Systematic Exploration of Structural Topologies in Hydrogen-Bonded Supramolecular Assemblies of Citric Acid with Different Heterocyclic Compounds

Hydrogen-bonded supramolecular assemblies of citric acid, CA, with some heterocyclic compounds (N-donor and N-oxide)-acridine (acr), phenazine (phenz), 1,10-phenanthroline (110phen), 1,7-phenanthroline (17phen), 4,7-phenanthroline (47phen), 1,4-diazabicyclo[2.2.2]octane (dabco), and 4,4'-bipyridyl-N,N'-dioxide (bpydo)-have been reported. Among these, only the N-donors phenz and N-oxide (bpydo) form neutral co-crystals, while the others form salts owing to the deprotonation of -COOH. Thus, depending on the nature of the aggregate (salt/co-crystal), recognition between the co-formers is established through O-H···N/N⁺-H···O/N⁺H···O^-heteromeric hydrogen bonding. Additionally, CA molecules establish homomeric interactions mediated by O-H···O hydrogen bonds. Moreover, CA forms a cyclic network with the co-formers or on its own, with a noteworthy feature of formation of host-guest networks in the assemblies with acr and phenz (solvated). In the assembly of acr, the CA molecules form a host network and captivate acr molecules as guest species, while in the case of phenz assembly, both the co-formers together encapsulate the solvent in the channels. However, the observed cyclic networks in the other structures form three-dimensional topologies in the form of ladders, a sandwich, lamellar layers, and interpenetrated networks. The structural features of the ensembles are evaluated unequivocally by the single-crystal X-ray diffraction method, while the homogeneity and phase purity are evaluated by using the powder X-ray diffraction method and differential scanning calorimetry. Further, conformational analysis of CA molecules reveals three types of conformations-T-shape (type I), syn-anti (type II), and syn (type III) as also observed in the literature for other CA co-crystals. In addition, the strength of the intermolecular interactions is quantified by performing Hirshfeld analysis.

Electrostatic properties of the pyrimethamine–2,4-dihydroxybenzoic acid cocrystal in methanol studied using transferred electron-density parameters

The crystal structure of the cocrystal salt form of the antimalarial drug pyrimethamine with 2,4-dihydroxybenzoic acid in methanol [systematic name: 2,4-diamino-5-(4-chlorophenyl)-6-ethylpyrimidin-1-ium 2,4-dihydroxybenzoate methanol monosolvate, C12H14ClN4 +·C7H5O4 −·CH3OH] has been studied using X-ray diffraction data collected at room temperature. The crystal structure was refined using the classical Independent Atom Model (IAM) and the Multipolar Atom Model by transferring electron-density parameters from the ELMAM2 database. The Cl atom was refined anharmonically. The results of both refinement methods have been compared. The intermolecular interactions have been characterized on the basis of Hirshfeld surface analysis and topological analysis using Bader's theory of Atoms in Molecules. The results show that the molecular assembly is built primarily on the basis of charge transfer between 2,4-dihydroxybenzoic acid and pyrimethamine, which results in strong intermolecular hydrogen bonds. This fact is further validated by the calculation of the electrostatic potential based on transferred electron-density parameters.

Cocrystals of the antibiotic trimethoprim with glutarimide and 3,3-dimethylglutarimide held together by three hydrogen bonds

The antibiotic trimethoprim [5-(3,4,5-trimethoxybenzyl)pyrimidine-2,4-diamine] was cocrystallized with glutarimide (piperidine-2,6-dione) and its 3,3-dimethyl derivative (4,4-dimethylpiperidine-2,6-dione). The cocrystals, viz. trimethoprim-glutarimide (1/1), C14H18N4O3·C5H7NO2, (I), and trimethoprim-3,3-dimethylglutarimide (1/1), C14H18N4O3·C7H11NO2, (II), are held together by three neighbouring hydrogen bonds (one central N-H...N and two N-H...O) between the pyrimidine ring of trimethoprim and the imide group of glutarimide, with an ADA/DAD pattern (A = acceptor and D = donor). These heterodimers resemble two known cocrystals of trimethoprim with barbituric acid and its 5,5-diethyl derivative. Trimethoprim shows a conformation in which the planes of the pyrimidine and benzene rings are approximately perpendicular to one another. In its glutarimide coformer, five of the six ring atoms lie in a common plane; the C atom opposite the N atom deviates by about 0.6 Å. The crystal packing of each of the two cocrystals is characterized by an extended network of hydrogen bonds and contains centrosymmetrically related trimethoprim homodimers formed by a pair of N-H...N hydrogen bonds. This structural motif occurs in five of the nine published crystal structures in which neutral trimethoprim is present.

Crystalline adducts of the Lawsone molecule (2-hydroxy-1,4-naphthaquinone): optical properties and computational modelling

Crystal-engineering techniques allow the colour of the molecule in henna dye (Lawsone) to be tuned from yellow to red.