Strong Hydrogen Bonds (strong + hydrogen_bond)

Distribution by Scientific Domains

Selected Abstracts

The solid solution (Fe0.81Al0.19)(H2PO4)3 with a strong hydrogen bond

Nadia Belfguira
Single crystals of the solid solution iron aluminium tris(dihydrogenphosphate), (Fe0.81Al0.19)(H2PO4)3, have been prepared under hydrothermal conditions. The compound is a new monoclinic variety (,-form) of iron aluminium phosphate (Fe,Al)(H2PO4)3. The structure is based on a two-dimensional framework of distorted corner-sharing MO6 (M = Fe, Al) polyhedra sharing corners with PO4 tetrahedra. Strong hydrogen bonds between the OH groups of the H2PO4 tetrahedra and the O atoms help to consolidate the crystal structure. [source]

Theoretical study of the substituent effect on the intramolecular hydrogen bonds in di(4-hydroxycoumarin) derivatives

Tzvetan Mihaylov
Abstract Geometry optimization of ortho -, meta -, and para -pyridyl-substituted di(4-hydroxycoumarin) [di(4-HC)] was performed with the density functional theory (DFT) [B3LYP/6-31G(d)] method. Two asymmetrical intramolecular OH,O hydrogen bonds (HBs) stabilized the structures. The calculated single HB energies varied from ,62.56 to ,47.53 kJ mol,1 and pointed to a relative strong hydrogen bond in the systems studied. The 2- and 6-pyridyl substituents produced the largest geometrical changes in di(4-hydroxycoumarin) fragment. The highest total HB energy was found for 2-pyridyl-substituted and the lowest one for 6-pyridyl-substituted di(4-hydroxycoumarin). The HB energy variations were confirmed with rotational barrier method calculations. Both steric and electrostatic factors were found to be responsible for the HB asymmetry in the compounds studied. According to the molecular electrostatic potential (MEP) calculations the most preferred reactive site for electrophilic attack of pyridyl-substituted di(4-hydroxycoumarin)s are the pyridine nitrogen and the carbonyl oxygens, followed by the hydroxyl oxygens. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source]

First-principle studies of intermolecular and intramolecular catalysis of protonated cocaine

Chang-Guo Zhan
Abstract We have performed a series of first-principles electronic structure calculations to examine the reaction pathways and the corresponding free energy barriers for the ester hydrolysis of protonated cocaine in its chair and boat conformations. The calculated free energy barriers for the benzoyl ester hydrolysis of protonated chair cocaine are close to the corresponding barriers calculated for the benzoyl ester hydrolysis of neutral cocaine. However, the free energy barrier calculated for the methyl ester hydrolysis of protonated cocaine in its chair conformation is significantly lower than for the methyl ester hydrolysis of neutral cocaine and for the dominant pathway of the benzoyl ester hydrolysis of protonated cocaine. The significant decrease of the free energy barrier, ,4 kcal/mol, is attributed to the intramolecular acid catalysis of the methyl ester hydrolysis of protonated cocaine, because the transition state structure is stabilized by the strong hydrogen bond between the carbonyl oxygen of the methyl ester moiety and the protonated tropane N. The relative magnitudes of the free energy barriers calculated for different pathways of the ester hydrolysis of protonated chair cocaine are consistent with the experimental kinetic data for cocaine hydrolysis under physiologic conditions. Similar intramolecular acid catalysis also occurs for the benzoyl ester hydrolysis of (protonated) boat cocaine in the physiologic condition, although the contribution of the intramolecular hydrogen bonding to transition state stabilization is negligible. Nonetheless, the predictability of the intramolecular hydrogen bonding could be useful in generating antibody-based catalysts that recruit cocaine to the boat conformation and an analog that elicited antibodies to approximate the protonated tropane N and the benzoyl O more closely than the natural boat conformer might increase the contribution from hydrogen bonding. Such a stable analog of the transition state for intramolecular catalysis of cocaine benzoyl-ester hydrolysis was synthesized and used to successfully elicit a number of anticocaine catalytic antibodies. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 980,986, 2005 [source]

