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

Briauna Hawthorne,Jessica Smith,Elizabeth Wood,Timothy Hanks,Haiyan Fan-Hagenstein

doi:10.1155/2013/216518

Briauna Hawthorne, Jessica Smith + Show 3 more

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https://doi.org/10.1155/2013/216518

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Abstract

Halogen bonding between pyridine and heptafluoro-2-iodopropane (iso-C3F7I)/heptafluoro-1-iodopropane (1-C3F7I) was studied using a combination of FTIR and19F 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 by19F 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 and19F NMR observations.

Highlights

Halogen bonding, a noncovalent interaction between a halogen atom acting as an electron acceptor and an electronrich Lewis base, has been known for nearly 150 years [1,2,3,4,5,6]
Of particular importance are their presentations of detailed thermodynamic parameters measured for the halogen bonding systems made of organic donors and halogen anions in the solution phase and which emphasized their importance in the anion recognition
The ring breathing vibration of pyridine was found to be blue shifted on the formation of halogen bonding complex with iso-C3F7I and 1-C3F7I

Summary

Introduction

A noncovalent interaction between a halogen atom acting as an electron acceptor and an electronrich Lewis base, has been known for nearly 150 years [1,2,3,4,5,6]. Focusing on the halogen bond impact on the perfluoroalkyl iodide, Messina et al [43] led the study of the systems between α, ω-diiodoperfluoroalkanes, and other electron donors using FTIR and Raman spectroscopy. Fan and coworkers [44] studied the pyridine and perfluoroalkyl iodides Their observations led to a hypothesis that there existed some self-intermolecular halogen bond among iso-C3F7I molecules in the liquid phase, while this self-intermolecular halogen bond did not exist or at least was very weak for 1-C4F9I and 1-C6F13I. The thermodynamics of the halogen bond for the system between pyridine and perfluoroalkyl iodides in solution phase was studied using the combination of the results from FTIR and 19F NMR measurements

Experimental Section

Result and Discussion

Conclusion