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

Similar to σ-hole interactions, the π-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⋯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 π-hole interaction energy becomes greater as the trend goes from 1⋯XH₃ to 4⋯XH₃. These π-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 π-hole complexes, with the contrasting phenomena of decreasing electronic density in the π-hole region and increasing electric density outside the X atom of XH₃ (X = N, P, As). Graphical abstract Computed density difference plots for the complexes 3⋯NH ₃ (a ₁), 3⋯PH ₃ (b ₁), 3⋯AsH ₃ (c ₁) and electron density shifts for the complexes 3⋯NH ₃ (a ₂), 3⋯PH ₃ (b ₂),3⋯AsH ₃ (c ₂) on the 0.001 a.u. contour.