Low-Temperature Crystal Structure of S-camphor Solved from Powder Synchrotron X-ray Diffraction Data by Simulated Annealing

The ordered, low-temperature crystal structure of the pure enantiomer of camphor (C₁₀H₁₆O) has been solved from high-resolution powder synchrotron X-ray diffraction data. The structure is orthorhombic, space group P2₁2₁2₁, Z=8, with a=8.9277(2) Å, b=27.0359(5) Å, and c=7.3814(1) Å at 100 K. The structure was solved by autoindexing of the pattern, space group determination, and then optimization of the positions and orientations of the two independent molecules in the unit cell by simulated annealing. The molecular structure obtained from the restrained Rietveld refinement shows reasonable agreement with that optimized from ab initio molecular orbital calculations. In the crystal structure, the molecules are aligned antiferroelectrically and weak C-H…O hydrogen bonds link together the independent molecules.     

A reversible solid–solid phase transition Z′ = 1 to Z′ = 6 in [Ni(OAc)(PNP)]OTf

At ambient temperature, the complex [Ni(OAc)(PNP^tBu)]OTf has one independent molecule in the asymmetric unit of the crystal structure with very large anisotropic displacement parameters. During cooling a fully reversible solid–solid phase transition occurs at a discrete temperature in the range 210–230 K. The low-temperature phase has six independent, well ordered molecules in the asymmetric unit. The P2₁/a space group symmetry of the high-temperature phase changes to P2₁/n for the low-temperature phase and the c-axis increases by a factor of six. The acetate ligand is shown to be coordinated in a η¹-fashion through one of the oxygen atoms, with the sterically encumbered, tridentate PNP^tBu ligand completing the square planar geometry around the Ni^II ion. The synthesis and full characterization of the complex is reported.     

X-Ray Diffraction Study of 2-Aminopropenenitrile at 97 K

2-Aminopropenenitrile crystallizes in the space group P2₁2₁2₁ with two molecules in the asymmetric unit. Both molecules show appreciable pyramidalization at the amino group. The crystal structure is built from approximately centrosymmetric dimers stabilized by hydrogen bonding between the amino group of each molecule and the nitrile group of its partner. The dimers are linked into chains by further hydrogen bonds in which the amino group of one molecule acts as donor, the amino group of the other as acceptor. The two types of molecule thus play different roles in the crystal structure. Electron density difference maps for the two independent molecules show characteristic bonding density features. The molecular structure as obtained by the low-temperature X-ray analysis is closely similar to that derived from ab initio molecular orbital calculations and leads to rotational constants close to those obtained from a microwave spectroscopic study.     

Crystal and molecular structure of the copper(II) Schiff-base complex containing the azo group

From 3-allyl salicylaldehyde and 4-aminoazobenzene (HL), the Schiff-base complex of copper(II) is synthesized and structurally characterized. The crystallographic unit of a CuL₂ (1) single crystal contains two independent molecules of the complex. Coordination polyhedra of copper atoms are slightly distorted squares; azomethine ligands are in the trans-position. The neighboring molecules of the complex are bonded by intermolecular π stacking interactions.     

[MPy4(NCO)2]-2Py clathrates (M = M(II) = Mn,Fe, Co,Ni, Cu,Zn, Cd; Py = pyridine)

The title compounds form an iso structural series and are isomorphic with other [MPy₄X₂]-2Py clathrates (XRD, KM4 diffractometer, cell parameters and space group Ccca from 17–80 reflections). In the clathrate [NiPy₄(NCO)₂]-2Py studied in detail (XRD, CAD-4 diffractom eter, λCuK_α, Ω/2θ scan mode, θ_max = 78‡, 990 strong reflections, 104 parameters, R = 0.053), the host molecule has 222 symmetry, and the twofold axes run along the coordination bonds. The transoctahedral environment of nickel consists of six nitrogen atoms of four pyridine and two isocyanate ligands. The coordination polyhedron is slightly distorted due to changes in the bond lengths. The molecule has a propeller conformation. The guest molecules lie in the cavities of the crystal structure in conformity with the van der Waals type of packing. The host complex [NiPy₄(NCO)₂] (XRD, CAD-4 diffractometer, 4615 strong reflections, 560 parameters, R-0.037) crystallizes in the triclinic crystal system (space group P1) with two independent asymmetric molecules in the unit cell. The molecular structure is analogous to that in the ciathrate phase, but the coordination angles are severely distorted; one of the molecules acquires a distorted propeller conformation, and the other, a centrosvmmetric conformation, which is less favorable. While being structurally identical, the [MPy₄(NCO)₂]-2Py clathrates differ heavily in the properties. The first four complexes dissociate to host complexes, and their thermal stability changes in the sequence Mn< Fe< Co< Ni; the Cu and Zn clathrates decompose in one step to dipyridine complexes with decomposition of host complexes. Decomposition of the Cd ciathrate follows one of these patterns depending on conditions. The results are compared with those for other known systems. Synthetic procedures are given. Translated fromZhurnal Strukturnoi Khimii, Vol. 40, No. 5, pp. 935–953, September–October, 1999.     

