Hexakis(urea‐κO)zinc(II) dinitrate at 110 and 250 K: uniaxial negative thermal expansion

The crystal structure of the title compound, [Zn{CO(NH₂)₂}₆](NO₃)₂, has been determined at 110 and 250 K. The structure is stabilized by 12 individual hydrogen bonds, both intra‐ and intermolecular. Analysis of the thermal expansion tensor, based on unit cells determined over a temperature range of 180 K, shows uniaxial compression in the direction of the b axis during warming. The hydrogen bonds form layers perpendicular to this axis and these layers are connected by coordinative bonds parallel to the axis. As expected, the intermolecular hydrogen bonds expand during warming. Surprisingly, the coordinative bonds contract, accompanied by changes in the O—Zn—O angles. Overall, this behaviour can be described as an accordion‐like effect.     

Swertisin dihydrate

The title compound, 6‐C‐gluco­pyran­osyl‐7‐O‐methyl­apigenin dihydrate, C₂₂H₂₂O₁₀·2H₂O, is a natural C‐glu­cosyl­flavone. The flavone skeleton is almost planar, the dihedral angle between the pyran moiety and the 4‐hydroxy­phenyl ring being 9.8 (3)°. The basal plane of the pyran­osyl ring of the glucose moiety is almost perpendicular to the benzo­pyran ring system. The flavone skeletons are stacked along the a axis, forming layers parallel to (001). Between these hydro­phobic layers, the glucose groups and water mol­ecules of crystallization are connected via O—H⋯O hydrogen bonds, forming hydro­philic layers.     

Crystal Structure of Melaminium Orthophosphate from High‐Resolution Synchrotron Powder‐Diffraction Data

The crystal structure of melaminium orthophosphate (MP) has been determined from high‐resolution synchrotron powder‐diffraction data. The crystal packing consists of melaminium layers and pairs of orthophosphate chains connected by H‐bonds almost perpendicular to the layers. The distance between melaminium layers is 3.62 Å. Neighboring melaminium molecules do not lie in the same plane, but in two parallel planes at close distance (0.79 Å), and are shifted with respect to each other. The orthophosphate chains are connected by both intra‐chain and inter‐chain H‐bonds. The melamine is singly protonated at an endocyclic N‐atom. The powder‐diffraction data were corroborated by solid‐state NMR experiments.     

Crystal structure and tautomerism in 4-phenylisoxazoles with two potential hydroxyl groups at positions 3 and 5

The crystal structure of 4-phenyl-3-hydroxyisoxazol-5-one semihydrate exhibits an exceptional hydrogen bonded polymeric structure with a unit cell of 8 molecules. The hydrogen bonds stretch out, using the oxohydroxy groups in positions 3 and 5 in the direction of one axis and along a perpendicular direction the layers are stitched together by water molecules. The layers are stitched by using four hydrogen bridges of water molecules, the heterocyclic ring nitrogen as well as the oxygen at position 5. Tautomerism of this moiety in solution is discussed, in light of some new dialkylation products. The state in which these products exist in solution depends on the solvent. A zwitterionic tautomer is present in ether. In some alkylation conditions, the predominant dialkylation product is the N,N-disubstituted betaine (Anhydro-2,2-dialkyl-3(5)-oxo-5(3)hydroxy-4-phenylisoxazolonium hydroxide). Study of tautomerism in polar and protic solvent is unreliable owing to associations and dissociation phenomena.     

Architecture of the hydrophobic and hydrophilic layers as found from crystal structure analysis of N-benzyl-N,N-dimethylalkylammonium bromides

The molecular and crystal structures of N-benzyl-N,N-dimethylalkylammonium bromides monohydrates with chain length n=8-10 have been determined. The crystals are isostructural with the N-benzyl-N,N-dimethyldodecylammonium bromide monohydrate. The structures consist of alternated hydrophobic and hydrophilic layers perpendicular to [001]. The attraction between N+ of the cation head-groups and Br- anions is achieved through weak C_H...Br interactions. The water molecules incorporated into ionic layers are donors for two O_H...Br hydrogen bonds and serve as the acceptors in two weak interactions of C_H...O type. The methylene chains, with the slightly curved general shape, have the extended all-trans conformation. The mutual packing of the chains in the hydrophobic layers is governed by weak C_H...pi interactions.     

