Nitrogen in supramolecular chemistry: Understanding the pervasive role as acceptor of halogen, chalcogen, pnictogen and tetrel bonds

Nitrogen-centered Lewis bases are well established as nucleophiles in synthetic chemistry, as ligands in coordination chemistry and as pervasive components of hydrogen bonding in chemistry and structural biology. Their role as acceptors of halogen, chalcogen, pnictogen and tetrel bonds, collectively σ-hole interactions, is also well established experimentally, but only selectively investigated through exploration of geometric and energetic trends. Here we report a comprehensive study, in which we identify the prevalence of this class of interactions and analyze experimental geometric trends from crystallographic data. These analyses are supported by high-accuracy coupled-cluster quantum chemical calculations of interaction energies and use of symmetry-adapted perturbation theory (SAPT) to examine the underlying energetic contributions. Our focus is on comparison, across the four families of σ-hole interactions, of the behavior for Nsp3 vs Nsp2 vs Nsp hybridization at the nitrogen atom bearing the lone pair. Halogen and chalcogen bonds are more abundant than pnictogen and tetrel bonds, whereas interaction prevalence tends to be greatest for the heavier congeners in each σ-hole donor group (i.e., I, Te, Sb/Bi, Sn/Pb). The relative prevalence of tetrel bonds compared to halogen bonds increases from Nsp3 to Nsp2 to Nsp acceptors, highlighting the importance of steric demands. The heavier congeners among the σ-hole donors generally form interactions with shorter normalized interaction distances, although this is mitigated by sterics, most prominently for tetrel bonds and for Nsp3 Lewis bases. Preference for linearity with respect to the σ-hole angle and the angle at the nitrogen lone pair follow the trend Nsp3 > Nsp2 > Nsp also as a consequence of steric demands. More generally, SAPT analysis of interaction energies clearly indicates the prominent influence of sterics, through exchange repulsion, on angular preferences of all interactions. The broader implications of these comprehensive results in areas such as supramolecular, materials and medicinal chemistry are considered.