1,721,019 research outputs found
Probing the structure of framework materials by high pressure and the example of a magnetic, non-porous coordination polymer
No full textStructural Elucidation of α-Cyclodextrin-Succinic Acid Pseudo Dodecahydrate: Expanding the Packing Types of α-Cyclodextrin Inclusion Complexes
No full textThis paper reports a new packing type of α-cyclodextrin inclusion complexes, obtained here with succinic acid under low-temperature crystallization conditions. The structure of the 1:1 complex is characterized by heavy disorder of the guest, the solvent, and part of the host. The crystal packing belongs to the known channel-type structure; the basic structural unit is composed of cyclodextrin trimers, as opposed to the known isolated molecular or dimeric constructs, packed along the c-axis. Each trimer is made of crystallographically independent molecules assembled in a stacked vase-like cluster. A multi-temperature single-crystal X-ray diffraction analysis reveals the presence of dynamic disorder
Structural Behavior of Long-Chain Imidazolium-Based Ionic Liquid [C(10)mim]Cl-Water Mixtures
No full textThe structural behavior a long-chain imidazolium-based ionic liquid [C(10)mim]Cl-water mixtures has been HP investigated in detail by low-teruperature arid high-pressure crystallization methods, and the solid forms have been fully characterized by single-crystal X-ray diffraction. Form I, a monohydrate, crystallizes from solutions containing 6-8% (w/w) water; its structure exhibits bilayers, in which the cations alternate from layer to layer to create hydrophobic and hydrophilic regions. Form II, which is a Z' > 1 structure, incorporates a variable amount of water content (from pseudo-hemihydrate to pseudo-monohydrate) depending on the sample treatment and environment; this form crystallizes from solutions containing 80% (w/w) water. This structure is closely related -to that of-form I. While homeotypic and isotypic structures of forms I and II have been previously reported, form III represents, to the best of our knowledge, the only example of a highly hydrated long-chain imidazolium-based ionic liquid isolated in the solid state. The formation of mesophases in the title compound has also been investigated by polarized optical microscopy, and the results were correlated with previous liquid-crystal Studies on related compounds.DFG (Emmy Noether Grant) [FA 946/1-1
Crystal structure and packing energy calculations of (+)-6-aminopenicillanic acid
No full textThe X-ray single-crystal structure of (2S,5R,6R)-6-amino-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid, commonly known as (+)-6-aminopenicillanic acid (C8H12N2O3S) and a precursor of a variety of semi-synthetic penicillins, has been determined from synchrotron data at 150K. The structure represents an ordered zwitterion and the crystals are nonmerohedrally twinned. The crystal structure is composed of a three-dimensional network built by three charge-assisted hydrogen bonds between the ammonium and carboxylate groups. The complementary analysis of the crystal packing by the PIXEL method brings to light the nature and ranking of the energetically most stabilizing intermolecular interaction energies. In accordance with the zwitterionic nature of the structure, PIXEL lattice energy calculations confirm the predominance of the Coulombic term (-379.1kJmol-1) ahead of the polarization (-141.4kJmol-1), dispersion (-133.7kJmol-1) and repulsion (266.3kJmol-1) contributions
A high-pressure polymorph of propionamide from in situ high-pressure crystallisation from solution
No full textThe structure of a high-pressure polymorph of propionamide is reported from synchrotron single-crystal X-ray diffraction data. The polymorph was obtained by in situ high-pressure crystallisation from solution in a diamond-anvil cell at 0.9 GPa; its structure is 23% denser than that of the ambient-pressure polymorph at STP. PIXEL lattice and dimer energies calculations indicate that the ambient-and high-pressure polymorphs are energetically competitive. Together with acetamide and formamide, this is the third high-pressure polymorph of an aliphatic amide crystallising as a Z'=2 structure; the H-bonded network is however significantly different from the ones reported for the other two compounds. This study highlights the power of in situ high-pressure crystallisation techniques for accessing novel polymorphic forms of molecular compounds
On the temperature dependence of H-U iso in the riding hydrogen model
No full textThe temperature dependence of H-Uiso in N-acetyl-l-4-hydroxyproline monohydrate
is investigated. Imposing a constant temperature-independent multiplier
of 1.2 or 1.5 for the riding hydrogen model is found to be inaccurate, and
severely underestimates H-Uiso below 100 K. Neutron diffraction data at
temperatures of 9, 150, 200 and 250 K provide benchmark results for this study.
X-ray diffraction data to high resolution, collected at temperatures of 9, 30, 50,
75, 100, 150, 200 and 250 K (synchrotron and home source), reproduce neutron
results only when evaluated by aspherical-atom refinement models, since these
take into account bonding and lone-pair electron density; both invariom and
Hirshfeld-atom refinement models enable a more precise determination of the
magnitude of H-atom displacements than independent-atom model refinements.
Experimental efforts are complemented by computing displacement parameters
following the TLS+ONIOM approach. A satisfactory agreement between all
approaches is found
Pinning down the solid-state polymorphism of the ionic liquid [bmim][PF<sub>6</sub>]
No full textThe solid-state polymorphism of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF6], has been investigated via low-temperature and high-pressure crystallisation experiments. The samples have been characterised by single-crystal X-ray diffraction, optical microscopy and Raman spectroscopy. The solid-state phase behaviour of the compound is confirmed and clarified with respect to previous phase diagrams. The structures of the previously reported gamma-form, which essentially exhibits a G'T cation conformation, as well as those of the elusive beta- and alpha-forms, are reported. Crystals of the beta-phase are twinned and the structure is heavily disordered; the cation conformation in this form is predominantly TT, though significant contributions from other less frequently encountered conformers are also observed at low temperature and high pressure. The cation conformation in the alpha-form is GT; the presence of the G'T conformer at 193 K in this phase can be eliminated on cooling to 100 K. Whilst X-ray structural data are overall in good agreement with previous interpretations based on Raman and NMR studies, they also reveal a more subtle interplay of intermolecular interactions, which give rise to a wider range of conformers than previously considered.</p
Redetermination and invariom refinement of 1-cyclopropyl-6-fluoro-4-oxo-7-(piperazin-4-ium-1-yl)-1,4-dihydroquinoline-3-carboxylate hexahydrate at 120 K
No full textThe structure of the title compound, C17H18FN3O3·6H2O, has been redetermined at 120 K. An invariom refinement, a structural refinement using aspherical scattering factors from theoretically predicted multipole population parameters, yields accurate geometry and anisotropic displacement parameters, including hydrogen-bonding parameters. All potential hydrogen-bond donors and acceptors are involved in hydrogen bonding, forming an intricate three-dimensional network of N—H...O and O—H...O bonds
‐Butylamine System
No full textIn situ high-pressure crystallization and diffraction techniques have been applied to obtain two very structurally distinct semi-clathrates of the tert-butylamine-water system with hydration numbers 5.65 and 5.8, respectively, thereby considerably reducing a notable hydration gap between the monohydrate and the 71/4 -hydrate that results when crystallization space is explored by temperature alone. Both structures can be considered as an intriguing solid-state example of hydrophobic hydration, in which the water network creates wide tert-butylamine-filled channels stabilized by cross-linking hydrogen bonds. The existence of interconnected channels might also add low hydration structures to a list of potential targets for hydrogen storage. A detailed analysis of the topology of host water and host-guest interactions is reported and extended to those of other hydrates of the compound. This analysis offers new insight into properties of the tert-butylamine-water system and provides some clues as to the occurrence of the sizable number of hydrates of this compound.DFG [FA 964/1-1
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