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1. Characterization of competing halogen-bonding and hydrogen-bonding motifs in the acetonitrile/hydrogen iodide dimer

   https://doi.org/10.1016/j.chemphys.2023.111843  

   Perkins, Morgan A.; Tschumper, Gregory S. (April 2023, Chemical Physics)
2. On the nature of hydrogen bonding in the H2S dimer

   https://doi.org/10.1038/s41467-024-53444-6  

   Jäger, Svenja; Khatri, Jai; Meyer, Philipp; Henkel, Stefan; Schwaab, Gerhard; Nandi, Apurba; Pandey, Priyanka; Barlow, Kayleigh R; Perkins, Morgan A; Tschumper, Gregory S; et al (December 2024, Nature Communications)

   Abstract Hydrogen bonding is a central concept in chemistry and biochemistry, and so it continues to attract intense study. Here, we examine hydrogen bonding in the H₂S dimer, in comparison with the well-studied water dimer, in unprecedented detail. We record a mass-selected IR spectrum of the H₂S dimer in superfluid helium nanodroplets. We are able to resolve a rotational substructure in each of the three distinct bands and, based on it, assign these to vibration-rotation-tunneling transitions of a single intramolecular vibration. With the use of high-level potential and dipole-moment surfaces we compute the vibration-rotation-tunneling dynamics and far-infrared spectrum with rigorous quantum methods. Intramolecular mode Vibrational Self-Consistent-Field and Configuration-Interaction calculations provide the frequencies and intensities of the four SH-stretch modes, with a focus on the most intense, the donor bound SH mode which yields the experimentally observed bands. We show that the intermolecular modes in the H₂S dimer are substantially more delocalized and more strongly mixed than in the water dimer. The less directional nature of the hydrogen bonding can be quantified in terms of weaker electrostatic and more important dispersion interactions. The present study reconciles all previous spectroscopic data, and serves as a sensitive test for the potential and dipole-moment surfaces. 

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3. Matrix effects on hydrogen bonding and proton transfer in fluoropyridine – HCl complexes

   https://doi.org/10.1039/d1cp04110j  

   Soares, Camilla; Ley, Anna R.; Zehner, Brittany C.; Treacy, Patrick W.; Phillips, James A. (January 2022, Physical Chemistry Chemical Physics)

   We report an extensive computational and spectroscopic study of several fluoropyridine–HCl complexes, and the parent, pyridine–HCl system. Matrix-IR spectra for pentafluoropyridine–HCl, 2,6-difluororpyridine–HCl, and 3,5-difluororpyridine–HCl in solid neon exhibit shifts for the H–Cl stretching band that parallel the effects of fluorination on hydrogen-bond strength. Analogous spectral shifts observed across various host environments (solid neon, argon, and nitrogen) for pentafluoropyridine–HCl and 2,6-difluororpyridine–HCl convey a systematically varying degree of matrix stabilization on the hydrogen bonds in these complexes. An extended quantum-chemical study of pyridine–HCl and eight fluorinated analogs, including 2-, 3-, and 4-fluoropyridine–HCl, 2,6- and 3,5-difluororpyridine–HCl, 2,4,6- and 3,4,5-trifluropyridine–HCl, as well as pentafluoropyridine–HCl, was also performed. Equilibrium structures and binding energies for the gas-phase complexes illustrate two clear trends in how fluorine substitution affects hydrogen bond strength; increasing fluorination weakens these interactions, yet substitution at the 2- and 6-positions has the most pronounced effect. Bonding analyses for a select subset of these systems reveal shifts in electron density that accompany hydrogen bonding, and most notably, the values of the electron density at the N–H bond critical points among the stronger systems in this subset significantly exceed those typical for moderately strong hydrogen-bonds. We also explored the effects of dielectric media on the structural and bonding properties of these systems. For pyridine–HCl, 3-fluoropyridine–HCl, and 3,5-difluororpyridine–HCl, a transition to proton transfer-type structures is observed at ε -values of 1.2, 1.5, and 2.0, respectively. This is signaled by key structural changes, as well as an increase in the negative charge on the chorine, and dramatic shifts in topological properties of the H–Cl and N–H bonds. In the case of pentafluoropyridine–HCl, and 2,6-difluororpyridine–HCl, we do not predict proton transfer in dielectric media up to ε = 20.0. However, there are clear indications that the media enhance hydrogen-bond strength, and moreover, these observations are completely consistent with the experimental IR spectra. 

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4. Infrared spectroscopy of the protonated HCl dimer and trimer

   https://doi.org/10.1063/5.0065477  

   Wagner, J. Philipp; McDonald, David C.; Colley, Jason E.; Franke, Peter R.; Duncan, Michael A. (October 2021, The Journal of Chemical Physics)
5. Dissociation energy of the HCN⋯HF dimer

   https://doi.org/10.1016/j.cplett.2020.137382  

   Sexton, Thomas More; Van Benschoten, William Zeller; Tschumper, Gregory S. (June 2020, Chemical Physics Letters)