Intermolecular Interaction Energies in Molecular Crystals of 4-Formylcoumarin Derivatives

Most of the crystallographic analysis that follows from structure determination involves interpretation of the molecular geometry and a working knowledge of a variety of intraand intermolecular interactions based purely on geometrical considerations (distance and angle cut off criteria). The missing link is to explore the energetics associated with these interactions, particularly intermolecular ones, which provide a platform for the molecules to associate with each other. In this regard, PIXEL calculations have been performed on a series of six molecules of 4-formylcoumarin derivatives. PIXEL calculations suggest the presence of different structural motifs that play significant role in the stabilization of the structure. Analysis of these motifs shows that bifurcated C-H...O and π...π stacking are the major contributors towards the stabilization of the structure. However, it is found that molecular pairs interacting via dimeric C=O...C=O interaction also make significant contribution of almost -5 kcal mol. In addition to these motifs, the role of weak C-H...X (F, Cl or Br) has also been explored in the stabilization of molecular packing.