Chiral Gay–Berne model for molecular dynamics computer simulations

Abstract

We have extended the chiral Gay–Berne (GB) pair potential of Memmer and co–workers [Liq. Cryst. (15), 345 (1993)] to the general case of biaxial ellipsoids, and we provide explicit expressions for the gradient and the torques to be used in molecular dynamics (MD) codes. To test our results against published results we have performed MD simulations of samples formed by N?=?1024 uniaxial GB ellipsoids with constant volume, and we have studied how the thermotropic behavior is affected by particle chirality. We have run temperature scans starting from isotropic samples and found clear signatures of the spontaneous formation of both lower temperature blue and cholesteric phases.     

Interferometric study of the growth kinetics of K2Co(SO4)2 · 6H2O and K2Ni(SO4)2 · 6H2O crystals

Crystallography Reports - The growth kinetics of the (001) and (110) faces of K2Co(SO4)2 · 6H2O and K2Ni(SO4)2 · 6H2O crystals in the kinetic mode has been in situ investigated for the...     

Metal-hydroxycarboxylate interactions: syntheses and structures of K2[VO2(C6H6O7)]2·4H2O and (NH4)2[VO2(C6H6O7)]2·2H2O

Potassium and ammonium dimeric (citrato)dioxovanadium(V) hydrate K₂[VO₂(H₂cit)]₂·4H₂O1 and (NH₄)₂[VO₂(H₂cit)]₂·2H₂O2 (H₄cit=citric acid) have been prepared and characterized by X-ray structure analyses. Vanadate1 crystallizes in the monoclinic space groupP2₁/n (No. 14) with unit cell parameters:a=9.304(2),b=11.756(2),c=11.911(2)Å, =111.72(3)°, andD _c=1.911 g/cm³,Z=2; Vanadate2 also crystallizes in the monoclinic space groupP2₁/n with unit cell parameters:a=9.719(2),b=11.111(3),c=11.294(2)Å, =109.03(2)°, andD _c=1.781 g/cm³,Z=2. Each dimer contains a centro-symmetric planar four-member V₂O₂ ring with two exocyclic citrate entities coordinated by the oxygen atoms of the hydroxy-and -carboxylate ligands, while the other two -carboxylate groups remain uncomplexed. Principal dimensions of the V–O bonds are 1.986(4)_av (hydroxy) and 1.980(3)Å(-carboxyl) for vanadate1, 1.988(2)_av (hydroxy) and 1.974(3)Å(-carboxyl) for vanadate2.     

Molecular dynamics simulation for the rapid solidification process of MgO–Al2O3–SiO2 glass–ceramics

A molecular dynamics simulation method was used to study the effects of the microstructure on the solidification process of different cooling rates in the MgO–Al₂O₃–SiO₂ glass–ceramics with cordierite as the main crystalline phase. The reasons for changes in the microstructure during the solidification process were analysed by the radial distribution function curve, the bond angular distribution, the coordination number and the volume changes. The results showed that the cooling rate greatly affected the crystallisation process and the glass transition process. When the cooling rate was too fast, the atoms could not undergo a massive displacement before they were “frozen”, and the ability of atoms to achieve an equilibrium position was limited. Some amorphous phases were formed as a result of the disorder of the atomic arrangement, then some crystalline phase precipitated from the vitreous, and a glass–ceramic material was eventually formed.     

Structure of progesterone hydroquinone monohydrate (1∶1∶1), C21H30O2·C6H6O2·H2O

The crystal structure of progesterone hydroquinone monohydrate was determined by means of X-ray diffraction methods:M _r=442.6, orthorhombic,P2₁2₁2₁,a=14.680(2),b=22.725(3),c=7.334(1) Å,V _a=2446.6(6) ų,Z=4,D _x=1.190 M gm^–3, MoK radiation ,(MoK)=0.75 cm^–1,F(000)=948. The structure was solved usingMultan;R=0.059,R _w=0.059 for 2736 reflections. This progesterone molecule has the most flattenedA ring, relative to the rest of the skeleton, of all progesterone molecules studied so far. Steroid, hydroquinone, and water molecules form, by means of hydrogen bonds, two parallel chains connected with each other by hydrogen bonds.The authors thank Dr. A. Szyczewski for supplying crystals. This research was supported by the project RP.II.10 from the Polish Ministry of National Education and by PHS Grant No. DK26546.     

Peculiarities of the micromorphology of the CaC2O4 · H2O crystal faces

Crystallography Reports - Peculiarities of the faceted microrelief formed during the growth of CaC2O4 · H2O calcium oxalate monohydrate (whewellite) crystals are investigated to gain insight...     

Crystal and molecular structure of 7-hydroxyflavone monohydrate, C14H10O3·H2O

The X-ray crystal structure of 7-hydroxyflavone monohydrate, C₁₄H₁₀O₃ · H₂O, is determined. The compound crystallizes in the monoclinic space group, P2₁/n with a = 3.801(3), b = 19.665(4), c = 16. 039(6), = 93.69(3)°, and = 0.68 mm^–1 for Z = 4. The phenyl ring of the flavone moiety is rotated 18.6(1)° out of the penzopyran plane, which is a typical value for flavones. In the crystal lattice, there are wide channels which are lined mainly by C–H groups. The water molecules enclosed in these channels are severely disordered.     

