Crystal engineering in all its hues in

Insights on structure and interactions of 2-amino-4-methoxy-6-methylpyrimidinium salts with 4-aminosalicylate and 5-chlorosalicylate: a combined experimental and theoretical charge–density analysis

The proton-transfer complexes 2-amino-4-methoxy-6-methylpyrimidinium (2A4M6MP) 4-aminosalicylate (4AMSA), C6H10N3O+·C7H6NO3 −, I, and 5-chlorosalicylate (5ClSA), C6H10N3O+·C7H4ClO3 −, II, were synthesized by slow evaporation and crystallized. The crystal structures of both I and II were determined by single-crystal X-ray structure analysis. The crystal structures of both salts exhibit O—H...O, N—H...O, N—H...N and C—H...O interactions in their crystals. The 4AMSA and 5ClSA anions in combination with the 2A4M6MP cations form distinct synthons, which are represented by the graph-set notations R 2 2(8), R 4 2(8) and R 2 2(8). Furthermore, the ΔpK a values were calculated and clearly demonstrate that 2A4M6MP is a good salt former when combined with carboxylic acids. Hirshfeld surface analysis was used to quantify the weak and strong interactions in the solid state, and energy framework calculations showed the stability of the hydrogen-bonding interactions. QTAIM (quantum theory of atoms in molecules) analysis revealed the nature of the chemical bonding in I and II, and the charge–density distribution in the intermolecular interactions in the crystal structures.

Salt formation, hydrogen-bonding patterns and supramolecular architectures of acridine with salicylic and hippuric acid molecules

The intermolecular interactions and salt formation of acridine with 4-aminosalicylic acid, 5-chlorosalicylic acid and hippuric acid were investigated. The salts obtained were acridin-1-ium 4-aminosalicylate (4-amino-2-hydroxybenzoate), C₁₃H₁₀N⁺·C₇H₆NO₃^- (I), acridin-1-ium 5-chlorosalicylate (5-chloro-2-hydroxybenzoate), C₁₃H₁₀N⁺·C₇H₄ClO₃^- (II), and acridin-1-ium hippurate (2-benzamidoacetate) monohydrate, C₁₃H₁₀N⁺·C₉H₈NO₃^-·H₂O (III). Acridine is involved in strong intermolecular interactions with the hydroxy group of the three acids, enabling it to form supramolecular assemblies. Hirshfeld surfaces, fingerprint plots and enrichment ratios were generated and investigated, and the intermolecular interactions were analyzed, revealing their quantitative contributions in the crystal packing of salts I, II and III. A quantum theory of atoms in molecules (QTAIM) analysis shows the charge-density distribution of the intermolecular interactions. The isosurfaces of the noncovalent interactions were studied, which allows visualization of where the hydrogen-bonding and dispersion interactions contribute within the crystal.

Increasing complexity: structural equivalence and combinatorial approaches to preparation of high order cocrystals

An algorithmic strategy to design stoichiometric quaternary and solid-solution quinary solids is described. The strategy involves recognition of structural inequivalences to generate ternary and quaternary cocrystals which can then be extended to five-component solid solutions through matching of suitable interactions.