Weak Interaction Based Interpretation of Crystal Packing Characteristics of Aromatic Rings Accumulating Molecules: Hirshfeld Surface Analyses Reinforced X-ray Crystal Study on 1,8-Dibenzoyl-7-Ethoxynaphthalen-2-ol and Its 2-Ethoxylated Homologue

Abstract

The molecular environments in the crystal of two dibenzoylnaphthalene derivatives, having similar molecular formulas with a difference of only one substituent, that is, a 2-hydroxy group and 2-ethoxy group, were comparatively investigated with respect to the types of weak interactions, using an X-ray crystal structural study reinforced by Hirshfeld surface analysis and two-dimensional plotting of the normalised interatomic distance crossing the molecular surface. The general X-ray crystal structural analysis determined effective non-covalent bonding intra/intermolecular interactions to be the governing interactions for molecular packing based short interatomic distances. The minute spatial structure around respective interactions demonstrates the characteristics of non-covalent bonding interatomic interactions. The general X-ray crystal structural analysis further revealed the relationship between the entire crystalline symmetricity and the fashion of the interactions. Hirshfeld surface analysis revealed the location of the short contacts on the molecular surface. Two-dimensional plotting exhibited the contribution of the interacting atomic pairs covering the molecular surfaces as the geometrical distribution of the effective intermolecular non-covalent bonding interactions. The differences in the determined packing features and proximity of the two compounds were rationally interpreted according to the strength categorisation of the non-covalent bonding interactions especially in relation to the proportional/disproportional distribution of the molecular contact index. The comparison illustrated that the superior intermolecular interaction concentrates on the short interatomic distances and strain at the specified region of the molecular aggregate, resulting in adequate flexibility of the extroverted sides to achieve highly symmetrical interactions.

Graphical Abstract

Ethoxy–hydroxy diaroylnaphthalene compound forms cyclic classical hydrogen bond-based dimeric aggregate bearing four C–H‧‧‧O non-classical hydrogen bonds in the core region and four effective π‧‧‧π stackings around the extroverted zone, whereas ethoxy–ethoxy homologous compound shows π‧‧‧π stacking based dimeric aggregate having four C–H‧‧‧O non-classical hydrogen bonds around the extroverted zone.