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Hydrogen-bond Motif (hydrogen-bond + motif)

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Chemistry100%

Selected Abstracts

Hydrogen-bond motifs in N -monosubstituted derivatives of barbituric acid: 5-allyl-5-isopropyl-1-methylbarbituric acid (enallylpropymal) and 1,5-di(but-2-enyl)-5-ethylbarbituric acid

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2010
Thomas Gelbrich
Both title structures exhibit essentially planar barbiturate rings. The crystal structure of enallylpropymal (5-allyl-5-isopropyl-1-methylbarbituric acid), C11H16N2O3, is composed of centrosymmetric N,H...O hydrogen-bonded dimers, while 1,5-di(but-2-enyl)-5-ethylbarbituric acid, C14H20N2O3, forms N,H...O hydrogen-bonded helical chains. Each of the ten known crystal structures of closely related N -monosubstituted derivatives of barbituric acid displays one of the fundamental N,H...O hydrogen-bonded motifs of the two title structures, i.e. either a dimer or a chain. [source]

Hydrogen bonding in enantiomeric versus racemic mono-carboxylic acids; a case study of 2-phenoxy­propionic acid

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2003
Henning Osholm Sørensen
The structural and thermodynamic backgrounds for the crystallization behaviour of racemates have been investigated using 2-phenoxypropionic acid (PPA) as an example. The racemate of PPA behaves normally and forms a racemic compound that has a higher melting point and is denser than the enantiomer. Low-temperature crystal structures of the pure enantiomer, the enantiomer cocrystallized with n -alkanes and the racemic acid showed that hydrogen-bonded dimers that form over crystallographic symmetry elements exist in all but the structure of the pure enantiomer. A database search for optically pure chiral mono-carboxylic acids revealed that the hydrogen-bonded cyclic dimer is the most prevalent hydrogen-bond motif in chiral mono-carboxylic acids. The conformation of PPA depends on the hydrogen-bond motif; the antiplanar conformation relative to the ether group is associated with a catemer hydrogen-bonding motif, whereas the more abundant synplanar conformation is found in crystals that contain cyclic dimers. Other intermolecular interactions that involve the substituent of the carboxylic group were identified in the crystals that contain the cyclic dimer. This result shows how important the nature of the substituent is for the crystal packing. The differences in crystal packing have been related to differences in melting enthalpy and entropy between the racemic and enantiomeric acids. In a comparison with the equivalent 2-(4-chlorophenoxy)-propionic acids, the differences between the crystal structures of the chloro and the unsubstituted acid have been identified and related to thermodynamic data. [source]

Three-dimensional supramolecular architecture in imidazolium hydrogen 2,3,5,6-tetrafluoroterephthalate

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2010
Li-Li Yu
The asymmetric unit of the title salt formed between 2,3,5,6-tetrafluoroterephthalic acid (H2tfbdc) and imidazolium (ImH), C3H5N2+·C8HF4O4,, contains one Htfbdc, anion and one ImH2+ cation, joined by a classical N,H...O hydrogen bond. The acid and base subunits are further linked by N,H...O and O,H...O hydrogen bonds into infinite two-dimensional layers with R56(32) hydrogen-bond motifs. The resulting (4,4) network layers interpenetrate to produce an interlocked three-dimensional structure. The final three-dimensional supramolecular architecture is further stabilized by the linkages of two C,H...O interactions. [source]

Two three-dimensional networks in the binary molecular adducts 4-methylimidazolium hydrogen terephthalate and bis(4-methylimidazolium) terephthalate

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2008
Xiang-Gao Meng
Both the 1:1 and 2:1,molecular adducts of 4-methylimidazole (4-MeIm) and terephthalic acid (H2TPA) are organic salts, viz. C4H7N2+·C8H5O4,, (I), and 2C4H7N2+·C8H4O42,, (II), respectively. The component ions in (I) are linked by N,H...O and O,H...O hydrogen bonds into continuous two-dimensional layers built from R64(32) hydrogen-bond motifs running parallel to the (100) plane. These adjacent two-dimensional layers are in turn linked by a combination of C,H...O, C,H..., and ,,, interactions into a three-dimensional network. In the crystal structure of (II), with the anion located on an inversion centre, only N,H...O hydrogen bonds result in two-dimensional layers built from R88(42) hydrogen-bond motifs running parallel to the (102) plane. Being similar to those in (I), these layers are also linked by means of C,H...O, C,H..., and ,,, interactions, forming a three-dimensional network. This study indicates that, on occasion, a change of the reactant concentration can exert a pivotal influence on the construction of supramolecular structures based on hydrogen bonds. [source]