Molecular simulation of ammonia absorption in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N])

AICHE JOURNAL, Issue 9 2009
Wei Shi
Isotherms for ammonia absorption in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N]) are computed at temperatures ranging from 298 K to 348 K using osmotic ensemble Monte Carlo simulations. The results agree well with previous experimental measurements. Activity coefficients vary from 0.5 to 0.8, indicating negative deviations from Raoult's Law. The computed enthalpy of mixing ranges from ,2 to ,11 kJ/mol. Computed partial molar volumes are on the order of 25,30 cm3/mol. Energy and radial distribution analyses indicate that ammonia interacts more strongly with the cation than the anion, in contrast to observations made of other gases in ionic liquids such as CO2. The reason for this behavior is that ammonia forms a strong hydrogen bond with the ring hydrogen atoms of the cation. The simulations predict that strategies aimed at changing the solubility of ammonia should focus on altering the hydrogen bond donating ability of the cation, and that altering the anion will have more modest effects. It is shown that this hypothesis is consistent with available experimental data. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

The solid solution (Fe0.81Al0.19)(H2PO4)3 with a strong hydrogen bond

Nadia Belfguira
Single crystals of the solid solution iron aluminium tris(dihydrogenphosphate), (Fe0.81Al0.19)(H2PO4)3, have been prepared under hydrothermal conditions. The compound is a new monoclinic variety (,-form) of iron aluminium phosphate (Fe,Al)(H2PO4)3. The structure is based on a two-dimensional framework of distorted corner-sharing MO6 (M = Fe, Al) polyhedra sharing corners with PO4 tetrahedra. Strong hydrogen bonds between the OH groups of the H2PO4 tetrahedra and the O atoms help to consolidate the crystal structure. [source]

Strong asymmetric hydrogen bonding in 2-(oxamoylamino)ethylammonium oxamate,oxamic acid (1/1)

Marta Martinez Belmonte
The title compound, C4H10N3O2+·C2H2NO3,·C2H3NO3, contains at least 11 distinct hydrogen-bond interactions showing a great variety of bond strengths. The shortest and strongest hydrogen bond [O...O = 2.5004,(12),Å] is found between the uncharged oxamic acid molecule and the oxamate monoanion. The grouping formed by such a strong hydrogen bond can thus be considered as a hydrogen bis(oxamate) monoanion. It lacks crystallographic symmetry and the two oxamate groups have different conformations, showing an asymmetric hydrogen-bond interaction. Significantly, the asymmetry allows us to draw a direct comparison of site basicity for the two inequivalent carboxylate O atoms in the planar oxamate anion. The constituent molecular ions of (I) form ribbons, where all amide and carboxylate groups are coplanar. Graph-set analysis of the hydrogen-bonded networks reveals the R22(10) and R22(9) homodromic nets as important structure-directing motifs, which appear to be a common feature of many oxamate-containing compounds. [source]

Anion-Directed Template Synthesis and Hydrolysis of Mono-Condensed Schiff Base of 1,3-Pentanediamine and o -Hydroxyacetophenone in NiII and CuII Complexes