Synthesis and crystal structure of [Cu(azpy)(H2O)4][Cu2(nta)2(azpy)]····6H2O: A two-dimensional network solid

The copper(II) complex [Cu(azpy)(H₂O)₄][Cu₂(nta)₂(azpy)]····6H₂O (nta = nitrilotriacetate, azpy = 4,4-azobispyridine) has been synthesized and structurally characterized. It crystallizes in the triclinic space group P , a = 8.6985(3) Å, b = 9.4776(3) Å, c = 14.6544(5) Å, = 71.5360(10)°, = 85.7600(10)°, = 88.1420(10)°, V = 1142.74(7) ų, Z = 1. The crystal structure consists of one-dimensional linear chain cations and dimeric anions. The copper centers in the anion possess distorted trigonal bipyramidal geometry, while Cu(2) has a distorted octahedral geometry in the cation. Coordinated water molecules in the one-dimensional chain form interionic hydrogen bonds with the oxygen atoms of the carboxylate of nta of the dimmer anion. These hydrogen bonds result in the formation of a two-dimensional network.     

Silicogermanate Ba2K2In2[(Si0.8Ge0.2)6O18] · 2H2O As an Analogue of the Natural Zirconosilicate Kostylevite K4Zr2[Si6O18] · 2H2O

Crystallography Reports - Crystals of new silicogermanate Ba2K2In2[(Si0.8Ge0.2)6O18] · 2H2O were prepared by the hydrothermal synthesis; sp. gr. P21/n, a = 6.5548(6) Å, b = 11.6946(10)...     

On the Crystal Structures of the Polymorphs of Manganese(II) Chloride Tetrahydrate: α-MnCl2·4H2O and β-MnCl2·4H2O

Journal of Chemical Crystallography - The manganese(II) chloride tetrahydrate MnCl2·4H2O (α-form) crystallizes in the space group P21/n with a?=?6.1918(4) Å,...     

Complexation between tungsten(VI) and citrate: The crystal and molecular structure of a dinuclear complex,Na6[W2O5(cit)2]·10H2O

The crystals of the title compound are monoclinic, space groupP2₁/c witha=9.014(1),b=9.8668(5)c=17.5000(3) Å,=91.50(1)°,V=1556(1) ų. The structure was determined by Patterson methods and refined by least squares toR=0.038 for 3829 observed reflections and 224 parameters. There are two tungsten dimers in the unit cell, each formed by a bridging oxygen lying on a center of symmetry. Each tungsten has five more coordination sites; two occupied by terminal oxygens and the remaining three by citrate oxygens. Waters of crystallization are distributed throughout the cell and together with various of the anion oxygens, make the sodium cations either five-or six-coordinate.     

Structural and spectroscopic characterization of the macrocyclic complex: [Tb(CrO4)(H2O)(C22H26N6)] ·0.5(Cr2O7)·(H2O)

The title complex was obtained by anion metathesis from [Tb(CH₃COO)₂(C₂₂H₂₆N₆)] (CH₃COO)·4H₂O and K₂CrO₄ in aqueous solution. The compound crystallizes in the triclinic space group witha=8.384(2),b=10.425(2)c=15.752(2)Å, =98.82(2), =93.52(2), =97.22(2)°, andZ=2. The structure is ionic and consists of a (+1) complex cation balanced in a 21 ratio by a disordered dichromate ion. The 9-coordinate Tb(III) is linked to the six nitrogen atoms of the macrocyclic ligand L=C₂₂H₂₆N₆, as well as to a water molecule and a bidentate chelating chromate situated on opposite sides of the macrocycle. The infrared spectrum shows, in addition to the pattern of the macrocyclic ligand, the absorptions arising from the stretching modes of the bidentate chelating CrO₄ ^2– ligand and of the Cr₂O₇ ^2– counterion.     

Crystal structure of aminoguanidinium hexahydro-closo-hexaborate dihydrate, (CN4H7)2B6H6 · 2H2O

The (HAgu)₂B₆H₆ · 2H₂O compound was synthesized and its crystal structure was determined [R = 0.0385 for 2018 reflections with I > 2σ(I)]. The structure consists of HAgu ⁺ cations, centrosymmetric B₆H ₆ ^2? anions, and water molecules. The anions have an almost regular octahedral structure. The bond lengths and angles lie within the following narrow ranges: B-B, 1.715–1.726(2) Å; B-H, 1.08–1.14(2) Å; B-B-B, 59.72°–60.29(9)° and 89.63°–90.20(11)°; and B-B-H, 133.2°–137.0(9)°. The HAgu ⁺ cations and water molecules are involved in the O-H?O, N-H?O, and N-N?N hydrogen bonds and participate in numerous (N, O)-H?H-B specific interactions with the B₆H ₆ ^2? anions, which results in splitting and high-frequency shift of the band of B-H stretching vibrations in the IR spectrum.     

