Figure 2 . Structure of the pnicogen bonding binary complex (R-Ph-CN…PO2F).
The geometry and the complexation energy of the considered binary systems are given in Table 2. The nonlinear C-N…P structure is due to the fact that the most positive MEP of the π hole of PO2F locates at the P-F bond closing to the P atom. Furthermore, upon formation of the π-hole pnicogen bond, the PO2F molecule deviates from the original planar structures, which is described by the following deformation energy. The pnicogen bond distance r(N…P) (the distance between N and P atoms) of Ph-CN…PO2F complex is 1.924 Å, much smaller than the sum of van der Walls (vdW) radii of N and P atoms (3.35Å)[50], indicting the existence of intermolecular interactions in the studied systems. When the para -H atom in Ph-CN is replaced by different substituents, it is found that the distance between N and P decreases for the-CH3 and -NH2 complexes, while the distance becomes larger for the halogen atom and CN group. As seen in Table 2, the pnicogen-bond length r(N…P) decease following the order of CN>Br≈Cl>F>H>CH3>NH2, which is consistent with the order of the Vs, min on the N atom of isolated substituted R-Ph-CN observed in the MEP analysis.
Table 2. The geometric and energetic aspects of the binary complexes (energy unit: kcal/mol).