Pampa Mukherjee
Abstract Bis(o -hydroxyacetophenone)nickel(II) dihydrate, on reaction with 1,3-pentanediamine, yields a bis-chelate complex [NiL2]·2H2O (1) of mono-condensed tridentate Schiff baseligand HL {2-[1-(3-aminopentylimino)ethyl]phenol}. The Schiff base has been freed from the complex by precipitating the NiII as a dimethylglyoximato complex. HL reacts smoothly with Ni(SCN)2·4H2O furnishing the complex [NiL(NCS)] (2) and with CuCl2·2H2O in the presence of NaN3 or NH4SCN producing [CuL(N3)]2 (3) or [CuL(NCS)] (4). On the other hand, upon reaction with Cu(ClO4)2·6H2O and Cu(NO3)2·3H2O, the Schiff base undergoes hydrolysis to yield ternary complexes [Cu(hap)(pn)(H2O)]ClO4 (5) and [Cu(hap)(pn)(H2O)]NO3 (6), respectively (Hhap = o -hydroxyacetophenone and pn = 1,3-pentanediamine). The ligand HL undergoes hydrolysis also on reaction with Ni(ClO4)2·6H2O or Ni(NO3)2·6H2O to yield [Ni(hap)2] (7). The structures of the complexes 2, 3, 5, 6, and 7 have been confirmed by single-crystal X-ray analysis. In complex 2, NiII possesses square-planar geometry, being coordinated by the tridentate mono-negative Schiff base, L and the isothiocyanate group. The coordination environment around CuII in complex 3 is very similar to that in complex 2 but here two units are joined together by end-on, axial-equatorial azide bridges to result in a dimer in which the geometry around CuII is square pyramidal. In both 5 and 6, the CuII atoms display the square-pyramidal environment; the equatorial sites being coordinated by the two amine groups of 1,3-pentanediamine and two oxygen atoms of o -hydroxyacetophenone. The axial site is coordinated by a water molecule. Complex 7 is a square-planar complex with the Ni atom bonded to four oxygen atoms from two hap moieties. The mononuclear units of 2 and dinuclear units of 3 are linked by strong hydrogen bonds to form a one-dimensional network. The mononuclear units of 5 and 6 are joined together to form a dimer by very strong hydrogen bonds through the coordinated water molecule. These dimers are further involved in hydrogen bonding with the respective counteranions to form 2-D net-like open frameworks. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

(Pyrazole)silver(I) and -gold(I) Complexes with Strong and Weak Hydrogen-Bonding Interactions as the Basis of One- or Two-Dimensional Structures

M. Luz Gallego
Abstract New AuI/AgI complexes containing one or two substituted pyrazole ligands [Au(Hpzbp2)(PPh3)](p -CH3C6H4SO3) [Hpzbp2 = 3,5-bis(4- n -butoxyphenyl)pyrazole] (1) and [M(HpzR2)2]nX [HpzR2 = Hpzbp2, M = Au, n = 1, X = p -CH3C6H4SO3 (2), NO3, (3); n = 2, X = 1,5-naphthalenedisulfonate (1,5nds) (4); HpzR2 = Hpzbp2, M = Ag, n = 1, X = BF4, (5), CF3SO3, (6); HpzR2 = HpzNO2 (3,5-dimethyl-4-nitropyrazole), M = Ag, n = 1, X = BF4, (7), CF3SO3, (8)], have been prepared and characterized. Compounds 1, 2, 5 and 8 have been proved to be useful for supramolecular assembly from their single X-ray diffraction analysis. In all cases strong hydrogen bonds maintain the cationic units bonded to their corresponding counterions. The crystal packing arrangement of 1, 2 and 5 is, however, determined by weak C,H···O/F hydrogen-bonding interactions involving the remaining O/F atoms of the counterion. By contrast, for 8 a two-dimensional layer-type polymeric network is formed by ,···, (NO2···NO2) and coordinative Ag···O interactions in which the NO2 substituent on the pyrazole is implicated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

Synthesis of Dicarboxylate "C-Clamp" 1,2-Diethynylarene Compounds as Potential Transition-Metal Ion Hosts