Heat capacity of α-glycylglycine in a temperature range of 6 to 440 K

Heat capacity of α-glycylglycine was measured using adiabatic calorimetry (6 to 304 K) and DSC (264 to 443 K), and then thermodynamic functions were calculated. Heat capacity has no anomalies. The molecular crystal melts at 493 K (enthalpy of melting is about 62 kJ mol^–1). The melting is accompanied by decomposition. C _P(T) function for glycylglycine is very similar to those of three glycine polymorphs. The ‘universal’ curve consists of two parts: low-temperature Debye-like function (from 0 to about 120 K) and a straight line (up to the melting point). At very low temperatures rigid molecules oscillate as a whole, and the Debye temperature is proportional to the molecular mass to the power of 3/2.     

Synthesis and crystal structure of aquabis(isothiocyanato)(18-crown-6)lead(II)(isothiocyanato)-(18-crown-6)(nitrato-<Emphasis Type="Italic">O,O</Emphasis>′)lead(II)

A new mixed complex compound, aquabis(isothiocyanato)(18-crown-6)lead(II)(isothiocyanato)-(18-crown-6)(nitrato-O,O′)lead(II) [Pb(NCS)₂(18-crown-6)(H₂O)][Pb(NCS)(NO₃)(18-crown-6)] is prepared, and its crystal structure is studied by XRD analysis. The structure was solved by the direct method and was refined by full-matrix least-squares method in anisotropic approximation to R = 0.044 for all 3648 measured independent reflexes (automatic diffractometr CAD-4, λMoK _α). This crystal structure contains two symmetrically independent halves of the two individual and differing in type complex “guest-host” molecules. One of them (with the H₂O ligand molecule) is located on the crystallographic axis 2, and the other is located around the crystallographic inversion center and is statistically disordered relative to this center (except for its crown-ligand).     

Molecular Structure of 1-Germatrahol and its Complex With Chloroform

The crystal structures of anhydrous 1-germatranol and its complex with HCCl₃ are centrosymmetrical dimers because of their intermolecular hydrogen bonds. In the germatranol crystal, the axial and equatorial oxygen atoms of its two molecules are hydrogen bonded into an eight-membered coordination cycle. In the complex with HCCl₃, the two molecules of germatranol are likewise linked in dimers, and both axial oxygen atoms are H bonded with HCCl₃. In the investigated structures, the axial Ge—O bond is shorter than the equatorial ones. Depending on the number and strength of the hydrogen bonds, the interatomic Ge—O and Ge ← N distances change markedly. The quantitative estimates of the H bond energy are obtained from quantum chemical calculations of the model systems containing 1-germatranol and HCCl₃ molecules.     

1，4-二氮杂二环[2.2.2]辛烷-氰基合钴(Ⅲ)三维框架氢键型晶体的合成、相变及介电性质

室温下以1,4-二氮杂二环[2.2.2]辛烷（Dabco）和钴氰酸为原料、水和甲醇为混合溶剂,以缓慢蒸发的方式获得Dabco-氰基合钴氢键型框架晶体材料（H₃O）（H₂Dabco）[Co （CN）₆]·H₂O （1）。并通过单晶X射线衍射、红外光谱、元素分析、粉末X射线衍射、热重分析、差示扫描量热、变温-变频介电常数测试对其结构、热性能与电性能进行表征。在低温（100 K）与室温（296 K）下,化合物均为单斜晶系P2₁/c空间群。单晶结构显示氰基合钴阴离子、水分子与水合质子在晶体内部通过氢键的相互作用形成三维网状框架,质子化的（H₂Dabco）²⁺阳离子镶嵌在其中构成分子马达型囊状结构。随着温度的升高（H₂Dabco）²⁺阳离子发生弹簧式扭转,从而引发晶体在254 K附近相变,在相同温度下沿着晶体的3个轴向发生介电异常,呈现明显的介电各向异性。     

