Structural Elucidation of NO Clusters at Low Temperatures: Exemplary Framework Stabilized by π-Hole-Driven N···O and N···N Pnicogen Bonding Interactions.

NO is a classic prototype, in which central nitrogen is sufficiently electropositive with a positive potential of 20 kcal mol in magnitude to qualify it as a possible pnicogen. This was applied to a test with NO clusters using calculations in association with various molecular topographic tools. The structure of the energetically dominant and NO dimer was in favor of a perpendicular geometry, where the central nitrogen atom of the NO submolecule assumed a near 90° angle with the adjacent N═O and/or N═N moiety, which provides the affirmation of central nitrogen as a possible π-hole-driven pnicogen. The terminal nitrogen and oxygen atoms of NO continue to act as conventional electron donors (Lewis bases) with a negative potential. Overall, predominant π-hole-driven N···O and N···N pnicogen bonding interactions were observed to stabilize NO clusters. Furthermore, NO clusters (dimers and trimers) were synthesized at low temperatures in an Ar matrix using molecular beam (effusive and supersonic expansion) experiments. The geometries of these clusters were characterized by probing infrared spectroscopy with corroboration from computational methods. In addition to our previously investigated nitromethane and nitrobenzene systems, NO also makes it to a pnicogen bonder's club with the central nitrogen as a π-hole-driven pnicogen.