Erwin Reisner
Abstract We report an efficient convergent synthesis of a new type of C-clamp ligand with a 1,2-diethynylarene scaffold involving a chelate host capable of binding a guest molecule in its endo -dicarboxylate pocket. The chemistry involves a combination of palladium-catalyzed Sonogashira, Heck, and Suzuki cross-coupling reactions. The compounds 2,3-bis[2-(2,-carboxybiphenyl-4-yl)ethynyl]triptycene and 4,5-bis[2-(2,-carboxybiphenyl-4-yl)ethynyl]veratrole and their 2,-carboxy- m -terphenyl-4-yl analogues were designed as dinucleating ligands to assemble carboxylate-bridged transition-metal complexes with a windmill geometry. The X-ray crystal structure of one such C-clamp compound containing co-crystallized water molecules reveals strong hydrogen bonds of the aqua guest to the endo -oriented carboxylic acid entities of the C-clamp host. In addition, two syn -N-donor ligands were prepared as a synthetic scaffold to mimic the geometric arrangement of N-donor atoms in carboxylate-bridged dinuclear proteins. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Preparation and properties of the single-walled carbon nanotube/cellulose nanocomposites using N -methylmorpholine- N -oxide monohydrate

Dong-Hun Kim
Abstract Single-walled carbon nanotube (SWNT)/cellulose nanocomposite films were prepared using N -methylmorpholine- N -oxide (NMMO) monohydrate as a dispersing agent for the acid-treated SWNTs (A-SWNTs) as well as a cellulose solvent. The A-SWNTs were dispersed in both NMMO monohydrate and the nanocomposite film (as confirmed by scanning electron microscopy) because of the strong hydrogen bonds of the A-SWNTs with NMMO and cellulose. The mechanical properties, thermal properties, and electric conductivity of the nanocomposite films were improved by adding a small amount of the A-SWNTs to the cellulose. For example, by adding 1 wt % of the A-SWNTs to the cellulose, tensile strain at break point, Young's modulus, and toughness increased , 5.4, , 2.2, and , 6 times, respectively, the degradation temperature increased to 9°C as compared with those of the pure cellulose film, and the electric conductivities at , (the wt % of A-SWNTs in the composite) = 1 and 9 were 4.97 × 10,4 and 3.74 × 10,2 S/cm, respectively. Thus, the A-SWNT/cellulose nanocomposites are a promising material and can be used for many applications, such as toughened Lyocell fibers, transparent electrodes, and soforth. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Highly Ordered Interstitial Water Observed in Bone by Nuclear Magnetic Resonance,

Erin E Wilson
Abstract NMR was used to study the nanostructure of bone tissue. Distance measurements show that the first water layer at the surface of the mineral in cortical bone is structured. This water may serve to couple the mineral to the organic matrix and may play a role in deformation. Introduction: The unique mechanical characteristics of bone tissue have not yet been satisfactorily connected to the exact molecular architecture of this complex composite material. Recently developed solid-state nuclear magnetic resonance (NMR) techniques are applied here to the mineral component to provide new structural distance constraints at the subnanometer scale. Materials and Methods: NMR dipolar couplings between structural protons (OH, and H2O) and phosphorus (PO4) or carbon (CO3) were measured using the 2D Lee-Goldburg Cross-Polarization under Magic-Angle Spinning (2D LG-CPMAS) pulse sequence, which simultaneously suppresses the much stronger proton-proton dipolar interactions. The NMR dipolar couplings measured provide accurate distances between atoms, e.g., OH and PO4 in apatites. Excised and powdered femoral cortical bone was used for these experiments. Synthetic carbonate (,2-4 wt%)-substituted hydroxyapatite was also studied for structural comparison. Results: In synthetic apatite, the hydroxide ions are strongly hydrogen bonded to adjacent carbonate or phosphate ions, with hydrogen bond (O-H) distances of ,1.96 Å observed. The bone tissue sample, in contrast, shows little evidence of ordered hydroxide. Instead, a very ordered (structural) layer of water molecules is identified, which hydrates the small bioapatite crystallites through very close arrangements. Water protons are ,2.3-2.55 Å from surface phosphorus atoms. Conclusions: In synthetic carbonated apatite, strong hydrogen bonds were observed between the hydroxide ions and structural phosphate and carbonate units in the apatite crystal lattice. These hydrogen bonding interactions may contribute to the long-range stability of this mineral structure. The biological apatite in cortical bone tissue shows evidence of hydrogen bonding with an ordered surface water layer at the faces of the mineral particles. This structural water layer has been inferred, but direct spectroscopic evidence of this interstitial water is given here. An ordered structural water layer sandwiched between the mineral and the organic collagen fibers may affect the biomechanical properties of this complex composite material. [source]

