Search results for "BOND"
showing 10 items of 3527 documents
Mononuclear coordination compounds based on a novel chelating triazole ligand: 1-vinyl-3-acetylamino-1,2,4-triazole
2002
The synthesis, X-ray structure, magnetic and spectroscopic properties of new Co(II), Ni(II) and Cu(II) complexes with 1-vinyl-3-acetylamino-1,2,4-triazole (vaat) are reported. The crystal structures of [Ni(vaat)2(H2O)2](NO3)2 and [Cu(vaat)2(H2O)2]Cl2 have been determined by X-ray diffraction. In these mononuclear complexes, the metal ion is surrounded by two water molecules in axial positions and two oxygen and two nitrogen (N4) atoms coming from two trans-oriented chelating vaat molecules. Anions are noncoordinated and are involved in a hydrogen bonding network. The complex cations of [Cu(vaat)2(H2O)2]Cl2 are aligned within chains. In the structure of [Ni(vaat)2(H2O)2](NO3)2 the nitrate an…
Influence of Crystallization Additives on Morphology of Selected Benzoic Acids - A Molecular Dynamics (MD) Simulation Study
2021
Two model substances were used in the study – 2,6-dimethoxybenzoic acid (2,6MeOBA) and 3-hydroxybenzoic acid (3OHBA), each having two polymorphic forms, including a form without carboxylic acid homodimers in their crystal structure. For each polymorph 2-3 largest crystal faces were selected for MD simulations and the crystal was cut along these planes by preparing simulation box with these planes facing towards solution. In the performed study it was determined which additives potentially can influence the crystal morphology (based on the selected planes) and possibly also the obtained polymorph achieved by significantly changing crystal growth rate by adsorbing on the surface. For the stud…
Calix[4]arenes with resorcinol units incorporated in 2,6-position
1990
Abstract Calix[4]arenes containing one or two resorcinol units incorporated via their 2,6-positions were prepared by fragment condensation. Due to the cyclic array of intramolecular hydrogen bonds these molecules assume the cone-conformation.
(S,S,S,S)-Nebivolol hydro-chloride hemihydrate.
2012
The asymmetric unit of the title hydrated salt, C22H26F2NO4+·Cl−·0.5H2O, consists of an (S,S,S,S)-nebivolol {nebivol = bis[2-(6-fluoro-3,4-dihydro-2H-1-benzopyran-2-yl)-2-hydroxyethyl]ammonium} cation, a chloride anion and a half-occupancy water molecule. The dihedral angle between the mean planes of the benzene rings is 50.34 (12)°. The pyran rings adopt half-chair conformations. The crystal packing features O—H...O hydrogen bonds and weak N—H...Cl, O—H...Cl, and O—H...Cl interactions, producing layers along (010).
Non-classical CH⋯O hydrogen-bond determining the regio- and stereoselectivity in the [3 + 2] cycloaddition reaction of (Z)-C-phenyl-N-methylnitrone w…
2015
The role of the ester groups in the regio- and stereoselectivities of the zw-type [3 + 2] cycloaddition (32CA) reaction of C-phenyl-N-methylnitrone with dimethyl 2-benzylidenecyclopropane-1,1-dicarboxylate (BCPC) has been studied using DFT methods at the MPWB1K/6-31G(d) level. The possible ortho/meta regioisomeric channels and the endo/exo stereoselective approach modes were explored and characterized. Analysis of the relative energies associated with the different reaction pathways indicates that the presence of the two CO2Me groups in the cyclopropane ring has a remarkable effect on selectivities favouring the ortho/endo path, in good agreement with the experimental data. Inclusion of sol…
The effect of pH on polymorph formation of the pharmaceutically active compound tianeptine.
2012
The anti-depressant pharmaceutical tianeptine has been investigated to determine the dynamics of polymorph formation under various pH conditions. By varying the pH two crystalline polymorphs were isolated. The molecular and crystal structures have been determined to identify the two polymorphs. One polymorph is an amino carboxylic acid and the other polymorph is a zwitterion. In the solid state the tianeptine moieties are bonded through hydrogen bonds. The zwitterion was found to be less stable and transformed to the acid form. During this investigation an amorphous form was identified.
Unexpected Structural Diversity in Alkali Metal Azide-Crown Ether Complexes: Syntheses, X-ray Structures, and Quantum-Chemical Calculations
2005
A series of alkali metal azide-crown ether complexes, [Li([12]crown-4)(N-3)], [Na([15]crown-5)(N-3)], [Na([15]crown-5)(H2O)(2)]N-3, [K([18]crown-6)(N-3)(H2O)], [Rb([18]crown-6)(N-3)(H2O)], [Cs([18]crown-6)(N-3)](2), and [Cs([18]crown-6)(N-3)(H2O)(MeOH)], has been synthesised. In most cases, single crystals were obtained, which allowed X-ray crystal structures to be derived. The structures obtained have been compared with molecular structures computed by density functional theory (DFT) calculations. This has allowed the effects of the crystal lattice on the structures to be investigated. Also, a study of the M-N-terminal metalazide bond length and charge densities on the metal (M) and termin…
5-Amino-1-phenyl-3-trifluoromethyl-1H-pyrazole-4-carboxylic acid
2009
In the title compound, C11H8F3N3O2, there are two molecules in the asymmetric unit wherein the phenyl rings make dihedral angles of 65.3 (2) and 85.6 (2)° with the pyrazole rings. In the crystal, pairs of molecules are held together by O—H...O hydrogen bonds between the carboxyl groups, forming a centrosymmetric dimer with an R22(8) motif. Intramolecular N—H...O interactions are also present.
The Synergetic Interplay of Weak Interactions in the Ion-Pair Recognition of Quaternary and Diquaternary Ammonium Salts by Halogenated Resorcinarenes
2013
The influence of halogens on the noncovalent interactions of different upper-rim-substituted hexylresorcinarenes with quaternary and diquaternary ammonium iodide salts was investigated in the gas phase by electrospray ionization Fourier-transform ion-cyclotron-resonance (ESI-FTICR) mass spectrometry and in solution by 1H NMR titration studies. The electronic nature of the substituents on the upper rim of the resorcinarene was directly reflected in the order of binding strengths of the hosts towards quaternary and diquaternary ammonium cations in the gas phase. In solution, the opposite trend was observed, with generally higher binding constants for the diquaternary over the quaternary salts…
N-[(1S,2S)-2-Amino-1,2-diphenylethyl]-4-methylbenzenesulfonamide [(S,S)-TsDPEN]
2010
The crystal structure of the title compound, C21H22N2O2S, shows a network of N—H...N and N—H...O hydrogen bonds. The tolyl and 1-phenyl rings are almost mutually coplanar [7.89 (9)°], while the 2-phenyl ring makes a dihedral angle of 50.8 (1) ° with the 1-phenyl ring. An intramolecular N—H...N hydrogen bond stabilizes the molecular conformation.