Halogen bonding (XB), an attraction of nucleophiles to electrohilic halogen substituents in various molecules, has emerged in recent years alongside the well-known hydrogen bonding (HB) as driving forces of molecular associations in chemical and biochemical systems. Since many molecules can participate in both XB and HB, accurate interpretations of intermolecular interactions in chemical and biochemical systems require identification and characterization of the co-existing modes of bonding. Such identification relies on the evaluation of similarities and distinctions in these two types of bonding involving the same (XB and HB) donor. Accordingly, the XB and HB complexes between electrophilic halomethanes, R-X (e.g. dihalomethanes or haloforms) and halide anions, X-, co-existing in acetonitrile solutions were identified and characterized via a combination of UV-Vis and NMR spectral measurements with the results of X-ray structural and computational analyses. Halogen-bonded [R-X, X-] complexes displayed strong absorption bands in the UV range and the decreased shift of the NMR signal of R-X protons. Hydrogen bonding led to the opposite (increased) NMR signal shift and the UV-Vis absorption bands of the HB complexes were similar in intensity to that of the separate halosubstituted molecules. The simultaneous multivariable treatment of the results of UV-Vis and NMR titrations afforded formation constants of both XB and HB complexes. DFT computations reproduced well structural, thermodynamic and spectral features of these complexes and demonstrated that variations of the interactions’ strength is directly related to the magnitude of the most positive potentials on the surfaces of the polarized halogen or hydrogen atoms. Non-Covalent Indices (NCI) and Quantum Theory of Atoms in Molecules (QTAIM) analysis of these XB and HB complexes revealed variations of the electron-density topologies in these intermolecular associations and their relationship with the strength of halogen and hydrogen bonding.

Intermolecular interactions of electrophilic halomethanes with halide anions: Halogen vs hydrogen bonding

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.