3 Results and Discussion
3.1 Substitution Effect on the pnicogen
bond
3.1.1 MEPs analysis
To better understood the structure of the complexes, the MEP analysis
was performed for the selected molecules. The MEP maps of
PO2F and Ph-CN are illustrated in Figure 1, in which the
most positive regions are designated by a red color. Due to the similar
profile as Ph-CN, the MEP maps of a series of substituted benzonitrile
R-Ph-CN (R=F, Cl, Br, CH3, NH2, CN) we
studied are all given in Figure S1 of Supporting Information. The values
of the most positive and negative electrostatic potential
(Vmax and Vmin) in the isolated monomers
are listed in Table 1. It is observed that there is a π-hole (red
region) on the outermost portion of the P surface, which are
perpendicular to the molecular framework. The π-hole value
(Vmax) is 61.59 kcal/mol for the P atom in
PO2F monomer, and this enables PO2F to
form a
π-hole
pnicogen bond as a strong Lewis acid with R-Ph-CN compounds. As for the
isolated R-Ph-CN molecules, the electron-donating group shifts the
electron density towards the CN side, and this results in the potential
associated with the N atom becomes more negative. The absolute value of
Vmin on the N atom increases with respect to substituent
R in the order of
CN<Br≈Cl<F<H<CH3≈NH2.
Here, the power of electron-withdrawn of the halogen substituents is a
little different from the previous report for small molecules[49].