Insight into π-hole interactions containing the inorganic heterocyclic compounds S2N2/SN2P2

Similar to sigma-hole interactions, the pi-hole interaction has attracted much attention in recent years. According to the positive electrostatic potentials above and below the surface of inorganic heterocyclic compounds S2N2 and three SN2P2 isomers (heterocyclic compounds 1-4), and the negative electrostatic potential outside the X atom of XH3 (X = N, P, As), S2N2/SN2P2 center dot center dot center dot XH3 (X = N, P, As) complexes were constructed and optimized at the MP2/aug-cc-pVTZ level. The X atom of XH3 (X = N, P, As) is almost perpendicular to the ring of the heterocyclic compounds. The pi-hole interaction energy becomes greater as the trend goes from 1 center dot center dot center dot XH3 to 4 center dot center dot center dot XH3. These pi-hole interactions are weak and belong to "closed-shell" noncovalent interactions. According to the energy decomposition analysis, of the three attractive terms, the dispersion energy contributes more than the electrostatic energy. The polarization effect also plays an important role in the formation of pi-hole complexes, with the contrasting phenomena of decreasing electronic density in the pi-hole region and increasing electric density outside the X atom of XH3 (X = N, P, As).