π-hole interactions at work: crystal engineering with nitro-derivatives

In this manuscript, we report the design, synthesis and X-ray characterization of nitrodiene derivatives that present crucial pi-hole interactions involving the nitro group as a pi-hole donor. The solid state structures of 1,4-dinitro-1,3-butadiene (1), its co-crystal 1 . Diox, and homologous 1,4-dinitro-1,3-pentadiene (2) and 2,4dinitro-2,4-hexadiene (3) feature competition of lone pair-pi-hole interactions with common weak CH. O bonding and gradually increased role of the NO2..NO2 interactions. Regular evolution of the supramolecular patterns (1 to 3) results in generation of an unprecedented 3D non-covalent framework in 3 that is controlled exclusively by short pi-hole contacts (O..N = 2.9615.18), 3.1304(18) angstrom). These findings complement the results of high level ab initio calculations (MP2/def2-TZVP) and unite theory and experiment, thus supporting the functional relevance of this novel pi-hole interaction.