Towards the best model for H atoms in experimental charge-density refinement

Anna A. Hoser
The consequences of different treatments of H atoms in experimental charge-density studies are discussed. Geometric and topological parameters obtained after applying four different H-atom models in multipolar refinement on high-resolution X-ray data only were compared with the results obtained for a reference joint high-resolution X-ray/neutron refinement. The geometry and the topological critical point and integrated parameters closest to the reference values were obtained after a mixed refinement (high-order refinement of heavy atoms, low-angle refinement of H atoms and elongation of the X,H distance to the average neutron bond lengths) supplemented by an estimation of the anisotropic thermal motions of H atoms using the SHADE program. Such a procedure works very well even for strong hydrogen bonds. The worst fit to the reference results for both critical point and integrated parameters was obtained when only the standardization to the average neutron X,H distances was applied. The non-H-atom parameters are also systematically influenced by the H-atom modeling. In order to compare topological and integrated properties calculated for H and non-H atoms in multipolar refinement when there are no neutron data, the same treatment of H atoms (ideally the mixed refinement + estimated anisotropic atomic displacement parameters for H atoms) should be applied. [source]

Monitoring structural transformations in crystals.


Structural changes proceeding in a crystal during the Yang photocyclization of the salt 6,6-diethyl-5-oxo-5,6,7,8-tetrahydronaphthalene-2-carboxylate with (1S)-1-(4-methylphenyl)ethylamine were monitored by means of X-ray structure analysis. The course of the photoreaction was evaluated on the basis of the geometrical parameters for the pure reactant crystal. Variations in the cell constants, the product content, the geometry of the reaction centre, the orientation of molecular fragments and the geometry of hydrogen bonds were described and analyzed. It was found that the cell volume increased until 56% product content and decreased thereafter. The distance between the directly reacting C atoms was constant, ,,3.0,Å, until ,,75% reaction progress. Analysis of the distance between atoms that would participate in the formation of the second (unobserved) enantiomorph excluded the formation of such an isomer. Molecular fragments varied their orientation during the photoreaction, and the largest change was observed for the carboxylate group despite its participation in strong hydrogen bonds. The geometry of the hydrogen bonds changed during the photoreaction. The largest change was 0.17,Å for the D...A distance and 13° for the D,H...A angle. A comparison of the intra- and intermolecular parameters for the studied salt with data for other compounds undergoing the Yang photocyclization in crystals revealed a diversity of structural changes brought about by this type of photochemical reaction. [source]

Structural changes of hexamethylenetetramine and undecanedioic acid co-crystal (HMT-C11) as a function of the temperature

Carlos Basílio Pinheiro
HMT-C11 belongs to the family of adducts formed by the co-crystallization of N4(CH2)6 molecules (hexamethylenetetramine or HMT) and aliphatic dicarboxylic acids HOOC(CH2)n, 2COOH with 5 ,n, 13 (Cn). The adducts exhibit a layered structure in which the packing between HMT and Cn is determined by strong hydrogen bonds. The compounds in this family studied so far present thermotropic structural phase transitions and, depending on the chain length, disordered, twinned and modulated phases. The structure refinement of HMT-C11 based on X-ray diffraction experiments indicates three distinct phases from the melting point down to liquid nitrogen temperature: phase I is not crystalline; phase II is disordered (stacking fault) and its average structure is described in space group Bmmb; phase III is partially disordered and its symmetry is P21/c. The systematic study of the structure evolution of phase III upon cooling revealed that the disorder has a dynamic character (anharmonicity). The main structural change observed from 293,K down to 93,K is the increase of the tilting angle of the C11 chains relative to the layer plane and the rotation of the HMT molecules. Both HMT and C11 behave like rigid bodies in the temperature range investigated. The quality of the refinements leads to a conclusive model for the O,H,N hydrogen bonds linking HMT and C11. [source]