Structural origin of chirality and properties of a remarkable helically pillared solid

A new helically pillared and chiral solid, Cu(pzc)2AgReO4 (I, pzc = pyrazinecarboxylate), was synthesized from hydrothermal reactions at 95-125 degrees C. The structural origin of its chirality, relative to the achiral M(pzc)2(H2O)2AgReO4 (II, M = Co; III, M = Ni) analogues, arises from significantly tilted pillars and hydrogen bonds to the AgReO4 layers. The new pillared structure exhibits second harmonic generation activity, CO2 absorption, thermal stability to approximately 250 degrees C, and Curie-Weiss magnetism expected for isolated Cu2+.     

2,4‐Bis[1‐(4‐hydroxyphenyl)‐1‐methylethyl]phenol: a three‐dimensional framework built from O—H...O hydrogen bonds

In the crystal structure of the title compound, C₂₄H₂₆O₃, (I), there are three different O—H...O hydrogen bonds, which individually form chains of C(10), C(12) and C(16) types. The combined effect of all these hydrogen bonds is the formation of a three‐dimensional network, which is additionally stabilized by a single intermolecular C—H...π interaction. The significance of this study lies in the comparison drawn between the molecular structure of (I) and those of several of its analogues, which shows a close similarity in the almost perpendicular orientation of the benzene rings.     

The Crystal Structures of Pyrazine-2,6-Dicarboxylic Acid DihydRAte and Hexaaquamagnesium(II) Pyrazine-2,6-Dicarboxylate

The crystals of the pyrazine-2,6-dicarboxylic acid dihydrate [C 4 H 2 N 2 (COOH) 2 ]·2H 2 O or H 2 (2,6-PZDC)] crystallize in the monoclinic system, space group C2/m. Their structure is composed of planar layers in which the acid and the water molecules interact via a network of hydrogen bonds. The layers are also hydrogen bonded. Hexaaquamagnesium(II) pyrazine-2,6-dicarboxylate [Mg(H 2 O) 6 ] 2+ [C 4 H 2 N 2 (COO) 2 ] 2 m crystallizes in the monoclinic system, space group P2 1 / n . The magnesium(II) cation is surrounded by six water molecules located at the apices of an almost regular octahedron with the mean Mg-O bond distance of 2.068 Å. The 2,6-PZDC anions are planar and are acceptors in a network of hydrogen bonds donated by the coordinated water molecules.     

2‐(4‐Acetyl‐3,5‐di­hydroxy‐2‐methyl­phenoxy)‐4,6‐di­methoxy‐3‐methyl­benzoic acid

In the title compound, C₁₉H₂₀O₈, the benzene rings are nearly perpendicular to each other [dihedral angle 80.2 (2)°]. The carboxy group is twisted out while both the methoxy and acetyl groups are almost coplanar with their attached benzene rings. The hydroxy group is involved in an intramolecular O—H?O hydrogen bond with the acetyl O atom and the compound is connected through an intermolecular O—H?O contact to form a dimer. The crystal structure is stabilized by intermolecular O—H?O hydrogen bonds.     

N‐Acetyl‐l‐tyrosine methyl ester monohydrate at 293 and 123 K

The crystal structure of a protected l ‐tyrosine, namely N‐acetyl‐l ‐tyrosine methyl ester monohydrate, C₁₂H₁₅NO₄·H₂O, was determined at both 293 (2) and 123 (2) K. The structure exhibits a network of O—H...O and N—H...O hydrogen bonds, in which the water molecule plays a crucial role as an acceptor of one and a donor of two hydrogen bonds. Molecules of water and of the protected l ‐tyrosine form hydrogen‐bonded layers perpendicular to [001]. C—H...π interactions are observed in the hydrophobic regions of the structure. The structure is similar to that of N‐acetyl‐l ‐tyrosine ethyl ester monohydrate [Soriano‐García (1993). Acta Cryst. C 49 , 96–97].     

