A comprehensive study on the intermolecular interactions and energy frameworks exist in crystal structures of Form-I, Form-II and Form-III polymorphs of Ethyl maltol

Abstract

The present study serves as a comprehensive investigation into the molecular crystal structures of three polymorphic forms of ethyl maltol. Crystal structures of the polymorphs grown via slow evaporation and quench cooling crystallization processes were determined through single crystal X-ray diffraction (SCXRD) analysis. Through the utilization of SCXRD data CIF file as an input, we explored the nature and strength of intermolecular interactions, atom pair close contacts, interaction types, 2D fingerprint plots, surface characteristics and percentage of voids present within each polymorph of ethyl maltol. The comparative analysis involves the application of advanced methods, such as Hirshfeld surface analysis and 3D-energy frameworks using Crystal Explorer 17.5. In a supramolecular organization, intermolecular interaction between the carbonyl and hydroxyl groups is a collective structural motif employed among the three polymorphs. However the three polymorphs share common structural features, but the conformations within the crystal packing of each form are different from each other. Shape Index and Curvedness surfaces reveal π stacking interactions with varying properties on differing sides of the molecular moieties between the polymorph. Fingerprint analysis emphasizes that (H…H) is the predominant interaction whereas (O…H) and (H…O) interactions contribute more towards the generation of H-bond interactions in the structure of ethyl maltol polymorphs. The crystal structures of all the three ethyl maltol polymorphs stabilized by various intermolecular contacts within the Hirshfeld surface area was comparable. The interaction energy and the 3D-energy frameworks offer a visualization of the crystal packing topology, enhancing our understanding of the three-dimensional arrangement of molecules and their structural stability. The resulting overall average total energy values for Form-I, Form-II and Form-III polymorphs of ethyl maltol are -56.3 kJ /mol, -74 kJ /mol and -80.45 kJ /mol respectively which reveals that all the three polymorphs show a significant difference in their total energies and reveals further that Form-III polymorph of ethyl maltol is the most stable one while Form-I is the least stable and Form-II is metastable relatively. Moreover, the dispersion energy framework is predominant over the electrostatic energy framework. The void analysis reveals the percentage of volume occupied by the voids present in the unit cell of Form-I, Form-II, and Form-III polymorphs of ethyl maltol are found to be 7.20%, 6.55 %, and 9.43% respectively.