Shortest Crystallographic Axis Research Articles

Crystal structure and Hirshfeld surface analysis of 2,6-di-iodo-4-nitro-toluene and 2,4,6-tri-bromo-toluene.

The title compounds, 2,6-di-iodo-4-nitro-toluene (DINT, C7H5I2NO2) and 2,4,6-tri-bromo-toluene (TBT, C7H5Br3,), are tris-ubstituted toluene mol-ecules. Both mol-ecules are planar, only the H atoms of the methyl group, and the nitro group in DINT, deviate significantly from the plane of the benzene ring. In the crystals of both compounds, mol-ecules stack in columns up the shortest crystallographic axis, viz. the a axis in DINT and the b axis in TBT. In the crystal of DINT, mol-ecules are linked via short N-O⋯I contacts, forming chains along [100]. In TBT, mol-ecules are linked by C-H⋯Br hydrogen bonds, forming chains along [010]. Hirshfeld surface analysis was used to explore the inter-molecular contacts in the crystals of both DINT and TBT.

Charge-Stripe Order and Superconductivity in Ir1\u2212xPtxTe2

A combined resistivity and hard x-ray diffraction study of superconductivity and charge ordering in Ir Ir1−xPtxTe2, as a function of Pt substitution and externally applied hydrostatic pressure, is presented. Experiments are focused on samples near the critical composition xc ~ 0.045 where competition and switching between charge order and superconductivity is established. We show that charge order as a function of pressure in Ir0.95Pt0.05Te2 is preempted — and hence triggered — by a structural transition. Charge ordering appears uniaxially along the short crystallographic (1, 0, 1) domain axis with a (1/5, 0, 1/5) modulation. Based on these results we draw a charge-order phase diagram and discuss the relation between stripe ordering and superconductivity.

Hydrogen-bonded structures and interaction energies in two forms of the SGLT-2 inhibitor sotagliflozin.

The sotagliflozin molecule exhibits two fundamentally different molecular conformations in form 1 {systematic name: (2S,3R,4R,5S,6R)-2-[4-chloro-3-(4-ethoxybenzyl)phenyl]-6-(methylsulfanyl)tetrahydro-2H-pyran-3,4,5-triol, C21H25ClO5S, (I)} and the monohydrate [C21H25ClO5S·H2O, (II)]. Both crystals display hydrogen-bonded layers formed by intermolecular interactions which involve the three -OH groups of the xyloside fragment of the molecule. The layer architectures of (I) and (II) contain a non-hydrogen-bonded molecule-molecule interaction along the short crystallographic axis (a axis) whose total PIXEL energy exceeds that of each hydrogen-bonded molecule-molecule pair. The hydrogen-bonded layer of (I) has the topology of the 4-connected sql net and that formed by the water and sotagliflozin molecules of (II) has the topology of a 3,7-connected net.

Intermolecular interactions and unexpected isostructurality in the crystal structures of the dichlorobenzaldehyde isomers

The crystal structures of the six dichlorobenzaldehyde isomers, four of them newly determined, are analyzed in terms of the geometry and energies of their intermolecular interactions, quantified using the semi-classical density sums (SCDS-PIXEL) method. A consistent feature in all six structures is molecular stacks propagating along a short crystallographic axis of ca 3.8 Å. The stacks have a closely comparable geometry in each isomer, but the interaction energies between stacked molecules are variable on account of the differing relative positions of the Cl substituents. In the majority of the isomers the stacking interactions are the most stabilizing in the structure. Exceptions are the 2,4- and 3,5-isomers, where more stabilizing interactions are made between stacks. In general, the most stabilizing non-stacking intermolecular interactions in the structures are those involving C-H...O contacts. Observed motifs based on Cl...Cl interactions appear to be largely imposed by the constraints of other more stabilizing intermolecular interactions. The isomeric series displays the following noteworthy features: (i) the 2,3- and 2,6-isomers are isostructural despite having different orientations of the Cl and aldehyde functionalities; (ii) the 2,5-isomer exhibits whole-molecule disorder; (iii) the 2,5- and 3,5-isomers have more than one molecule in the crystallographic asymmetric unit (Z' > 1). These features in particular are considered on the basis of the intermolecular interaction energies.

A new parameter for classification of polycyclic aromatic hydrocarbon crystalline motifs: a Hirshfeld surface investigation

The classical crystalline motif categorizations of polycyclic aromatic hydrocarbons (PAHs) have gained interest as of late as it was discovered that the “defining” crystallographic axis was not always the “shortest crystallographic axis” as previously defined and that systems under pressure would exhibit a motif's typical axis length but not its typical interplanar angle (θ). Here we use Hirshfeld surfaces to investigate the relative percent of intermolecular close contact interactions existing within the four established crystalline PAH motifs under ambient and high pressures. It was discovered that the fraction of C⋯C interactions (C⋯C%) coupled with θ could ultimately define the structural motifs. A new parameter, the pi-degree parameter (π°), which relates the amount of π⋯π interaction to the interplanar angle, was developed as a function of θ and C⋯C% in order to unambiguously categorize PAH motifs. A new motif, beta-herringbone (β-HB), defining a subset of PAH structures with σ-bound aromatic groups is defined. The new motif parameter was then used to investigate several high pressure and low temperature PAH structures and provided unambiguous motif categorization regardless of the “shortest crystallographic axis”, temperature, or pressure.