2,3‐Difluoro‐4‐formyl­phenyl­boronic acid

The mol­ecule of the title compound, 2,3‐F₂‐4‐(CHO)C₆H₂B(OH)₂ or C₇H₅BF₂O₃, contains a formyl group coplanar with the benzene ring. The boronic acid group is twisted with respect to the benzene ring plane. The mol­ecules are organized into infinite chains via inter­molecular O—H⋯O hydrogen bonds. These chains are additionally connected via strong O—H⋯O hydrogen bonds, producing a folded layer structure perpendicular to the a axis. These layers are paired due to B⋯F inter­actions.     

1‐(4‐Bromo­phenyl)‐2‐methyl‐4‐nitro‐1H‐imidazole: bifurcated Br⋯O halogen–nitro bonds

The crystal packing of the title compound, C₁₀H₈BrN₃O₂, is determined mainly by relatively strong bifurcated C—Br⋯O halogen–nitro bonds. Both O atoms are involved in this interaction in an almost symmetrical manner and the difference [0.078 (3) Å] between the Br⋯O contact lengths is one of the smallest found in similar compounds. Halogen bonds and weak hydrogen bonds connect mol­ecules into layers which are stacked along the [100] direction.     

An empirical potential for the O-H ⋯ O hydrogen bond: Part 2. Comparison with observed hydrogen bond geometries

The room temperature distribution of O-H ? O hydrogen bond geometries has been predicted by a Monte Carlo calculation, with an empirical potential energy function for the hydrogen bond. The results are compared with a recent survey of hydrogen bonds in carbohydrate crystal structures. The calculated and observed distributions of the O-H ? O angle have mean values of 165.5° and 167.1° respectively. Both the theoretical and experimental results suggest that short O ? H hydrogen bonds tend to be more linear than long O ? H bonds. The distribution of hydrogen bonding within the lone pair plane of the acceptor oxygen atom is predicted to be broader than the distribution perpendicular to this plane, in agreement with the experimental data. The empirical hydrogen bond function, in conjunction with the molecular mechanics program MMI, has also been used to predict the geometries of inter-residue hydrogen bonds in five disaccharides. The O ? H distances and O-H ? O angles are reproduced with r.m.s. deviations of 0.06 Å and 9° respectively.     

LCAO-MO-SCF-Calculations on the stability and Sterochernistry of hydrogen bonds

CNDO and INDO calculations were performed on numerous structures with hydrogen bonds of different strength. An almost linear relationship is found between the strength of weak hydrogen bonds and the amount of charge transfered.π-electrons and lone pairs are nearly equivalent in hydrogen bonding. The stereochemistry of hydrogen bonds is determined largely by additional interactions betweenσ-bonds of the two molecules. Since proton affinities are calculated too large by the CNDO method, an error is introduced in the potential curves for proton transfer in weak hydrogen bonds. In systems with strong hydrogen bonds both structures with the proton on the right and left have almost the same energy and hence the potential curves for proton transfer are free of the errors mentioned above.     

Synthesis and Crystal Structure of Diethyl (4,6-diamino-1,3,5-triazine-2-yl) phosphonate

1　INTRODUCTIONSomeoforganophosphoruscompounds,includingmanyheterocycliccompoundscontainingphosphonogroup,havegoodbioactivityinorganism[1].Duetotheirrela-tionwithbiochemical/biological,pharmacologicalandpesticidalresearch,hetero-cycliccompoundscontainingphosphonogrouphavebeensynthesizedbysomeofnewsyntheticmethods,inwhichseveralnewbuildingblockwereused,suchasβ-phos-phonicenemines,[2,3]isocyanomethylphosphonate,[4]β-functionalγ-oxo-alkylphos-phonates,[5]andacetylenicphosphonate.[6]Inourpr…     

Di(phenylpropylamino)gossypol: a derivative of the dimeric natural product gossypol

