 28 Å, while the diameter of the Au12Ag20 metallic core is 9 Å. The structure displays ligand bundling and intermolecular hydrogen bonding, which gives rise to a framework structure with 52% solvent-filled void space. The positions of the M + cations and the DMF solvent molecules within the void space of the crystal could not be determined. Three out of the five crystallographically independent ligands in the asymmetric unit cell are disordered over two sets of sites. Comparisons are made to the all-silver M 4Ag44(p-MBA)30 MPCs and to expectations based on density functional theory.

Crystal structures of sodium-, lithium-, and ammonium 4,5-dihydroxybenzene-1,3-disulfonate (tiron) hydrates

The solid-state structures of the Na+, Li+, and NH4 + salts of the 4,5-dihydroxybenzene-1,3-disulfonate (tiron) dianion are reported, namely disodium 4,5-dihydroxybenzene-1,3-disulfonate, 2Na+·C6H4O8S2 2−, μ-4,5-dihydroxybenzene-1,3-disulfonato-bis[aqualithium(I)] hemihydrate, [Li2(C6H4O8S2)(H2O)2]·0.5H2O, and diammonium 4,5-dihydroxybenzene-1,3-disulfonate monohydrate, 2NH4 +·C6H4O8S2 2−·H2O. Intermolecular interactions vary with the size of the cation, and the asymmetric unit cell, and the macromolecular features are also affected. The sodium in Na2(tiron) is coordinated in a distorted octahedral environment through the sulfonate oxygen and hydroxyl oxygen donors on tiron, as well as an interstitial water molecule. Lithium, with its smaller ionic radius, is coordinated in a distorted tetrahedral environment by sulfonic and phenolic O atoms, as well as water in Li2(tiron). The surrounding tiron anions coordinating to sodium or lithium in Na2(tiron) and Li2(tiron), respectively, result in a three-dimensional network held together by the coordinate bonds to the alkali metal cations. The formation of such a three-dimensional network for tiron salts is relatively rare and has not been observed with monovalent cations. Finally, (NH4)2(tiron) exhibits extensive hydrogen-bonding arrays between NH4 + and the surrounding tiron anions and interstitial water molecules. This series of structures may be valuable for understanding charge transfer in a putative solid-state fuel cell utilizing tiron.

aCHESYM: standardized placement of macromolecular models in the unit cell

Unique choice of the unit cell and the asymmetric unit are well defined and described in the International Tables for Crystallography vol. A. Unfortunately, the placement of molecules within the unit cell is not standardized. Since structure solution programs often use random numbers in their algorithms, the selected set of atomic coordinates may be different even with successive runs of the same program. Although formally correct, an arbitrary choice of molecular placement within the unit cell is confusing and may lead to interpretation errors [1]. With the use of the anti-Cheshire unit cell introduced by Dauter [2], for all space groups without inversion symmetry, it is possible to transform the molecular model such that its center of gravity falls within the anti-Cheshire asymmetric unit cell. It means that for macromolecular crystal structures it should be possible to standardize the placement of the molecules within the unit cell. In consequence, it should be easier for crystallographers and non-crystallographers to compare similar or related crystal structures. An implementation of the anti-Cheshire concept has been programmed in Python as a web service, aCHESYM. The aCHESYM program takes a PDB file as input and transforms the macromolecular model into the desired anti-Cheshire region. The program can also handle structure factor CIF files if the transformation used requires reindexing of the reflection data. The unit cell, coordinates and displacement parameters of all atoms after transformation are saved in a new PDB file. All the calculated transformations are reversible, so there is no danger of data loss. Moreover, the program helps the user to find the most compact assembly of the molecules (chains) in the structure when there are several chains in the asymmetric unit.