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New styryl dyes of the 2-benzoselenazole series which contain iodide, triiodide, and tosylate anions were synthesized. Crystals of these compounds were grown in different crystal forms – solvent free and hydroquinone, benzene or ethyl acetate solvated ones. X-ray structural studies of the crystals shows that those containing tosylate and triiodide anions form the centrosymmetrically related stacking motif, typical for styryl dye cations and favorable for [2 + 2] photocycloaddition (PCA) reactions. This reaction takes place in crystals with tosylate anions as a single crystal-to-single crystal process. On the contrary, in the triiodide dye crystals, the PCA reaction is lacking, probably due to a weak directional interaction of the selenium atoms with the anions. The iodide dye crystals demonstrate non-typical packing for styryl dyes and manifest as a two-dimensional close packing motif of the cations which is unfavorable for cycloaddition. [ABSTRACT FROM AUTHOR]

A new styryl dye of the 2-benzothiazole series which contains three methoxy groups and an iodide anion was synthesized. Three triclinic crystal forms of this dye were investigated by single crystal X-ray diffraction. All the modifications were shown to contain centrosymmetrically related stacks of cations with the syn-“head-to-tail” mutual arrangement. Stacks of cations are arranged as dimeric pairs with short interatomic distances between the ethylene group carbon atoms, d1 = 3.54–3.75 Å and significantly longer analogous distances between the adjacent pairs, d2 = 4.61–4.68 Å. The main difference of the packing consists in various orientations of N-ethyl substituents with respect to the centre of the dimer. The solid phase [2 + 2] photocycloaddition (PCA) reaction resulting in rctt isomer of the cyclobutane derivative, only proceeds in pairs where N-substituents are oriented outward from the centre of the dimeric pair. PCA is accomplished as a “single crystal-to-single crystal” transformation. [ABSTRACT FROM AUTHOR]

Crystals of molecular complexes of dimethyl sulfoxide with trichloromethane (chloroform), (CH3)2SO·2CHCl3, (I), and dichloromethane, (CH3)2SO·CH2Cl2, (II), have been grown in situ. In both compounds, the components are linked together by (Cl)C-H...O interactions. The dimethyl sulfoxide molecules in (I) are bound into chains by C-H...O interactions. In (II), pairs of the components form centrosymmetric rings, linked into a three-dimensional network by C-H...O contacts and dipole-dipole interactions between dimethyl sulfoxide molecules. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the Rh―C interactions between rhodium complexes used in catalysis and C―C bonds. The study uses the data gathered from spherical atom refinements, the high-resolution datasets based on two crystals, and the valence of deformation density. The study shows that the topological parameters of the C―C bonds are similar with the single shared-shell covalent interactions, and the two C atoms are not associated with the rhodium bonding.

The article discusses a study on the crystal and molecular structures of six diethanolamine ligands. The hydrogen bonding in each compound engaged all active hydroxy hydrogen (H) atoms. The outer surfaces of the chains are hydrophobic due to the organization of the chains. The methods used to synthesize the compounds are described.

Pyridine-3,5-dicarboxylic acid has been studied by single-crystal neutron diffraction at 15 and 296 K. Pyridine-3,5-dicarboxylic acid, in which the carboxylic acid protons have been replaced by deuterons, has also been studied at 15, 150 and 296 K. The protonated structure contains a short N⋯H⋯O hydrogen bond [N⋯O 2.523 (2) Å at 15 K]. Temperature-dependent proton migration occurs where the N—H distance in the hydrogen bond changes from 1.213 (4) Å at 15 K to 1.308 (6) Å at 300 K. In the deuterated structure the overall hydrogen-bond length increased [N⋯O 2.538 (3) Å at 15 K] and the magnitude of the migration increased so that the N—D distance changes from 1.151 (3) Å at 15 K to 1.457 (4) Å at 300 K. [ABSTRACT FROM AUTHOR]

