Deriving General Energy Predictors for Pnictogen Bonding

A comprehensive quantum chemical study is presented to derive energetic predictors for pnictogen (Pn) bonding interactions. We analyzed the interaction energies of the Lewis acids PnF₃ and F₂PnX, where Pn represents nitrogen through bismuth and X represents chlorine, bromine, or iodine, acting as σ-hole donors with a diverse set of up to twenty-one different nitrogen- and oxygen-based Lewis bases. All complexes were investigated at the PBE0-D3/def2-TZVP level of theory. For every complex, a topological analysis according to Bader's quantum theory of atoms in molecules (QTAIM) was performed to correlate the interaction energies with the potential energy density values at the bond critical points. We established a linear correlation with reasonable R-squared values for the coordination behavior of each pnictogen atom. Furthermore, the results demonstrate that, as the size, polarizability, and σ-hole intensity of the pnictogen atom increase, the likelihood of forming additional secondary noncovalent interactions also rises. Consequently, a clear differentiation must be made between pure pnictogen bonding and a combination of pnictogen bonding with secondary interactions. This distinction is supported by the analysis of several published crystal structures. We propose general energy predictors for the determination of pure pnictogen bond energies.