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1. Triel bonds within anion ··· anion complexes

   https://doi.org/10.1039/D1CP04296C  

   Michalczyk, Mariusz; Zierkiewicz, Wiktor; Wysokiński, Rafał; Scheiner, Steve (November 2021, Physical Chemistry Chemical Physics)

   The ability of two anions to interact with one another is tested in the context of pairs of TrX 4 − homodimers, where Tr represents any of the triel atoms B, Al, Ga, In, or Tl, and X refers to a halogen substituent F, Cl, or Br. None of these pairs engage in a stable complex in the gas phase, but the situation reverses in water where the two monomers are held together by Tr⋯X triel bonds, complemented by stabilizing interactions between X atoms. Some of these bonds are quite strong, notably those involving TrF 4 − , with interaction energies surpassing 30 kcal mol −1 . Others are very much weaker, with scarcely exothermic binding energies. The highly repulsive electrostatic interactions are counteracted by large polarization energies. 

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2. A quantitative assessment of deformation energy in intermolecular interactions: How important is it?

   https://doi.org/10.1063/5.0155895  

   Sargent, Caroline T.; Kasera, Raina; Glick, Zachary L.; Sherrill, C. David; Cheney, Daniel L. (June 2023, The Journal of Chemical Physics)

   Dimer interaction energies have been well studied in computational chemistry, but they can offer an incomplete understanding of molecular binding depending on the system. In the current study, we present a dataset of focal-point coupled-cluster interaction and deformation energies (summing to binding energies, De) of 28 organic molecular dimers. We use these highly accurate energies to evaluate ten density functional approximations for their accuracy. The best performing method (with a double-ζ basis set), B97M-D3BJ, is then used to calculate the binding energies of 104 organic dimers, and we analyze the influence of the nature and strength of interaction on deformation energies. Deformation energies can be as large as 50% of the dimer interaction energy, especially when hydrogen bonding is present. In most cases, two or more hydrogen bonds present in a dimer correspond to an interaction energy of −10 to −25 kcal mol−1, allowing a deformation energy above 1 kcal mol−1 (and up to 9.5 kcal mol−1). A lack of hydrogen bonding usually restricts the deformation energy to below 1 kcal mol−1 due to the weaker interaction energy. 

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3. Systematic characterization of the homogeneous and heterogeneous hydrogen halide dimers

   https://doi.org/10.1063/5.0267887  

   Xue, Yuan; Tschumper, Gregory S (April 2025, The Journal of Chemical Physics)

   This study systematically characterizes the four homogeneous and six heterogeneous hydrogen-bonded dimers formed by hydrogen halide pairs (HX/HY where X, Y = F, Cl, Br, and I). The notation HX⋯HY indicates the direction of the hydrogen bond from the HY donor to the HX acceptor. All stationary points reported for these ten dimer systems are fully optimized utilizing the MP2 and CCSD(T) ab initio methods in conjunction with quadruple-ζ correlation-consistent basis sets augmented with diffuse functions, and their nature is verified by harmonic vibrational frequency computations. The electronic dissociation energies (De) for all ten global minima are evaluated near the CCSD(T) complete basis set (CBS) limit via extrapolation schemes. These values are 19.11, 8.32, 7.38, and 6.22 kJ mol−1 for the homogeneous dimers of HF, HCl, HBr, and HI, respectively. For the heterogeneous pairs, the lighter hydrogen halide is consistently the donor in the global minimum configuration, with De ranging from 12.23 kJ mol−1 for HCl⋯HF to 7.22 kJ mol−1 for HI⋯HBr near the CCSD(T) CBS limit. Interestingly, not all heterodimer donor/acceptor permutations correspond to minima. For example, the HCl⋯HBr configuration is identified as a local minimum at all levels of theory employed in this investigation, whereas the in-plane barrier for donor/acceptor exchange vanishes for HCl⋯HI and HBr⋯HI when larger quadruple-ζ basis sets are utilized. For the seven dimer systems containing Br and/or I, the structures, energetics, and vibrational frequencies computed using conventional valence-only electron correlation procedures are similar to those obtained using an expanded valence treatment that includes the (n − 1)d subvalence electrons associated with Br and I. 

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4. Critical comparison of RX⋯Y and RH⋯Y directionality in halogen and hydrogen bonds using modern computational chemistry methods

   https://doi.org/doi.org/10.1016/j.cplett.2020.137221  

   Riley, Kevin E. (April 2020, Chemical physics letters)

   Symmetry adapted perturbation theory anlysis and intermolecular overlap volume calculations are used to investigate the origins of halogen- and hydrogen bond directionality. The central finding is that exchange-repulsion is primarily responsible for destabilizing both types of interaction as the R-x⋯Y (x = H, Cl, Br) angle deviates from linearity. The particular shape of the electron density envelope on the halogen/hydrogen bond donor plays a large role in dictating the degree to which a complex is destabilized upon R-x⋯Y rotation, with halogen bonds exhibiting a roughly linear destabilization and hydrogen bonds exhibiting destabilization that is approximately quadratic. 

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5. The non-covalently bound SO⋯H ₂ O system, including an interpretation of the differences between SO⋯H ₂ O and O ₂ ⋯H ₂ O

   https://doi.org/10.1039/C8CP05749D  

   Misiewicz, Jonathon P.; Noonan, Julia A.; Turney, Justin M.; Schaefer, Henry F. (November 2018, Physical Chemistry Chemical Physics)

   Despite the interest in sulfur monoxide (SO) among astrochemists, spectroscopists, inorganic chemists, and organic chemists, its interaction with water remains largely unexplored. We report the first high level theoretical geometries for the two minimum energy complexes formed by sulfur monoxide and water, and we report energies using basis sets as large as aug-cc-pV(Q+d)Z and correlation effects through perturbative quadruple excitations. One structure of SO⋯H 2 O is hydrogen bonded and the other chalcogen bonded. The hydrogen bonded complex has an electronic energy of −2.71 kcal mol −1 and a zero kelvin enthalpy of −1.67 kcal mol −1 , while the chalcogen bonded complex has an electronic energy of −2.64 kcal mol −1 and a zero kelvin enthalpy of −2.00 kcal mol −1 . We also report the transition state between the two structures, which lies below the SO⋯H 2 O dissociation limit, with an electronic energy of −1.26 kcal mol −1 and an enthalpy of −0.81 kcal mol −1 . These features are much sharper than for the isovalent complex of O 2 and H 2 O, which only possesses one weakly bound minimum, so we further analyze the structures with open-shell SAPT0. We find that the interactions between O 2 and H 2 O are uniformly weak, but the SO⋯H 2 O complex surface is governed by the superior polarity and polarizability of SO, as well as the diffuse electron density provided by sulfur's extra valence shell. 

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