On the Importance of Nonbonding Donor-Acceptor Interactions Involving PO₂^. Radicals: An ab Initio Study

In this study, several σ-type and π-hole bonding complexes between PO₂^. radicals and electron-rich entities have been optimized at the RI-MP2/aug-cc-pVQZ level of theory. We have used Cl^- , Br^- , I^- anions, and ethene, ethyne, HCN, HF, and H₂ O as Lewis bases. In addition, we have performed natural bond orbital (NBO) and Mulliken spin density analyses, highlighting the donor-acceptor nature of the interaction. Moreover, an interesting retro-donation from the single electron lone pair of the PO₂^. radical to the Lewis base also contributes to the stabilization of the complexes studied herein. Finally, the Bader's atoms-in-molecules (AIM) analysis of several complexes has been performed to further characterize the interactions discussed herein.