Study of the Halogen Bonding between Pyridine and Perfluoroalkyl Iodide in Solution Phase Using the Combination of FTIR and¹⁹F NMR

Abstract

Halogen bonding between pyridine and heptafluoro-2-iodopropane (iso-C3F7I)/heptafluoro-1-iodopropane (1-C3F7I) was studied using a combination of FTIR and 19F NMR. The ring breathing vibration of pyridine underwent a blue shift upon the formation of halogen bonds with both iso-C3F7I and 1-C3F7I. The magnitudes of the shifts and the equilibrium constants for the halogen-bonded complex formation were found to depend not only on the structure of the halocarbon, but also on the solvent. The halogen bond also affected the Cα-F (C-F bond on the center carbon) bending and stretching vibrations in iso-C3F7I. These spectroscopic effects show some solvent dependence, but more importantly, they suggest the possibility of intermolecular halogen bonding among iso-C3F7I molecules. The systems were also examined by 19F NMR in various solvents (cyclohexane, hexane, chloroform, acetone, and acetonitrile). NMR dilution experiments support the existence of the intermolecular self-halogen bonding in both iso-C3F7I and 1-C3F7I. The binding constants for the pyridine/perfluoroalkyl iodide halogen bonding complexes formed in various solvents were obtained through NMR titration experiments. Quantum chemical calculations were used to support the FTIR and 19F NMR observations.

Infrared and Raman Measurements of Halogen Bonding in Cryogenic Solutions

“…Typical complexes for which a detailed microwave study is now reported include the complex of ammonia with CF 3 Cl [50] and the 1:1 adducts of CF 3 I with ammonia and trimethylamine [53]. Related complexes recently investigated using IR and NMR spectroscopy [56] are formed between pyridine and the perfluoroalkyl iodides heptafluoro-2-iodopropane (iso-C 3 F 7 I) and heptafluoro-1-iodopropane (1-C 3 F 7 I). …”

“…Before discussing the methodology used and the results obtained during the cryospectroscopic experiments, it is worth noting that, since the first experiments reported in 2009 [48], a variety of complexes strongly related to those studied in the cryosolutions have now also been investigated using traditional and chirped-pulsed microwave studies [49][50][51][52][53][54][55], and that additional information on complexes between more complex perfluoro alkyl iodides and pyridine has also been obtained using low-temperature IR and NMR experiments [56].…”

Halogen-Bond Preferences in Co-crystal Synthesis

“…Twelve co-crystallizations were performed using three acceptor molecules with two different acceptor sites on each of them and four perfluoroiodoalkanes. IR spectroscopy was again found to be a versatile, convenient and accurate screening method for determining if a particular combination of donors and acceptor resulted in the formation of a co-crystal [38][39][40]. With the formation of new intermolecular interactions between donor and acceptor, some of the original stretching bonds are affected although it is sometimes difficult to find obvious patterns to the way in which some of modes are red or blue shifts compared to their original positions.…”

Molecular structures of 3-[(2,2,3,3-tetrafluoropropoxy)methyl]- and 3-[(2,2,3,3,3-pentafluoropropoxy)methyl]pyridinium saccharinates

“…For instance, fluorinated functional groups are incorporated into molecules for novel functions in materials science and in the biomedical field (Kirsch, 2004). A significant number of fluorinated pyridinium salts have been studied with regard to structure and bonding (Hawthorne et al, 2013;Hensen et al, 1988;Mootz & Hocken, 1989), including those with multi-substituted fluorinated side chains (Rocaboy et al, 2002). Pyridine and its derivatives are especially important in modern clinical use, taking advantage of their many biological activities (Altaf et al, 2015).…”