Resolving the halogen vs. hydrogen bonding dichotomy in solutions: intermolecular complexes of trihalomethanes with halide and pseudohalide anions

Abstract

Halogen- and hydrogen-bonded complexes between trihalomethanes, CHX3, and (pseudo-)halide anions, A-, 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 [CHX3, A-] complexes displayed strong absorption bands in the UV range (showing Mulliken correlations with the frontier orbital energies of the interacting species) and a decreased shift of the NMR signal of trihalomethanes' protons. Hydrogen bonding led to the opposite (increased) NMR signal shift and the UV-vis absorption bands of the hydrogen-bonded [CHX3, A-] complexes were similar in intensity to those of the separate CHX3 molecules. The simultaneous multivariable treatment of the results of UV-vis and NMR titrations of CHX3 with A- anions afforded formation constants of both halogen- and hydrogen-bonded complexes between these species, which existed side-by-side in the acetonitrile solutions. The relative values of the formation constants were consistent with the magnitudes of the positive potentials on the surfaces of the halogen or hydrogen atoms if the effects of the polarization of the trihalomethanes due to the presence of the anions were taken into account.

Molecular Bases for Anesthetic Agents: Halothane as a Halogen‐ and Hydrogen‐Bond Donor

“…Thus, while the NMR measurements indicated the presence of HB complexes in the acetonitrile solutions of halothane and DABCO or iodide, the UV/Vis measurements pointed out HaB formation in the same systems. Simultaneous fitting of the NMR and UV/Vis spectral data measured in the solutions with constant concentration of halothane and variable concentrations of iodide yielded formation constants of HaB and HB complexes of about 0.2 m −1 and 0.5 m −1 , respectively (Figure S13) . A similar treatment of the data obtained in solutions of halothane with DABCO yielded formation constants of about 0.2 and 0.4 m −1 for HaB and HB complexes, respectively.…”

“…In general, the formation of HB and HaB complexes results in distinct NMR‐ and UV/Vis‐spectral changes . For example, the formation of HaBs or HBs between trihalomethanes and anions leads, in NMR spectra, to the opposite shift of proton signals and, in UV/Vis spectra, to the appearance of new absorption bands (HaBs) or a shift of the absorption bands of the reactants (HBs) …”

Effects of Halogen, Chalcogen, Pnicogen, and Tetrel Bonds on IR and NMR Spectra

“…However, while a good deal of information has accumulated in recent years concerning certain aspects of the halogen and related bonds, there is less information available concerning their spectra. The data that has appeared [36,53,54,55,56,57,58,59,60,61,62] has been informative, but does not consider these systems in a systematic manner. As such, currently, there is no thorough account of the manner in which each sort of interaction modulates the spectra, nor a solid understanding of the contributing factors.…”

Intermolecular Interactions between Halogen‐Substituted p‐Benzoquinones and Halide Anions: Anion‐π Complexes versus Halogen Bonding

“…The effect of polarization is especially pronounced in the complexes involving charged species. For example, we have shown earlier that the formation constants of XB and HB complexes of trihalomethanes (CHX 3 ) with halide anions are highly correlated with the values of maximum potentials on the surfaces of halogen and hydrogen atoms of CHX 3 only if polarizations of these molecules in XB and HB complexes were taken into account . In a similar way, the ESPs of BQ molecules are substantially altered in the presence of neighboring anions and the magnitudes of changes are determined by the position of the latter.…”

“…For example, we have shown earlier that the formation constants of XB and HB complexes of trihalomethanes (CHX 3 ) with halide anions are highly correlated with the values of maximum potentials on the surfaces of halogen and hydrogen atoms of CHX 3 only if polarizations of these molecules in XB and HB complexes were taken into account. [28] In a similar way, the ESPs of BQ molecules are substantially altered in the presence of neighboring anions and the magnitudes of changes are determined by the position of the latter. Specifically, the XB anions increase the potential on the surfaces of the bonded halogen substituents, while the πbonded halides increase V max π on the surfaces of the BQ rings facing this anion.…”