A dinuclear cyanide-bridged complex, [(DMF)4(H2O)3LuCo(CN)6]·H2O

The crystal structure of the bimetallic cyanide bridged complex [(DMF)₄(H₂O)₃LuCo(CN)₆]·H₂O (1) was obtained by single-crystal X-ray diffraction. The central lutetium(III) ion is eight coordinate arranged in a square antiprism while the cobalt(III) ion is six coordinate, oriented octahedrally. Molecules in the crystal lattice are held together by a network of hydrogen bonding. Crystallization of 1 occurs in the centrosymmetric monoclinic space group P2₁/c (No. 14) with a = 13.875(2), b = 8.8352(9), c = 24.633(2) Å = 96.392(8)° and Z = 4.     

Synthesis and crystal structure of [Ni(H2O)6](C19H17O9S)2·2H2O

A water soluble flavonoid sulfate, [Ni(H₂O)₆](C₁₉H₁₇O₉S)₂·2H₂O was synthesized and its structure was determined by single-crystal X-ray diffraction analysis. The crystal of it belongs to triclinic crystal system, space group P–1. The results show that the title compound consists of [Ni(H₂O)₆]²⁺, C₁₉H₁₇O₆SO₃ ⁻ and H₂O. Ni(II) is located on the symmetry center and octahedrally coordinated by six water molecules. A variety of hydrogen bonds among [Ni(H₂O)₆]²⁺, C₁₉H₁₇O₆SO₃ ⁻ and the lattice water molecules build a hydrophilic region. Aromatic π–π stacking interactions assemble isoflavone skeletons into a column and the columns form a hydrophobic region of the title compound. The sulfo-groups bridge the hydrophilic regions and the hydrophobic regions as well as the inorganic components and organic components. Hydrogen bonds, stacking interactions and the electrostatic interactions between cation [Ni(H₂O)₆]²⁺ and anion sulfonate C₁₉H₁₇O₆SO₃ ⁻ lead the moieties to a three-dimensional structure.     

α-NiSO4·6H2O晶体生长与光学性质

用水溶液降温法生长出光学品级的α-NiSO4·6H2O大单晶,对晶体的透过光谱和(001)晶面的X射线衍射性能进行了测试和表征.     

Crystal structures of acid ethylenediaminetetraacetates [Cd(H2 Edta)(H2O)] · 2H2O and [Mn(H2O)4][Mn(HEdta)(H2O)]2 · 4H2O

The crystal structures of [Cd(H₂ Edta)(H₂O)] · 2H₂O (I) and [Mn(H₂O)₄][Mn(HEdta)(H₂O)]₂ · 4H₂O (II) are studied by X-ray diffraction [R ₁ = 0.0209 (0.0272), wR ₂ = 0.0571 (0.0730) for 2551 (4025) reflections with I > 2σ(I) in I (II), respectively]. Structure I contains mononuclear [Cd(H₂ Edta)(H₂O)] complexes with the C ₂ symmetry, and structure II contains centrosymmetric trinuclear [Mn(H₂O)₄][Mn(HEdta)(H₂O)]₂ complexes. In I and II, the protonated ligands are hexadentate (2N + 4O), and the water molecule increases the coordination number of the metal atom to seven. The acid protons participate in short intermolecular hydrogen bonds, which are symmetric in II and asymmetric in I.     

配合物[Cu2(C6H2Cl2OC=N-C3H6COO)2(H2O)2]·3H2O合成与晶体结构

本文以苏氨酸,3,5-二溴水杨醛以及醋酸铜为原料合成了新型配合物[Cu2(C6H2Cl2OC=N-C3H6COO)2(H2O)2]·3H2O,并对其晶体结构经元素分析,红外光谱及X射线单晶衍射表征.结果表明:该晶体属单斜晶体结构,晶胞参数分别为:a=0.6985(2) nm, b=1.0789(2) nm, c=1.9639(3) nm, β=92.182(3) °, Mr=797.34, V=1.4789(6) nm3 , Z=2, Dc=1.790 g/cm3, μ(MoKa) =1.867 mm-1, F(000)=808, R=0.0321, wR= 0.0566.Cu(II)与一个N原子,两个O原子以及一个水分子构成三齿链状席夫碱.不对称单元结构包含两个配合物分子及三个由氢键链接的水分子.     

[Co(H2O)6](C18H15O4SO3)2·4H2O的合成和晶体结构

以芒柄花素为先导化合物,合成了水溶性的[Co(H2O)6](C18H15O4SO3)2·4H2O,并采用IR, 1H NMR, TG-DTA, XRD和单晶X射线衍射法对其结构进行了表征.单晶X射线衍射结果表明:[Co(H2O)6]2+、C18H15O4SO 3和H2O之间存在多种氢键,形成晶体结构中的亲水区.异黄酮骨架间反平行排列,面对面和边对面芳香堆积作用同时存在于其中,构成晶体结构中的疏水区.磺酸根是连接亲水区和疏水区的桥梁.氢键、芳香堆积作用以及阴阳离子之间的静电引力共同将标题化合物组装成具有三维网络结构的超分子.