Strong halogen bonding of 1,2-diiodoperfluoroethane and 1,6-diiodoperfluorohexane with halide anions revealed by UV-Vis, FT-IR, NMR spectroscopes and crystallography

The spectroscopic methods UV-Vis absorption, FT-IR and C-13 and F-19 NMR demonstrate that 1,2-diiodoperfluoroethane (DIPFE) and 1,6-diiodoperfluorohexane (DIPFH) display strong halogen bonding with halide anions. A 1 : 1 stoichiometry of DIPFE or DIPFH with halide anion is confirmed, and the bonding constants and molar extinction coefficients are obtained. With the same halide, DIPFH possesses greater bonding constants and molar extinction coefficients than DIPFE. Furthermore, the bonding constants present in this article are far greater than those of all halogen bonding complexes reported. Interestingly, the FT-IR spectrum indicates that halogen bonding promotes a conversion from gauche to trans conformer of DIPFE. The X-ray data further confirm a 1 : 1 stoichiometry and all DIPFE and DIPFH exist in trans conformers in cocrystals which were assembled with halide anions. As potential persistent organic pollutions, iodinated perfluoroalkanes have been paid much attention. The present study will benefit current research of their separation and recognition in environmental samples.