Site-selective assembly between 1,8-diiodoperfluorooctane and 4,7,8,11-tetraazahelicene driven by halogen bonding

The X-ray diffraction analysis on single crystals obtained from the self-assembly of 1,8-diiodoperfluorooctane 1 with the tetraazahelicene derivative 2 revealed a site-selective pattern of halogen bonds (XBs) in the solid state. Indeed, two non-equivalent XBs drive the formation of an indefinitely repeating pentameric (1)3 center dot(2)2 unit. Interestingly, the N...I-C bonding formation occurred selectively on the pyridazinic/cinnolinic nitrogen atoms of the tetraazahelicene unit, which were preferred over the pyridinic/quinolinic ones. On the basis of molecular electrostatic potential and molecular orbital analyses, DFT calculations predicted and explained well this site-selective XB formation, thus demonstrating to be efficient tools for the prediction of the XB site selectivity in similar polynitrogen systems.