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

Hydrogen-bonded supramolecular assemblies of citric acid, , with some heterocyclic compounds (-donor and -oxide)-acridine (), phenazine (), 1,10-phenanthroline (), 1,7-phenanthroline (), 4,7-phenanthroline (), 1,4-diazabicyclo[2.2.2]octane (), and 4,4'-bipyridyl-,'-dioxide ()-have been reported. Among these, only the -donors and -oxide () 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/NH···O hydrogen bonding. Additionally, molecules establish interactions mediated by O-H···O hydrogen bonds. Moreover, 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 and (solvated). In the assembly of , the molecules form a host network and captivate molecules as guest species, while in the case of 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 molecules reveals three types of conformations-T-shape (type I), (type II), and (type III) as also observed in the literature for other co-crystals. In addition, the strength of the intermolecular interactions is quantified by performing Hirshfeld analysis.