A comparative study of X-ray structural analysis, DFT computations, and Hirshfeld surface analysis for decahydroacridine-1,8-diones

Crystal structure analysis and DFT computational calculation of two symmetrical and unsymmetrical decahydroacridine-1,8-diones (DHACs) were carried out to elucidate the effect of the aryl-substituted heterocyclic core in these compounds on the comparative bond lengths, bond, and dihedral angles. According to these findings, the central heterocyclic ring in these compounds is exhibited in the pseudo-boat conformation, in which the aryl substitution occupies the pseudo-axial position. Moreover, the fused outer rings were in the twisted half-chair conformation. The weak and strong inter- and intramolecular interactions between the suitable donor–acceptor positions (N‒H···O, C‒H···O, H‒N···H and C‒H···π of the C=C double bond) in symmetrical and enantiomeric pairs of unsymmetrical DHACs affect the orientation of the molecules in the crystal packing. The relative contributions of various intermolecular interactions in these compounds are evaluated using Hirshfeld surface analysis. The DFT calculations were performed to outline the optimized structure, molecular electrostatic potential (MEP), frontier molecular orbitals (FMOs), natural bond orbital (NBO) and to elucidate the effect of the space orientation of the attached aryl ring toward the heterocyclic ring on the total energy content of DHAC 2. Additionally, MEP analysis in DHAC 2 revealed that the negative electrostatic potential is more concentrated around the O₁-atom of the C₁=O₁ double bond than the O₂-atom of the C₁₃=O₂ double bond. The results of the NBO analysis demonstrated that in the crystal packing of compounds 1 and 2 the strongest intermolecular interaction occurs from the LP(2)O₂ to σ*(N₁–H) and LP(1)O₁ to σ*(N₁‒H), respectively.