Exploring contribution of intermolecular interactions in supramolecular layered assembly of naphthyridine co-crystals: Insights from Hirshfeld surface analysis of their crystalline states

Co-crystals of 1a and 1b have been prepared by slow evaporation of the solutions of mixtures of 2,7-dimethyl-1,8-naphthyridine (1), urea (a) and thiourea (b). The structures of the complexes are determined by the single crystal X-ray diffraction and a detailed investigation of the crystal packing and classification of intermolecular interactions is presented by means of Hirshfeld surface analysis which is of considerable current interest in crystal engineering. The X-ray study reveals that the co-crystal formers are envisioned to produce N-H center dot center dot center dot N hydrogen bond as well as N-H center dot center dot center dot O/N-H center dot center dot center dot S pair-wise hydrogen bonds and also the weaker aromatic pi center dot center dot center dot pi interactions which cooperatively take part in the crystal packing. The recurring feature of the self-assembly in the compounds is the appearance of the molecular ribbon through multiple hydrogen bonding which are further stacked into molecular layers by pi center dot center dot center dot pi stacking interactions. Hirshfeld surface analysis for visually analyzing intermolecular interactions in crystal structures employing molecular surface contours and 2D Fingerprint plots have been used to examine molecular shapes. Crystal structure analysis supported with the Hirshfeld surface and fingerprint plots enabled the identification of the significant intermolecular interactions. (c) 2013 Elsevier B.V. All rights reserved.