Abstract: A new compound BiCd2AsO6 has been prepared and its crystal structure determined by single crystal X-ray diffraction. The unit cell parameters are: , and and the space group . BiCd2AsO6 is therefore noncentrosymmetric and polar. It contains seven coordinate Bi and Cd atoms, and As in AsO4 tetrahedral groups aligned in the same direction along the polar axis of the crystal. [Copyright &y& Elsevier]

A new complex, Ni(L-H) 2 , L = 3,5-dimethyl-1-thiocarboxamidopyrazole, has been synthesized and characterized by IR spectroscopy, magnetic and electrical measurements. Its crystal structure was solved from powder X-ray diffraction data. The compound crystallizes in space group with two independent half-molecules containing Ni(II) coordinated by four nitrogen atoms in a square-plane. The packing pattern consists of two stacks of parallel molecules mutually tilted at an angle of 118°. [ABSTRACT FROM AUTHOR]

The crystal structure of the iron(II) spin-crossover compound [Fe(C10H8N6)2](ClO4)2 in the high-spin state has been solved from powder X-ray diffraction data using the DASH program and refined using Rietveld refinement. The thermal spin transition has been monitored by following the change in unitcell parameters with temperature. The title compound has been found to undergo a crystallographic phase change, involving a doubling of the crystallographic a axis, on undergoing the spin transition. [ABSTRACT FROM AUTHOR]

The 1:2 adduct of benzene-1,2,4,5-tetracarboxylic acid and 4,4'-bipyridyl at 100 K has been studied by single-crystal neutron diffraction at 20, 200 and 296 K. The structure contains two short, strong N···O hydrogen bonds: one OH···N hydrogen bond [O···N 2.6104 (17) Å at 20 K] and one short N-H···O hydrogen bond [N···O 2.5220 (17),Å at 20 K]. The N-H distance in the N-H···O hydrogen bond changes from 1.207 (3) Å at 20 K to 1.302 (4) Å at 296 K and the N···O distance increases to 2.5315 (16) Å at 296 K. At 200 K the H atom lies in an intermediate position 1.251 (6) Å from the N atom with an N···O separation of 2.520 (4) Å. The O-H···N hydrogen bond, on the other hand, does not change with temperature. [ABSTRACT FROM AUTHOR]

Focuses on CSDSymmetry, a database of point-group and space-group symmetry relationships in small-molecule crystal structures. Application of an algorithm that perceives molecular symmetry to thousands of entries from the Cambridge Structural Database (CSD); Use of Microsoft Access software in adding data to the relational database, CSDSymmetry; Benefits of the inclusion of CSD reference codes.

A method for the detection of approximate molecular symmetry in crystal structures has been developed. The point-group symmetry is assigned to each molecule and the relevant symmetry elements can be visualized, superimposed on the molecule. The method has been validated against reference structures with exact symmetry subjected to small random perturbation.

The structures of four para-substituted derivatives of diphenylethynylmethanol have been determined [ditolyethynylmethanol, di(4-chloropheny)ethynylmethanol, di(4-bromophenyl)ethynylmethanol and bis(4,4'-biphenylyl)ethynylmethanol]]. The dimethyl, dichloro, dibromo and diphenyl-compounds have been analysed using X-ray diffraction at 150 K, and the dichloro compound has also been studied using neutron diffraction at 150 K. In common with the parent diphenylethynylmethanol [Garcia, Ramos, Rodriguez & Fronczek (1995). Acta Cryst. C51, 2674-2676], all four derivatives fail to form the expected strong O-H···O hydrogen bonds due to steric hindrance. Instead, the supramolecular structural organization in this family of gem-alkynols is mediated by a variety of weaker interactions. The two most acidic protons, O-H and C≡C-H, participate in weak hydrogen bonds to π-acceptors, forming synthons that stabilize all five structures. These primary interactions are reinforced by a variety of other weak hydrogen bonds involving C-H donors and the hydroxy-O as an acceptor, and by halogen···halogen interactions in the dichloro and dibromo compounds. [ABSTRACT FROM AUTHOR]