Thermodynamic Modelling of Ferromagnetic Shape Memory Actuators

We present a thermodynamic Gibbs free energy model for the finite element simulation of the coupled thermo-magneto-mechanical behavior of ferromagnetic shape memory alloys (FSMAs). Starting from a free energy model for the conventional shape memory effect, additional terms are included to take into account the magnetic anisotropy and the geometry-dependent magnetostatic energy. Different functions are considered for the strain dependence of the anisotropy energy in order to describe the experimentally found strong dependence of the anisotropy energy on the ratio of short and long crystallographic axis c/a. The resulting energy landscape is used to calculate the transition probabilities between three martensite variants and the austenite state under applied stress and external magnetic field. The magnetic shape memory effect is simulated for different loading conditions and sample geometries. We demonstrate the influence of the c/a dependence of the anisotropy energy as well as the influence of twinning strain and elastic modulus on the transition between martensite variants. The model calculations are compared with experimental results on Ni-Mn-Ga single crystals.

Magnetic anisotropy in Ni–Mn–Ga martensites

We study the temperature dependence of the magnetic anisotropy of three different martensites known to exist in the Ni–Mn–Ga alloys. The anisotropy constants were determined from magnetization curves measured at different temperatures. The anisotropy of five-layered modulated tetragonal martensite is uniaxial with easy magnetization direction along short crystallographic axis. At room temperature K1(rt)=1.65×105 J m−3 and K2 is negligible. Seven-layered modulated orthorhombic martensite exhibits easy magnetization direction along the shortest crystallographic axis. K1(rt)=1.7×105 J m−3 and K2(rt)=0.9×105 J m−3 referring to hard and mid-hard magnetization axes. Nonmodulated tetragonal martensite possesses a uniaxial anisotropy with easy plane and hard magnetization direction along the long crystallographic axis with K1(rt)=−2.3×105 J m−3 and K2(rt)=0.55×105 J m−3. The temperature dependence of K1(T) of five-layered martensite follows magnetization power law with exponent n=3 suggesting a single ion origin of the magnetic anisotropy in Ni–Mn–Ga martensite.

Large magnetic-field-induced strains in Ni-Mn-Ga alloys in rotating magnetic field

A single-crystal samples of near-stoichiometric Ni 2 MnGa alloys with large magnetic field induced strain (MSM effect) at room temperature have been investigated. It was found that there is a reversible reorientation of easy magnetization direction and magnetic domain structure under applied magnetic field. By means of x-ray Laue diffraction method and difractometric analysis it was ascertained that these phenomena are connected with the growth of martensitic twin variant with the short crystallographic axis (c-axis) directed along the applied magnetic field. Furthermore, by means magneto-optical investigations we have found the correlation between martensitic microstructure and magnetic domain structure. The field-induced reorientation of martensite was able to change the dimensional lengths of the samples more than 4.5 %.

Large Magnetic-Field-Induced Strains in Ni-Mn-Ga Alloys due to Redistribution of Martensite Variants

A polycrystalline and single-crystal samples of near-stoichiometric Ni2MnGa alloys have been investigated. It was confirmed that martensite short crystallographic axis (c-axis) is the easy axis of magnetization. The reversible reorientation of the easy magnetization direction of martensite samples after 5% compression is found. The same reversible reorientation of the easy magnetization direction under applied magnetic field occurs in the single-crystal samples. The field-induced reorientation of the easy magnetization direction is accompanied with more than 4% of sample's dimension change. About the same value of the field-induced strains can be obtained for polycrystalline samples after appropriate thermo-mechanical treatment.

Crystal and molecular structures of diazapyrenes and a study of pi\cdotspi interactions.

