a The percentage values in parentheses give the contribution to the total attractive interactions ΔEelstat + ΔEorb.b The percentage values in parentheses give the contribution to the total orbital interactions ΔEorb.
S2N2 shows four bond critical points (BCPs) for each of the four S‒N bonds and a ring critical point (RCP) at the center (Figure 3a). The BCPs are relatively close to S-atoms, indicating bond polarization. The electron density\(\rho\left(r\right)\) and the Laplacian of the electron density\(\nabla^{2}(r)\) at the BCPs indicate the accumulation of electrons and thus a covalent nature of the bonds (Table 4). The negative total energy densityH(r) at the BCP also supports covalent nature.[64] A high ε value for S‒N bonds also indicates multiple bond character due to the presence of π-delocalization. Likewise, a substantial value of ρ(r) and\(\nabla^{2}(r)\) at the RCP indicates possible delocalization of electrons,[65] which can be correlated with the negative NICS(1)zz values (Table 2). Contour line diagram of the Laplacian distribution of the electron density\(\nabla^{2}(r)\) of the S2N2is also shown in figure 3a. Solid lines represent the areas of electronic charge concentration, while dashed lines show areas of charge depletion. The shape of the Laplacian distribution clearly shows that N atoms of the S2N2 ring have an area of charge concentration and S atoms of theS2N2 ring have an area of charge depletion along the extension of the S‒N covalent bonds.