Structures of the title compounds are all mediated by strong cooperative arrangements of O-H···O hydrogen bonds, supported by a variety of weaker interactions which affect the type of O-H···O synthon that is formed. The tetrafluoro compound contains hexameric O-H···O synthons in a supramolecular chair conformation, together with C≡C-H ···F interactions. However, the tetrachloro and tetrabromo compounds both form tetrameric O-H···O synthons. This dominant pattern is supported by halogen···halogen interactions having one C-Cl[Br]···Cl[Br] angle close to 180 and the other close to 90°, and by C≡C-H···Cl[Br] interactions. [ABSTRACT FROM AUTHOR]

A single-crystal neutron diffraction study of the organic nonlinear optical material 3-(1,1-dicyanoethenyl)-1-pheny-4,5-dihydro-1H-pyrazole (hereafter DCNP), space group Cc, is presented. The study was conducted in order to relate the structural characteristics of the compound to its physical properties. DCNP exhibits a very large second harmonic generation (SHG) output, an extremely large linear electro-optical effect and photoconductive and pyroelectric properties. The nature of the hydrogen-bonding revealed by the study, in part, accounts for the first two of these phenomena. The neutron study also shows that some rather atypical stomic thermal motion is present in part of the molecule. With the aid of a variable-temperature single-crystal X-ray diffraction study, in conjunction with the neutron study, this thermal motion is attributed to libration and is fully characterized. As a result, suitable corrections to the bond geometry and the anisotropic displacement parameters of DCNP are made. The libration is also shown to enhance the SHG effect. The cell parameters from the variable-temperature X-ray study are also used in order to evaluate the thermal expansivity coefficients of DCNP. [ABSTRACT FROM AUTHOR]

The article examines the crystal structure of cyclopentanone and cyclobutanone. These compounds are described as isostructural and has two crystallographically independent molecules. The molecules located across twofold axes create antiparallel dipole-dipole dimers, while other molecules in general positions are connected together into ribbons by pairs of C--H...O interactions.

The crystal structure of isogentisin, C14H10O5, a natural product isolated from Gentiana lutea, has been determined. The phenolic ring system is essentially planar and the displacement of the methoxy substituent from the mean molecular plane is very small. The structure is stabilized by a one-dimensional chain of intermolecular hydrogen bonds. [ABSTRACT FROM AUTHOR]

Describes the crystal structure of diiodo dicarbo-closo dodecarborane. Pseudo-icosahedral cluster geometry; Intermolecular hydrogen bond; Nucleophilic role of the iodine substituents; Molecular structure; Displacement ellipsoids.

The structure of triethylammonium chloride, C6H16N+·Cl-, has been redetermined in the space group P31c. In contrast with previous refinements in the space group P63mc, no disorder of the triethylammonium cation was observed. [ABSTRACT FROM AUTHOR]

The 1:1 and 2:1 cocrystals of benzene-1,2,4,5-tetra­carboxylic acid (BTA) and 4,4′-bipyridine (BPY) have been studied using neutron diffraction at 215 and 20 K, respectively. BTA and BPY crystallize in a 1:1 ratio with 1.8 mol­ecules of water, viz. 4,4′-bipyridinium 2,5-dicarboxy­benzene-1,4-dicarboxyl­ate 1.8-hydrate, C10H12N22+·C10H4O82−·1.8H2O, (I), in the space group P , with both BTA and BPY lying on inversion centres. BTA and BPY crystallize in a 2:1 ratio, viz. 4,4′-bipyridinium bis­(2,4,5-tricarboxy­benzoate), C10H12N22+·2C10H5O8−, (II), in the space group Cc. The crystal structure of the 1:1 cocrystal contains one short N—H⋯O hydrogen bond [N⋯O = 2.6047 (19) Å] and one intra­molecular O—H⋯O hydrogen bond [O⋯O = 2.423 (3) Å]. The crystal structure of the 2:1 cocrystal contains two N—H⋯O hydrogen bonds [N⋯O = 2.639 (3) and 2.674 (2) Å], and two intra­molecular [O⋯O = 2.404 (3) and 2.420 (3) Å] and four strong inter­molecular O—H⋯O hydrogen bonds [O⋯O = 2.613 (3), 2.718 (3), 2.628 (3) and 2.739 (3) Å]. [ABSTRACT FROM AUTHOR]

