A cocrystal of L-ascorbic acid with picolinic acid: the role of O—H...O, N—H...O and C—H...O hydrogen bonds and L-ascorbic acid conformation in structure stabilization

A new 1:1 cocrystal (L-Asc–Pic) of L-ascorbic acid (vitamin C) with picolinic acid was prepared as a powder and as single crystals. The crystal structure was solved and refined from single-crystal X-ray diffraction (SCXRD) data collected at 293 (2) and 100 (2) K. The samples of the L-Asc–Pic cocrystal were characterized by elemental (HCNS) analysis and titrimetric methods, TG/DTG/DSC, and IR and Raman spectroscopy. The asymmetric unit comprises a picolinic acid zwitterion and an L-ascorbic acid molecule. The stabilization energy of intermolecular interactions involving hydrogen bonds, the vibrational spectrum and the energies of the frontier molecular orbitals were calculated using the GAUSSIAN09 and the CrystalExplorer17 programs. The charge distribution on the atoms of the L-Asc–Pic cocrystal, L-ascorbic acid itself and its 12 known cocrystals (structures from Version 5.40 of the Cambridge Structural Database) were calculated by the methods of Mulliken, Voronoi and Hirshfeld charge analyses (ADF) at the bp86/TZ2P+ level of theory. The total effective charges and conformations of the L-ascorbic acid molecules in the new and previously reported cocrystals were compared with those of the two symmetry-independent molecules in the crystals of L-ascorbic acid. A correlation between molecular conformation and its effective charge is discussed.

Newest models and calculation schemes for quantitative analysis of physical properties of polymers

New models and calculation schemes have been developed for the quantitative analysis of a number of physical properties of polymers — glass transition temperature, flow temperature of polymer nanocomposites, thermal conductivity, boiling point of polymer solutions, water absorption and water permeability of polymers and nanocomposites, strength, viscosity, storage and losses moduli, refractive index and dielectric constant. All calculation schemes are based on the structure of linear and cross-linked polymers; their degree of crystallinity, free volume, the effect of temperature, the composition of copolymers and homogeneous mixtures of polymers, the concentration of nanoparticles, their shape, size distribution, orientation angles, the structure of polar groups grafted to the surface of nanoparticles, the energy of intermolecular interactions are taken into account. All computational schemes are computerized and allow calculations to be carried out automatically after the introduction of the structure of a repeating unit of polymer unit into the computer, as well as the shape and size of nanofillers.

(E)-7-[(4-Nitrophenyl)diazenyl]-3a-(p-tolyl)-2,3,3a,4-tetrahydro-1H-benzo[d]pyrrolo[1,2-a]imidazol-1-one 0.58-dimethyl sulfoxide 0.42-acetonitrile solvate: crystal structure, Hirshfeld analysis and DFT estimation of the energy of intermolecular interactions

In the crystal structure of the title compound, C23H19N5O3·0.58C2H6OS·0.42C2H3N, prepared by the azo coupling of the 4-nitrophenyldiazonium salt with 3a-(p-tolyl)-2,3,3a,4-tetrahydro-1H-benzo[d]pyrrolo[1,2-a]imidazol-1-one, the azo molecules are linked by N—H...O hydrogen bonds into chains along thea-axis direction, and by the π–π interaction into [101] chains. The dimethyl sulfoxide and acetonitrile solvent molecules occupy the same positions, with populations of 0.585 (3) and 0.415 (3), respectively. These molecules take part in C—H...O(N) and C—H...π contacts. The energy of the π–π interactions was estimated using DFT calculations. The Hirshfeld molecular surface analysis revealed the positions of the most important intermolecular contacts, such as hydrogen bonds and π–π interactions.