Di(phenylpropylamino)gossypol [systematic name: 2,2′‐bis{1,6‐dihydroxy‐5‐isopropyl‐8‐[(3‐phenylpropylamino)methylidene]naphthalen‐7‐one}, C₄₈H₅₂N₂O₆, was formed by reaction of the dimeric natural product gossypol with 3‐phenylpropylamine. The structure of this compound has its two naphthalene ring systems oriented approximately perpendicular to each other, and the two pendant phenylpropyl groups have different conformations. One of these side groups is considerably disordered at room temperature but less so at 120 K. The enantiomeric molecules form centrosymmetric dimers that are supported by intermolecular hydrogen bonds and by hydrophobic interactions between a pair of naphthalene rings. Two additional hydrogen bonds tie the dimer pairs into layers. Unlike gossypol and many gossypol Schiff base derivatives, the title compound crystallizes without the inclusion of solvent, which appears to occur because of the size and flexibility of its phenylpropyl pendent groups.     

Aqua(4,4′‐oxy­dibenzoato‐κO)­cadmium(II)

The Cd atom in the polymeric title compound, [Cd(C₁₄H₈O₅)(H₂O)]_n, is linked to four carboxyl O atoms and a water mol­ecule in a five‐coordinate coordination polyhedron that is midway between a square pyramid and a trigonal bipyramid. The Cd atom and the water molecules both lie on the same twofold axis and the central O atom of the 4,4′‐oxydibenzoate moiety lies on another twofold axis. Covalent Cd—O bonds lead to the formation of a layer architecture perpendicular to the twofold axis, the layers being held together by hydrogen bonds in the third direction.     

限制在疏水板中的新的六边形-四边形三层冰结构

对限制在两个光滑的疏水板间的水进行了分子动力学模拟,观察到了两种晶体结构,都满足冰规则．在1GPa的压强和1．0nm的板间距下获得的新的冰相是平坦的六边形-四边形三层冰．在此结构中,靠近板的两层（外层）中的水分子形成六边形环,中间层的水分子形成四边形环．对于外层的水分子,其四个氢键中的三个在同一层中,另一个氢键与中间层连接．对于中间层的水分子,四个氢键中的两个在同。层中,而另外两个氢键与两个不同的外层相连．虽然三层的形状不同,但其面密度却接近相等．另一种结构是在0．8nm的板问距和100MPa的侧向压下获得的平坦的六边形双层冰．模拟中的相变既有一阶相变,也有连续相变．     

4‐Hydro­xy‐ONN‐azoxy­benzene

The oxidation of 4‐hydroxy­azo­benzene provided a mixture of two azoxy compounds, which were separated by column chromatography. The isomer with the higher melting point appeared to belong to the α (ONN) series, as determined by X‐ray diffraction. The mol­ecule, C₁₂H₁₀N₂O₂, is almost planar. The benzene rings are twisted by 11.7 (2) (substituted) and 4.1 (1)° (unsubstituted) with respect to the ONN plane. The mol­ecules are connected to one another by strong O—H?O hydrogen bonds forming chains extended along [001], which are bound by much weaker C—H?O hydrogen bonds forming layers in the bc plane.     

Two isomorphous azastilbene derivatives: 1‐(2‐chlorobenzyl)‐4‐[(E)‐2‐(4‐hydroxyphenyl)ethenyl]pyridinium chloride and 1‐(2‐bromobenzyl)‐4‐[(E)‐2‐(4‐hydroxyphenyl)ethenyl]pyridinium bromide

The crystal structures of the two title (E)‐stilbazolium halogenates, C₂₀H₁₇ClNO⁺·Cl⁻ and C₂₀H₁₇BrNO⁺·Br⁻, are isomorphous, with an isostructurality index of 0.985. The azastyryl fragments are almost planar, with dihedral angles between the benzene and pyridine rings of ca 4.5°. The rings of the benzyl groups are, in turn, almost perpendicular to the azastyryl planes, with dihedral angles larger than 80°. The cations and anions are connected by O—H...X⁻ (X = halogen) hydrogen bonds. The halide anions are `sandwiched' between the charged pyridinium rings of neighbouring molecules, and weak C—H...O hydrogen bonds and C—H...X and C—H...π interactions also contribute to the crystal structures.