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).