Similarities and differences between bis[2-(bromomethyl)phenyl] diselenide, bis[2-(chloromethyl)phenyl] diselenide and bis[2-(hydroxymethyl)phenyl] diselenide

Alberth Lari
The title compounds, C14H12Br2Se2, (I), C14H12Cl2Se2, (II), and C14H14O2Se2, (III), feature a diselenide bridge between two o -benzyl bromide [in (I)], two o -benzyl chloride [in (II)] or two o -benzyl alcohol units [in (III)]. In the molecular structure of (I) and in both independent molecules of (II), close contacts are observed between the halogen centres and the diselenide unit. In the case of modification (IIIa), strong hydrogen bonds between the ,OH groups dominate, whereas the molecular structures of modification (IIIb) and bis{2-[(dimethylamino)methyl]phenyl} diselenide, C18H24N2Se2, (IV), are comparable with those of (I) and (II). A correlation between the strength of the contacts and the angle between the benzene planes and the Se,Se units is found. [source]

A structural systematic study of four isomers of difluoro- N -(3-pyridyl)benzamide

Joyce McMahon
The four isomers 2,4-, (I), 2,5-, (II), 3,4-, (III), and 3,5-difluoro- N -(3-pyridyl)benzamide, (IV), all with formula C12H8F2N2O, display molecular similarity, with interplanar angles between the C6/C5N rings ranging from 2.94,(11)° in (IV) to 4.48,(18)° in (I), although the amide group is twisted from either plane by 18.0,(2),27.3,(3)°. Compounds (I) and (II) are isostructural but are not isomorphous. Intermolecular N,H...O=C interactions form one-dimensional C(4) chains along [010]. The only other significant interaction is C,H...F. The pyridyl (py) N atom does not participate in hydrogen bonding; the closest H...Npy contact is 2.71,Å in (I) and 2.69,Å in (II). Packing of pairs of one-dimensional chains in a herring-bone fashion occurs via,-stacking interactions. Compounds (III) and (IV) are essentially isomorphous (their a and b unit-cell lengths differ by 9%, due mainly to 3,4-F2 and 3,5-F2 substitution patterns in the arene ring) and are quasi-isostructural. In (III), benzene rotational disorder is present, with the meta F atom occupying both 3- and 5-F positions with site occupancies of 0.809,(4) and 0.191,(4), respectively. The N,H...Npy intermolecular interactions dominate as C(5) chains in tandem with C,H...Npy interactions. C,H...O=C interactions form R22(8) rings about inversion centres, and there are ,,, stacks about inversion centres, all combining to form a three-dimensional network. By contrast, (IV) has no strong hydrogen bonds; the N,H...Npy interaction is 0.3,Å longer than in (III). The carbonyl O atom participates only in weak interactions and is surrounded in a square-pyramidal contact geometry with two intramolecular and three intermolecular C,H...O=C interactions. Compounds (III) and (IV) are interesting examples of two isomers with similar unit-cell parameters and gross packing but which display quite different intermolecular interactions at the primary level due to subtle packing differences at the atom/group/ring level arising from differences in the peripheral ring-substitution patterns. [source]

Two isomorphous cobalt(II) complexes: poly[[diaqua-,-2,5-dicarboxybenzene-1,4-dicarboxylato-,-1,2-di-4-pyridylethene-cobalt(II)] 1,2-di-4-pyridylethene solvate] and the 1,2-di-4-pyridylethane analogue