Synthesis and X-ray diffraction study of complex oxides of the Zn2 ? x(ZraSnb)1 ? xFe2xO4 composition

A multicomponent system of complex refractory oxides of the composition Zn_{2 − x} (Zr _a Sn _b )_{1 − x} Fe_2x O₄ (a + b = 1; a: b = 1: 5, 1: 4, 1: 3, 1: 2, 1: 1, 2: 1, 3: 1, 4: 1; x = 0−1.0; Δx = 0.05) was studied by X-ray diffraction. The samples were prepared from oxides of appropriate metals by low-temperature plasma synthesis (hydrogen-oxygen flame). Two phases with wide homogeneity ranges were identified: α phase crystallized in the crystal system of inverse cubic spinel and β phase with the structure of tetragonal spinel. The phase boundaries were found. Structural data are presented for about 100 solid solutions.     

Crystal structure and mesogenic behaviour of a new fluorene derivative: 9,9‐dimethyl‐2,7‐bis(4‐pentylphenyl)‐9H‐fluorene

The title compound, C₃₇H₄₂, is a new mesogenic compound containing the fluorene moiety. It exhibits enantiotropic nematic liquid crystalline behaviour with melting at 125 °C and isotropization at 175 °C. The crystallographically independent unit contains two molecules oriented face‐to‐edge with respect to each other. The two molecules have nearly the same conformation of the bis‐phenyl fluorene moiety. The molecular packing in the crystal phase is nematic‐like.     

Synthesis, characterization, and single crystal X-ray structures of [CoIII((BA)2en)(thiobenzamide)2]PF6 and [CoIII(acacen)(thiobenzamide)2]ClO4 and their solvatochromic properties

New cobalt(III) complexes of two tetradentate Schiff base ligands, acacen = bis(acetylacetone)ethylenediimine dianion and (BA)₂en = bis(benzoylacetone)-ethylenediimine dianion, with two axial thiobenzamide (tb) ligands have been synthesized by solid state methods and characterized by elemental analyses, IR, UV–Vis, and ¹H-NMR spectroscopy. Both complexes show solvatochromism in a variety of solvents. The crystal and molecular structures of (1) and (2) were determined by X-ray crystallography. The structure (1) contains two independent [Co^III((BA)₂en)(tb)₂]⁺ complexes, two independent PF₆ anions, and one well ordered ethyl acetate solvent molecule per asymmetric unit. In contrast, the structure (2) contains two independent [Co^III(acacen)(tb)₂]⁺ complexes of C₂ symmetry, a disordered ClO₄ group and disordered toluene molecules. The octahedral coordination of Co(III) is distorted and the Schiff base ligands (ONNO donors) coordinate the cobalt ion in four equatorial positions, and the two axial positions are occupied by S-bonded thiobenzamide molecules. Intramolecular N–H···O hydrogen bonds donated by the thiobenzamide molecules add to the stability of the complexes in the solid state. The IR, UV–Vis, and ¹H-NMR spectra of the two complexes and their solvatochromic properties are also discussed. The compounds exhibit LLCT mediated by the metal center. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Crystal structure of 1,9-dimethyl-4,5-dihydro-6H-pyrido[3’,2’:4,5]thieno[2,3-f] pyrrolo[1,2-a][1,4]diazepin-6-one

A new tetracyclic compound, 1,9-dimethyl-4,5-dihydro-6H-pyrido[3’,2’:4,5]thieno[2,3-f]pyrrolo[l,2-a][1,4]diazepin-6-one (2) was isolated and studied by X-ray crystallography. Compound 2 crystallizes in the orthorhombic system, space group Pna2₁, a = 11.1098(8) ?, b = 8.4815(6) ?, c = 28.367(2) ?, V= 2673.0(3) ?³, Z=8. The crystal structure comprises two crystallographically independent molecules of the compound. They relate as stereoisomers; in each the diazepine ring exhibits a boat conformation. The crystal packing reveals zigzag H-bonded chains with two distinct hydrogen bonds. The H…O distances and N-H…O angles for N3-H3…O1’ are 2.012? and 174°, and for N3’-H3’…O1 are 1.974? and 154°, respectively.     

