Halogen bonding interactions of sym-triiodotrifluorobenzene with halide anions:: A combined structural and theoretical study

Cocrystallization of 1,3,5-trifluoro-2,4,6-triiodobenzene (sym-TFTIB) with (Bu4NX)-Bu-n or Ph4PX (X = Cl-, Br-) afforded the 1:1 complex salts formulated as (sym-TFTIB)((Bu4NCl)-Bu-n), (sym-TFTIB)((Bu4NBr)-Bu-n), (sym-TFTIB)(Ph4PCl)(H2O)(0.5) or (sym-TFTIB)(Ph4PBr). In all four salts, each halide anion is halogen bonded to three iodine atoms from three different sym-TFTIB molecules, affording a recurrent polymeric two-dimensional anionic network, characterized by short I center dot center dot center dot X distances and linear C-I center dot center dot center dot X but acute I center dot center dot center dot X-center dot center dot center dot I angles (X- = Cl-, Br-). Topological analysis of the electron localization function (ELF) shows a perfect match between the iodine valence shell electrons, with a belt-shape arrangement around the C-I axis, and the spherical halide anions. The lack of covalent character for the halogen bond allows the simultaneous participation of one X- anion in three halogen bonds.