MP2, DFT and DFT-D study of the dimers of diazanaphthalenes: a comparative study of their structures, stabilisation and binding energies

Diazanaphthalenes (DAPs) are a broad class of N-heteroaromatic compounds with several technological and biological applications. Some of these applications are attributed to the ability of DAP molecules to form associated dimers through non-covalent interactions. A study of the types and strength of the interactions involved is crucial for understanding the preferred geometries and energetics of the dimers. In this study, the dimers of five DAPs are investigated by means of Moller-Plesset second order perturbation theory, hybrid meta-GGA [density functional theory methods (DFT): DFT/MPWB1K, DFT/M05-2X and DFT/M06-2X] and DFT dispersion-corrected (DFT-D/omega B97XD) methods to elucidate their dimers' preferred geometries, relative energies and nature of the interactions between monomer units. The results indicate that the monomer units of the dimers are held by either intermolecular hydrogen bonds or pi center dot center dot center dot pi stacking interactions, and that the preferred dimers are those in which the monomer units interact through pi center dot center dot center dot pi stacking interactions. A comparison across structures suggests that the position of the N atom in the ring has significant role in determining the relative energy and binding strength of the dimers. A comparison among the different methods utilised for the study indicates that DFT/M06-2X method provides binding energies that are close to those of DFT-CCSD(T) correction scheme and could therefore be considered as the best method for describing the binding properties of DAP dimers.