Competition between σ-hole pnicogen bond and π-hole tetrel bond in complexes of CF2=CFZH2 (Z = P, As, and Sb)
A computational study of the complexes formed by F2C=CFZH2 (Z = P, As, and Sb) and F2C=CFPF2 with two Lewis bases (NH3 and NMe3) has been carried out. In general, two minima complexes are found, one with a σ-hole pnicogen bond and the other one with a π-hole tetrel bond in most complexes but two σ-hole pnicogen bonded complexes are obtained for F2C=CFZH2 and NH3. They have similar stability though F2C=CFSbH2 engages in a much stronger σ-hole pnicogen bond with NMe3. The –PF2 substitution makes the π-hole on the terminal carbon form a tetrel bond with NH3. A heavier –ZH2 group engages in a stronger σ-hole pnicogen bond but results in a weaker π-hole tetrel bond. Other than electrostatic interaction, the stability of both complexes is attributed to the charge transfer from the N lone pair into the C–Z/H–Z anti-bonding orbital in the pnicogen bond and the C=C anti-bonding orbital in the tetrel bond.
The σ-hole pnicogen bonded and π-hole tetrel bonded complexes between F2C=CFZH2 (Z = P, As, and Sb) and two Lewis bases (NH3 and NMe3) have been compared. The results indicate that both interactions can compete, dependent on the nature of the N base.