Quantitative Analysis of Intermolecular Interactions in 7-Hydroxy-4-methyl-2H-chromen-2-one and Its Hydrate

The determination of the crystal and molecular structure of organic compounds has contributed immensely towards the area of crystal engineering. This contributes towards the understanding of the molecular geometry and the different intermolecular interactions which control crystal packing. An approach which quantifies the energetics associated with the formation of different “molecular pairs” is of importance to recognize the hierarchy of intermolecular interactions present in the crystal. We intend to explore different computational tools which contribute towards the field of crystal engineering. In this regard, the crystal structure of 7-hydroxy-4-methyl-2H-chromen-2-one and its hydrate were re-determined and their crystal packing were analyzed in terms of the interaction energy of different intermolecular interactions, calculated by PIXEL method, contributing towards the stabilization of the crystal packing. The system is so chosen such that it allows the analysis of weak interactions like C–H···O, C–H···π, π···π, lp···π etc. in the presence of strong O–H···O hydrogen bonds and also allows for a systematic exploration of the effect of solvent (water in the present case) on the crystal packing. The calculation of the lattice energy reveals that the anhydrous form is 7 kcal/mol more stable than the corresponding hydrate. The major stabilization towards the crystal packing were observed to come from strong O–H···O=C hydrogen bonds (9 kcal/mol) in case of the anhydrous form while in case of its hydrate, water acts as both an acceptor and a donor of the hydrogen bonds, the interaction energy ranging from 5 to 9 kcal/mol. The weak C–H···O hydrogen bond were found to be the second highest contributor (I.E = 3.5–5.5 kcal/mol) towards the stabilization of the packing in both the crystal structures. The main differences in the crystal packing were observed in the presence of weaker interactions in their crystal packing. The weak C–H···π, O(lp)···C=O interactions were observed in the crystal packing of the anhydrous form while the π···π, O(lp)···π interactions stabilize the crystal packing in case of its hydrate. This phenomenon were further well supported by the analysis of the Hirshfeld surfaces mapped with different properties, 2D-fingerprint plots, electrostatic potential mapped on the Hirshfeld surface and electron density isosurface (calculated by ab initio calculation at DFT-D3/B97-D) at both solid state and optimized geometry.