To investigate the nature of non-covalent selenium–p interaction, the intermolecular interactions between benzene p system and R2Se (R = H, F, Cl, CH3) as well as C4H4Se (selenophene) were quantified using DFT and MP2 methods. The obtained data revealed that the strength of Se p interaction follows the order F2Se > Cl2Se > selenophene > H2Se > Me2Se. Thus the existence of electron withdrawing group on Se atom increases the strength of Se p interaction. In contrast, the calculations on F2Se C6(R0)6 (R0 = F, CH3) complexes showed that the existence of fluorine electron withdrawing atoms on benzene ring decrease the above interaction and methyl electron donating groups increase it. The second order perturbation energies as well as the global value of charge transfer calculated through NBO analysis showed that the interaction of filled p molecular orbitals of benzene or its derivatives with R2Se molecule is more important than the interaction of its empty p⁄ molecular orbitals with selenium lone pairs. The breakdown of total interaction energy DEint in the R2Se C6H6 (R = H, F, Cl, CH3), C4H4Se C6H6 and F2Se C6R0 6 (R0 = F, CH3) systems using two dispersion corrected DFT methods showed that when the R group on divalent selenium atom is an electron withdrawing substituent and R0 group on p system is an electron donating substituent, then the contribution of DEelstat and DEorb in total interaction energy is considerably larger than DEdisp and therefor DEint is relatively large. The EDA–NOCV data confirmed that the direction of main charge flow is from the benzene ring to F2Se fragment.