Ana María Atria
The two isomorphous title structures, formulated as {[Co(C10H4O8)(C12H10N2)(H2O)2]·C12H10N2}n, (I), and {[Co(C10H4O8)(C12H12N2)(H2O)2]·C12H12N2}n, (II), respectively, are reported. They crystallize in the space group P with only one formula unit in the asymmetric unit, so that the organic ligands lie about inversion centres and the Co atom lies on an inversion centre. The Co atoms are octahedrally coordinated by a carboxylate O atom from 2,5-dicarboxybenzene-1,4-dicarboxylate (H2btc), one N atom from 1,2-di-4-pyridylethene (L) in (I) or from 1,2-di-4-pyridylethane (L) in (II), and one coordinated water molecule, plus their inversion-related species. This particular coordination results in a two-dimensional array, with an elemental unit in the shape of a parallelogram having the CoII cations at the corners, linked in one direction by L bridges and in the opposite direction by H2btc groups. The L solvent molecules act as pillars between parallel planes, linking them by strong hydrogen bonds where the H atoms lie midway between the formal donor/acceptor atoms in a `shared' mode. Comparison is made with structures presenting the same structural motif, strongly suggesting that the two-dimensional arrangement reported here might be a very stable robust building block for molecular engineering purposes. [source]

Hydrogen bonding in 2-(2-oxothiazolidin-3-yl)-4,5-dihydrothiazolium hydrogen sulfate monohydrate

Rodrigo S. Corrêa
The asymmetric unit of the title compound, C6H9N2OS2+·HSO4,·H2O, contains a heterocyclic cation, a hydrogen sulfate anion and a water molecule. There are strong hydrogen bonds between the hydrogen sulfate anions and water molecules, forming an infinite chain along the [010] direction, from which the cations are pendent. The steric, electronic and geometric features are compared with those of similar compounds. In this way, structural relationships are stated in terms of the influence of the sulfate group on the protonation of the heterocycle and on the tautomeric equilibrium in the solid state. [source]

Form I of desloratadine, a tricyclic anti­histamine

Prashant M. Bhatt
The title compound [systematic name: 8-chloro-11-(piperidin-4-yl­idene)-6,11-dihydro-5H -benzo[4,5]cyclo­hepta­[2,1- b]pyridine], C19H19ClN2, was crystallized from ethyl acetate. The inter­esting feature of the reported structure is that it does not contain any strong hydrogen bonds, although the mol­ecule contains a secondary NH group, which is a good hydrogen-bond donor. [source]

Aqua­(thio­sulfato-,2O,S)[2,4,6-tri-2-pyridyl-1,3,5-triazine-,3N2,N1,N6]zinc(II) hemihydrate

Sergio Baggio
The title compound, [Zn(S2O3)(C18H12N6)(H2O)]·0.5H2O, contains two almost identical independent monomeric moieties composed of an octa­hedral Zn centre coordinated by a tridentate 2,4,6-tri-­2-pyridyl-1,3,5-triazine (tpt) ligand, one aqua ligand and an O,S -chelating thio­sulfate anion. The structure is stabilized by a solvent water mol­ecule. Multiple strong hydrogen bonds with additional weaker ,,, inter­actions between tpt groups define a multiple column spatial organization. [source]

Theoretical and experimental study of the complexation of valinomycin with ammonium cation

BIOPOLYMERS, Issue 12 2008
í Dybal
Abstract The interactions of valinomycin, macrocyclic depsipeptide antibiotic ionophore, with ammonium cation NH4+ have been investigated. Using quantum mechanical density functional theory (DFT) calculations, the most probable structure of the valinomycin-NH4+ complex species was predicted. In this complex, the ammonium cation is bound partly by three strong hydrogen bonds to three ester carbonyl oxygen atoms of valinomycin and partly by somewhat weaker hydrogen bonds to the remaining three ester carbonyl groups of the valinomycin ligand. The strength of the valinomycin-NH4+ complex was evaluated experimentally by capillary affinity electrophoresis. From the dependence of valinomycin effective electrophoretic mobility on the ammonium ion concentration in the background electrolyte, the apparent binding (association, stability) constant (Kb) of the valinomycin-NH4+ complex in methanol was evaluated as log Kb = 1.52 ± 0.22. © 2008 Wiley Periodicals, Inc. Biopolymers 89: 1055,1060, 2008. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at [source]