4,4'-Bipyridine and 2,7-diazapyrene derivatives (A) having two ammonioalkyl N-substituents were synthesized. The complex formation of these compounds with bis(l8-crown-6)stilbene (D) was studied by spectrophotometry, cyclic voltammetry, ¹H NMR spectroscopy, and X-ray diffraction analysis. In MeCN, π-donor D and π-acceptors A form supramolecular 1:1 (D*A) and 2:1 (D*A*D) charge-transfer complexes. The D*A complexes have a pseudocyclic structure as a result of ditopic binding of the ammonium groups to the crown-ether fragments. The better the geometric matching between the components, the higher the stability of the D*A complexes (log K up to 9.39). A key driving force of the D*A*D complex formation is the excessive steric strain in the precursor D*A complexes. The pseudocyclic D*A complexes involving the ammoniopropyl derivative of 4,4'-bipyridine were obtained as single crystals. Crystallization of the related ammonioethyl derivative was accompanied by transition of the D*A complexes to a structure of the (D*A)m coordination polymer type. [ABSTRACT FROM AUTHOR]

The pressure-dependent structural evolution of a neutral zinc-imidazolate framework [Zn2(C3H3N2)4]n (Znlm) has been investigated. The as-synthesized three-dimensional Znlm network (a-phase) crystallizes in the tetragonal space group /41cd (a = 23.5028(4) Å, c= 12.4607(3) Å). The Znlm crystal undergoes a phase transition to a previously unknown β-phase within the 0.543(5)-0.847(5) GPa pressure range. The tetragonal crystal system is conserved during this transformation, and the β-phase space group is /41 (a = 22.7482(3) Å, c = 13.01 68(3) Å). The physical mechanism by which the transition occurs involves a complex cooperative bond rearrangement process. The room-temperature bulk modulus for Znlm is estimated to be ∼14 GPa. This study represents the first example of a high-pressure single- crystal X-ray diffraction analysis of a metal-organic framework. [ABSTRACT FROM AUTHOR]

The supramolecular synthon approach to crystal structure prediction (CSP) takes into account the complexities inherent in crystallization. The synthon is a kinetically favored unit, and through analysis of commonly occurring synthons in a group of related compounds, kinetic factors are implicitly invoked. The working assumption is that while the experimental structure need not be at the global minimum, it will appear somewhere in a list of computationally generated structures so that it can be suitably identified and ranked upward using synthon information. These ideas are illustrated with a set of aminophenols, or aminols. In the first stage, a training database is created of the 10 isomeric methylaminophenols. The crystal structures of these compounds were determined. The prototypes 2-, 3-, and 4-aminophenols were also included in the training database. Small and large synthons in these 13 crystal structures were then identified. Small synthons are of high topological but low geometrical value and are used in negative screens to eliminate computationally derived structures that are chemically unreasonable. Large synthons are more restrictive geometrically and are used in positive screens ranking upward predicted structures that contain these more well-defined patterns. In the second stage, these screens are applied to CSP of nine new aminols carried out in 14 space groups. In each space group, up to 10 lowest energy structures were analyzed with respect to their synthon content. The results are encouraging, and the predictions were classified as good, unclear, or bad. Two predictions were verified with actual crystal structure determinations. [ABSTRACT FROM AUTHOR]

Single crystal structures of N(CH2CH2NSiMe3)3Si-Vinyl (1) and N(CH2CH2NSiMe3)3Si-n-Butyl (2) were determined by X-ray diffraction studies: both compounds show weak transannular Nax→M interactions (1, d(Nax→Si)=2.712(1) A˚, 2, d(Nax→Ge)=2.743(3) A˚). General trends for molecular structures of the group 14 elements (Si, Ge, Sn) azametallatranes are discussed with also included DFT calculations data. [Copyright &y& Elsevier]