LAUSR

The effects of chlorine substituents (Cl substituents) on the structural and electronic properties of lichexanthones (LXs) such as aromaticity of rings, the intramolecular interactions and the complexation of LXs with Mg2+ and NH3 (the ionic and halogen bond interactions) have been investigated by the quantum mechanical calculations at the M06-2X/6-311++G(d,p) level of theory. The effects of Cl substituents on the intramolecular H-bond interactions strongly depend on their positions on the ring. The Cl substituents increase the E2 values of nX → π*CC interactions, obtained from the natural bond orbital analysis, reduce the electron densities on the center of the substituted ring, ρRCP in the results of atoms in molecules analysis, and decrease the aromaticity of the rings with respect to the aromatic fluctuation index. The stabilities of compounds depend on the aromaticity of rings, the O···H-bond strength, and especially the Cl···H interaction. Also, the effects of substituents on the local minimum values of electrostatic potential around the O atoms (Vmin) and therefore the binding energies of [LX···Mg]2+ and [LX···Mg·4H2O]2+ complexes strongly depend on the positions of the substituents. The aromaticity of rings A and C decrease and that of B increases after complexation with the Mg2+ ion. The electronic effects (and in some cases the steric effects) play a special role in the formation and stability of LX···NH3 complexes. The stabilities of the LX···NH3 complexes increase by increasing the natural charges and the local maximum electrostatic potential (Vmax−Cl) calculated, respectively, on and around the Cl atoms, and the ρCl−N values calculated at the Cl···N BCPs.