Underpotential surface reduction of mesoporous CeO<Subscript>2</Subscript> nanoparticle films

The formation of variable-thickness CeO₂ nanoparticle mesoporous films from a colloidal nanoparticle solution (approximately 1–3-nm-diameter CeO₂) is demonstrated using a layer-by-layer deposition process with small organic binder molecules such as cyclohexanehexacarboxylate and phytate. Film growth is characterised by scanning and transmission electron microscopies, X-ray scattering and quartz crystal microbalance techniques. The surface electrochemistry of CeO₂ films before and after calcination at 500 °C in air is investigated. A well-defined Ce(IV/III) redox process confined to the oxide surface is observed. Beyond a threshold potential, a new phosphate phase, presumably CePO₄, is formed during electrochemical reduction of CeO₂ in aqueous phosphate buffer solution. The voltammetric signal is sensitive to (1) thermal pre-treatment, (2) film thickness, (3) phosphate concentration and (4) pH. The reversible ‘underpotential reduction’ of CeO₂ is demonstrated at potentials positive of the threshold. A transition occurs from the reversible ‘underpotential region’ in which no phosphate phase is formed to the irreversible ‘overpotential region’ in which the formation of the cerium(III) phosphate phase is observed. The experimental results are rationalised based on surface reactivity and nucleation effects.     

Supramolecular Ribbons. Crystal Structure and Spectroscopic Properties of 2,2′-Bipyrroyl

 A crystal structure determination of 2,2′-bipyrroyl (1; 2,2′-dipyrryl-diketone, bis (2-pyrrolyl)ethanedione) and its spectroscopic properties in solution are reported. In the crystal, 1 self-assembles via hydrogen bonding into supramolecular ribbons that extend indefinitely through the crystal lattice. The observed molecular conformation is one where each pyrrole ring and adjacent carbonyl group are co-planar (torsion angle ∼ 0.9°), with the N-H pointing in the same direction as the C=O. The two carbonyls have a transoid but not co-planar geometry with a torsion angle of ∼128°. Adjacent molecules in the crystal are linked by pairs of intermolecular hydrogen bonds, pyrrole NH to carbonyl oxygen, to form a matrix of polymeric chains that lie like neatly stacked, parallel streams of ribbons. Molecular mechanics calculations on the monomer indicate an intra-molecularly hydrogen bonded planar conformation (sp, ap, sp) at the global energy minimum. In CHCl₃, 1 is monomeric according to vapor pressure osmometry (MW _obs=179±10 vsċMW _calc=188). In THF, the measured molecular weight is 340±15, which corresponds best to one molecule of 1 solvated by two THF molecules (MW=322 for C₁₀H₈N₂O₄ċ2 C₄H₈O) rather than to a dimer.     

Supramolecular Ribbons. Crystal Structure and Spectroscopic Properties of 2,2′-Bipyrroyl

Summary.  A crystal structure determination of 2,2′-bipyrroyl (1; 2,2′-dipyrryl-diketone, bis (2-pyrrolyl)ethanedione) and its spectroscopic properties in solution are reported. In the crystal, 1 self-assembles via hydrogen bonding into supramolecular ribbons that extend indefinitely through the crystal lattice. The observed molecular conformation is one where each pyrrole ring and adjacent carbonyl group are co-planar (torsion angle ∼ 0.9°), with the N-H pointing in the same direction as the C=O. The two carbonyls have a transoid but not co-planar geometry with a torsion angle of ∼128°. Adjacent molecules in the crystal are linked by pairs of intermolecular hydrogen bonds, pyrrole NH to carbonyl oxygen, to form a matrix of polymeric chains that lie like neatly stacked, parallel streams of ribbons. Molecular mechanics calculations on the monomer indicate an intra-molecularly hydrogen bonded planar conformation (sp, ap, sp) at the global energy minimum. In CHCl₃, 1 is monomeric according to vapor pressure osmometry (MW _obs=179±10 vsċMW _calc=188). In THF, the measured molecular weight is 340±15, which corresponds best to one molecule of 1 solvated by two THF molecules (MW=322 for C₁₀H₈N₂O₄ċ2 C₄H₈O) rather than to a dimer. Received October 21, 1999. Accepted November 2, 1999     

