Noncovalent Interactions Involving lodofluorobenzenes: The Interplay of Halogen Bonding and Weak Ip(O)center dot center dot center dot pi-Hole(arene) Interactions

Fluorinated iodoarenes such as 1,4-diiodotetrafluorobenzene (1,4-FIB) and 1,3,5-triiodotrifluorobenzene (1,3,5-FIB) were cocrystallized with the nitrosoguanidinate-nickel(II) species[Ni{NH=C(NRR')NN(O)}2](RR' = Me-2 1, RR' = MePh 2, RR' = (CH2)(5) 3) and structures of three adducts were studied by X-ray crystallography. The Hirshfeld surface analysis for the X-ray structures of 1.(1,4-FIB), 2.2(1,3,5-FIB), and 3.2(1,4-FIB) revealed that crystal packing is determined primarily by intermolecular contacts involving hydrogen and halogen atoms. In addition, FIBs are linked to the 0 atom of the nitroso-group via pi-hole of the arene cores thus representing an unreported noncovalent bonding pattern for iodofluorobenzenes; it belongs to lone pair(O)-pi hole interactions, lp(O)-pi h. Results of DFT calculations followed by QTAIM analysis at the M06/DZP-DICH level of theory revealed that estimated energies of the lp(O) Rh interactions are 1.3-2.2 kcal/mol (in experimental X-ray geometries of model supramolecular adducts) or 0.9-2.4 kcal/mol (in equilibrium optimized geometries of model supramolecular adducts). The geometry optimization procedure for model adducts does not change significantly the structural motifs of these systems indicating that lp(O)-pi h contacts are not determined exclusively by crystal packing effects, but also exist in the isolated gas phase form. Our processing of the CCDC database and the theoretical calculations for TAXZAW01, featuring the shortest O center dot center dot center dot arene distance, revealed five additional structures with overlooked lp(O)-pi h contacts involving iodofluoroarene cores.