Insight into the pseudo π-hole interactions in the M3H6(NCF)n (M = C, Si, Ge, Sn, Pb; n = 1, 2, 3) complexes

For cyclopropane and its derivatives M3H6 (M = C, Si, Ge, Sn, Pb), "pseudo π-hole" regions above and below the M-M-M three-membered ring have been discovered, and pseudo π-hole interactions between M3H6 and F-CN have been designed and investigated by MP2/aug-cc-pVTZ and MP2/aug-cc-pVTZ-pp calculations. To investigate the enhancing effects of FN halogen bonds on the pseudo π-hole interactions, the termolecular and tetramolecular complexes M3H6(NCF)n (n = 2, 3) were constructed. Energy decomposition analysis shows that the dispersion term contributes the most among the three attractive components in the C3H6(NCF)n (n = 1, 2, 3) complexes while in the Si3H6(NCF)n and Ge3H6(NCF)n complexes, the electrostatic term has the largest contribution. The electrostatic and polarization energies have more effect than the dispersion energy for the enhancement of the FN halogen bond on the pseudo π-hole interactions. With the increase in the number of NCF units from 1 to 3, the VS,min values outside the nitrogen atom of NCF become increasingly negative, the electric field of the lone pair of nitrogen becomes greater and causes a further increase of electron density outside the nitrogen atom and a further decrease of electron density outside the pseudo π-hole region, resulting in a stronger pseudo π-hole interaction.