Zinc(II) complex of the edta bis(tyrosine) chelating agent

The synthesis and results of X-ray structural analysis for a novel zinc(II) compound, Zn(O₁₂N₄C₂₈H₃₂)·₆H₂O, are reported. The compound is triclinic, P1, with unit cell parameters a = 11.0906(3) Å, b = 13.1404(3) Å, c = 14.0725(3) Å; β = 89.910(1)°. In contrast to the analogous Cu(II) complex, the unit cell contains two independent molecules of the Zn(II) complex and twelve independent molecules of water. The text was submitted by the authors in English. Zhurnal Strukturnoi Khimii, Vol. 48, No. 4, pp. 760–763, July–August, 2007.     

Synthesis and study of organic nitrates of the heterofunctional series 3. Synthesis and structure of tris(hydroxymethyl)aminomethane dinitrate benzoate hydronitrate

Tris(hydroxymethyl)aminomethane dinitrate benzoate hydronitrate, the first representative of mixed nitric and carboxylic esters of aminopolyatomic alcohols, was obtained by the reaction of a mixture of concentrated HNO₃ and Ac₂O with 4,4-bis(hydroxymethyl)-2-phenyl-2-oxazoline. X-ray structural analysis demonstrated that the title compound exists in the crystal as two independent molecules. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 505–509, March, 1999.     

Crystal structure and quantum chemical investigation of [Cd(NTO)<Subscript>4</Subscript>Cd(H<Subscript>2</Subscript>O)<Subscript>6</Subscript>] · 4H<Subscript>2</Subscript>O

[Cd(NTO)₄Cd(H₂O)₆] •4H₂O was synthesized by mixing the aqueous solution of 3-nitro-1, 2,4-triazol-5-one (NTO) and cadmium carbonate. The single crystal structure was determined by a four-circle X-ray diffractometer. The crystal is monoclinic, space group C2/c with crystal parameters of a = 2.1229(3) nm, b = 0.6261(8) nm, = 2.1165(3) nm, β= 90.602 (3)°, V= 2.977(6) nm₃, Z = 4, D_c = 2.055 g • cm_-3, μ = 15.45 cm_-1 and F(000) = 1824. 2523 observable independent reflections with F₀4σ(F₀) were used for the determination and refinement of the crystal structure. Lorentz-polarization and absorption correction were applied. The final R is 0.0282 and wR = 0.0792. The analytical results show that the Cd⁺² has two kinds of coordinate bonds in one crystal. One Cd⁺² coordinates with 4 NTO anions and another coordinates with 6 water molecules to form a binucleate complex with a structure of tetrahedron and tetragonal bipyramid, respectively. By using SCF-PM3-MO method, the electron structure of cadmium complex of NTO has been calculated. The analysis of the calculated results shows that when [Cd(NTO)₄Cd(H₂O)₆] • 4H₂O is heated, the crystallization waters will be dissociated first and the ligand waters second and NO₂ group has priority of leaving when NTO⁻ is decomposed. Analysis of the energy level and composition of localized molecular orbitals indicates that both the two Cd²⁺ bond to the coordinating atom with 5s     

Observation of the verwey transition in Fe3O4 by high-resolution electron microscopy

High resolution electron microscopy (HREM) of Fe₃O₄ has been carried out at temperatures near the Verwey transition (∼120 K) with a point resolution of 3 Å. Lattice fringes of both the high- and the low-temperature phases have been observed at these temperatures. The crystal symmetry of the low-temperature phase indicated by the lattice images is consistent with the result obtained by earlier diffraction studies. A series of lattice images showing the transition from the low-temperature phase (to the high-temperature phase) has been obtained. The transformation to the high-temperature phase occurs through the penetration of the high-temperature phase into areas of the low-temperature phase. A quick motion of domain boundaries in the low-temperature phase, which is consistent with almost instantaneous rearrangements of charge ordering, has been observed. The possibility of determining the ordered arrangement of Fe²⁺ and Fe³⁺ ions directly by HREM is discussed.