Crystal structure of 1:1 complex of barbital with 1-methylimidazole

Multicomponent Crystal of Metformin and Barbital: Design, Crystal Structure Analysis and Characterization

The formation of most multicomponent crystals relies on the interaction of hydrogen bonds between the components, so rational crystal design based on the expected hydrogen-bonded supramolecular synthons was employed to establish supramolecular compounds with desirable properties. This theory was put into practice for metformin to participate in more therapeutic fields to search for a fast and simple approach for the screening of candidate crystal co-formers. The prediction of intermolecular synthons facilitated the successful synthesis of a new multicomponent crystal of metformin (Met) and barbital (Bar) through an anion exchange reaction and cooling crystallization method. The single crystal X-ray diffraction analysis demonstrated the hydrogen bond-based ureide/ureide and guanidine/ureide synthons were responsible for the self-assembly of the primary structural motif and extended into infinite supramolecular heterocatemeric structures.

Insight into the Structure and Properties of Novel Imidazole-Based Salts of Salicylic Acid

The preparation of new active pharmaceutical ingredient (API) multicomponent crystal forms, especially co-crystals and salts, is being considered as a reliable strategy to improve API solubility and bioavailability. In this study, three novel imidazole-based salts of the poorly water-soluble salicylic acid (SA) are reported exhibiting a remarkable improvement in solubility and dissolution rate properties. All structures were solved by powder X-ray diffraction. Multiple complementary techniques were used to solve co-crystal/salt ambiguities: density functional theory calculations, Raman and ¹H/¹³C solid-state NMR spectroscopies. In all molecular salts, the crystal packing interactions are based on a common charged assisted ⁺N-H_(SA)⋯O⁻_(co-former) hydrogen bond interaction. The presence of an extra methyl group in different positions of the co-former, induced different supramolecular arrangements, yielding salts with different physicochemical properties. All salts present much higher solubility and dissolution rate than pure SA. The most promising results were obtained for the salts with imidazole and 1-methylimidazole co-formers.

Structural investigation and Hirshfeld surface analysis of three organic picrate salts

Three picrate salt crystals, namely 5-amino-6-methylquinolin-1-ium 2,4,6-trinitrophenolate (I), 3-phenyl-1H-pyrazol-2-ium 2,4,6-trinitrophenolate (II) and 1H-imidazol-3-ium 2,4,6-trinitrophenolate (III) were characterized by X-ray diffraction. Salt I crystallizes in space group of P21/c, with a=15.096(2), b=7.2864(9), c=15.248(2) Å, β=98.437(2)°, V=1659.1 Å3 and Z=4. Salt II crystallizes in monoclinic space group P21/c, with a=13.6230(9), b=6.7421(5), c=17.7508(12) Å, β=106.001(1)°, V=1567.20 Å3 and Z=4. Whereas salt III crystallizes in triclinic system, space group P1̅, with a=7.6919(10), b=7.9218(10), c=10.2230(13) Å, α=81.909(2), β=77.985(2), γ=82.629(2)°, V=600.05 Å3 and Z=2. Protons were transferred from the picric acids to their corresponding bases, forming intermolecular N+–H···O− hydrogen bonds in the three salts. Salts I and II form planes, whereas salt III forms chains via N–H···O and C–H···O hydrogen bonds as their supramolecular assembly. Planes and chains in all these salts were interconnected through π···π interaction. The intermolecular interactions in the crystal structures were quantified and were analysed using Hirshfeld surface analysis.