Two diazapyrenes, 5,10-dimethyl-4,9-diazapyrene (1) and novel 2,7-dimethyl-4,9-diazapyrene (2) have been synthesized. Their crystal structures are reported here and are the first representatives of diazapyrenes. Crystal data: (1) monoclinic, P2(1)/c, a = 4.0246 (5), b = 15.5147 (5), c = 9.1453 (9) Å, beta = 101.23 (1) degrees, V = 560.1 (1) Å(3), Z = 2, R = 0.043; (2) monoclinic, C2/m, a = 12.4968 (3), b = 11.4751 (4), c = 3.9615 (5) Å, beta = 96.80 (1) degrees, V = 564.09 (5) Å(3), Z = 2, R = 0.0405. The experimental bond lengths are compared with those calculated by molecular mechanics (MM3), semi-empirical methods (MOPAC6.0-PM3, AM1, MNDO) and values predicted by valence-bond and variable-electronegativity self-consistent field (VESCF) methods. pi.pi interactions in (1), (2) and seventeen other pyrene and pyrene-like molecules selected from the Cambridge Structural Database [Allen & Kennard (1993). Chem. Des. Autom. News, 8, 131-137] have been studied. The following quantitative parameters of pi.pi interactions have been calculated: the shortest crystallographic axis, the offset parameter, the interplanar angle, the interactive volume and the overlapping surfaces. They are used for the classification of crystal-packing motifs; a high predominance of beta and a few cases of gamma and sandwich-herringbone types are observed. In addition, electronegativity, the sum of partial atomic charges of the ring non-H atoms and the number of aromatic skeleton electrons are used as parameters for classification. MOPAC-PM3 was used to calculate the partial atomic charges in (1), (2) and pyrene analogues. Correlations between geometrical and electronic structure parameters reveal an analogy between the beta-type structures and the crystal structure of graphite.

Molecular and crystal structure of 2-cyano-(2E)-pentadien-2,4-oic acid and ethyl-2-cyano-(2E)-pentadien-2,4-oate

X-ray study of 2-cyano-(2E)-pentadien-2,4-oic acid (1) and its ethyl ester (2) showed that the molecules of1 and2 in the crystalline phase form stacks by translating along the shortest crystallographic axis. The nature of the intermolecular interactions favoring the formation of such β-structures was analyzed within the framework of the Bader topological theory. Possible routes of topochemical reactions of compounds1 and2 are considered.

π-π Interactions between Pyrylium and Phenyl Rings in the Crystal

Abstract The crystal structures of two isomeric phenyl-substituted pyrylium perchlorates, 2,6-di-methyl-4-phenylpyrylium (1) and 2,4-dim ethyl-6-phenylpyrylium (2), have been determined. Both cations are planar in the crystal so that the electron deficient pyrylium rings can interact strongly with the phenyl rings of adjacent molecules forming stacks along the shortest crystallographic axis. The phenyl rings may act as donors in a charge transfer interaction which is more pronounced in 1 than in 2. Charge transfer appears as a non-mandatory consequence of the π-π stacking. The structures demonstrate the electrostatic nature of these interactions conforming to the model of Hunter and Sanders [ 1 ].

Hydrogen bond connectivity patterns and hydrophobic interactions in crystal structures of small, acyclic peptides.

Crystal structures of all available unblocked linear peptides with two to five residues were retrieved from the Cambridge Structural Database and their intermolecular contacts and packing modes studied using molecular graphics. This survey reveals that interactions between hydrophobic portions of the molecules are critically important in determining the overall features of their crystal packing patterns. Distinct hydrophobic columns or layers are observed in almost all crystal structures. Analyses of the relationships between these interactions and crystal growth properties of small peptides are given. It is suggested that needle growth is promoted by hydrophobic packing, usually along a short crystallographic axis (4.6-6.0 angstroms). Also contributing to these morphologic characteristics are entropic factors associated with hydrophobic aggregation as well as tightly bound water molecules on hydrophobic faces. The paper also provides a comprehensive overview of hydrogen bond patterns in acyclic peptide crystals. It is demonstrated that one of their primary roles is to provide a scaffolding within which hydrophobic groups can aggregate. Even though there is a high density of hydrogen bonds in the crystals, often with complex patterns and networks, certain motifs are found to recur in a number of structures indicating specific hydrogen bond preferences. Water, for example, is an integral part of the hydrogen bond networks in these crystals, usually acting as the primary donor for main-chain carboxylate groups in peptide hydrates.

Lewis-Base Adducts of Group 11 Metal(I) Compounds. XLIII. Synthesis and Structural Systematics of 1 : 1 Copper(I) Halide/Nitrogen Base Adducts as [(N-base)1(CuX)1]∞ 'Split-Stair' Polymers (X = Cl, Br, I; N-Base = Acridine, Quinaldine and 2,6-Dimethyl- and 2,4,6-Trimethyl-Pyridine)

The complete array of single strand ('split-stair') polymers for the 1 : 1 system CuX/monodentate nitrogen base, L, all X= Cl, Br, I, has now been synthesized and structurally characterized by using the highly hindered pyridine bases, L= acridine and quinaldine . Similar polymers, [ LCuX ] ∞, are also obtained with L = 2,6-dimethylpyridine for X = Cl, Br (but not I which is a dimer , [LCuI2CuL]), and for L = 2,4,6- trimethylpyridine, X = Br, I (but not Cl, which is ionic [CuL2]+[CuCl2]-). A general feature of all polymeric structures, although diverse in space group and not isomorphous in respect of polymer disposition, is the presence of a short crystallographic axis (about 4 � ) as the unit translational repeat distance.