Structure and Dynamics of Water Confined in Dimethyl Sulfoxide

CHEMPHYSCHEM, Issue 1 2006
A. Wulf
Abstract We study the structure and dynamics of hydrogen-bonded complexes of H2O/D2O and dimethyl sulfoxide (DMSO) by infrared spectroscopy, NMR spectroscopy and ab initio calculations. We find that single water molecules occur in two configurations. For one half of the water monomers both OH/OD groups form strong hydrogen bonds to DMSO molecules, whereas for the other half only one of the two OH/OD groups is hydrogen-bonded to a solvent molecule. The H-bond strength between water and DMSO is in the order of that in bulk water. NMR deuteron relaxation rates and calculated deuteron quadrupole coupling constants yield rotational correlation times of water. The molecular reorientation of water monomers in DMSO is two-and-a-half times slower than in bulk water. This result can be explained by local structure behavior. [source]

Probing the Vibrations of Shared, OH+O-Bound Protons in the Gas Phase

CHEMPHYSCHEM, Issue 5 2004
David T. Moore Dr.
Spectral signature of a proton bridge? Gas-phase infrared spectra are reported in the range of 500,1800 cm,1 for three species with short, strong hydrogen bonds, namely the proton-bound dimers of dimethyl ether (shown in the picture) and diethyl ether, and protonated 1,1,-oxybis[2-methoxyethane] (diglyme). The spectra are all quite similar, and furthermore they also strongly resemble the spectrum of the proton-bound water dimer (H5O2+), suggesting that there may be a conserved "spectral signature" for a proton bound between two oxygen atoms. [source]

Synthesis, Structure, Thermal and Magnetic Properties of a New Open-framework Borophosphate: NH4Mn(H2O)2BP2O8·H2O,

Heng-Zhen Shi
Abstract Using new template agent, a new borophosphate compound, NH4Mn(H2O)2BP2O8·H2O was hydrothermally prepared and structurally characterized. It crystallizes in a hexagonal space group P6122 with lattice parameters a=0.9652(2) nm, c=1.5792(5) nm, V=1.2740(5) nm3 and Z=6. The structure has a three-dimensional open-frame work with borophosphate helical ribbons 1,{[BP2O8]3, and MnO4(H2O)2 octahedra. The water molecules are positioned inside the helical channels. Very interestingly, the ammonium ions are located outside the loop of the free helical ribbons via the strong hydrogen bonds, which is different from the borophosphate analogue reported. The magnetization of the title compound is paramagnetic down to 5 K of the Curie-Weiss type within the measured range of 5,300 K with ,=,7.3 K, indicative of very weak antiferromagnetic interactions. The thermal decomposition of the compound was also described. [source]

Luminescent Property of a Supramolecular Silver(I)-Thiolate Complex Based on Secondary Ag-S Interactions and Hydrogen Bonds

Wei-Ping Su
Abstract The supramolecular silver(I)-thiolate complex [Ag(,2 -SC4N2H4)2(SCN)]n has been prepared from the reaction of AgSCN and pyrimidine-2-thiol in DMF. X-ray diffraction analysis shows that the supramolecular structure exhibits one-dimensional chain through the secondary Ag-S interactions and the chains are further linked by strong hydrogen bonds to form a three dimensional network. The luminescence effect from the silver-centered state of S,Ag LMCT in solid state is different from that in solution due to the secondary Ag-S interactions. [source]