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1. Trapping of Small Molecules within Single or Double Cyclo[18]carbon Rings

   https://doi.org/10.3390/molecules28052157  

   Trzęsowska, Natasza; Wysokiński, Rafał; Michalczyk, Mariusz; Zierkiewicz, Wiktor; Scheiner, Steve (March 2023, Molecules)

   The encapsulation of a set of small molecules, H2, CO, CO2, SO2, and SO3, by a circular C18 ring is investigated by quantum calculations. These ligands lie near the center of the ring but, with the exception of H2, are disposed roughly perpendicular to the ring plane. Their binding energies with the C18 vary from 1.5 kcal/mol for H2 up to 5.7 kcal/mol for SO2, and the bonding is dominated by dispersive interactions spread over the entire ring. The binding of these ligands on the outside of the ring is weaker but allows the opportunity for each to bond covalently with the ring. A pair of C18 units lie parallel to one another. This pair can bind each of these ligands in the area between them with only small perturbations of the double ring geometry. The binding energies of these ligands to this double ring configuration are amplified by some 50% compared to the single ring systems. The presented data concerning the trapping of small molecules may have larger implications regarding hydrogen storage or air pollution reduction. 

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2. C∙∙∙O and Si∙∙∙O Tetrel Bonds: Substituent Effects and Transfer of the SiF3 Group

   https://doi.org/10.3390/ijms241511884  

   Niu, Zhihao; Wu, Qiaozhuo; Li, Qingzhong; Scheiner, Steve (August 2023, International Journal of Molecular Sciences)

   The tetrel bond (TB) between 1,2-benzisothiazol-3-one-2-TF3-1,1-dioxide (T = C, Si) and the O atom of pyridine-1-oxide (PO) and its derivatives (PO-X, X = H, NO2, CN, F, CH3, OH, OCH3, NH2, and Li) is examined by quantum chemical means. The Si∙∙∙O TB is quite strong, with interaction energies approaching a maximum of nearly 70 kcal/mol, while the C∙∙∙O TB is an order of magnitude weaker, with interaction energies between 2.0 and 2.6 kcal/mol. An electron-withdrawing substituent on the Lewis base weakens this TB, while an electron-donating group has the opposite effect. The SiF3 group transfers roughly halfway between the N of the acid and the O of the base without the aid of cooperative effects from a third entity. 

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3. Methyl‐π Interactions. Nature of Bonding and Limits of Strength

   https://doi.org/10.1002/chem.202404712  

   Scheiner, Steve (February 2025, Chemistry – A European Journal)

   Abstract Both methyl groups and benzene rings are exceedingly common, and they lie near one another in many chemical situations. DFT calculations are used to gauge the strength of the attractive forces between them, and to better understand the phenomena that underlie this attraction. Methane and benzene are taken as the starting point, and substituents of both electron‐withdrawing and donating types are added to each. The interaction energy varies between 1.4 and 5.0 kcal/mol, depending upon the substituents placed on the two groups. The nature of the binding is analyzed via Atoms in Molecules (AIM), Natural Bond Orbital (NBO), Symmetry‐Adapted Perturbation Theory (SAPT), nuclear magnetic resonance (NMR) chemical shifts, and electron density shift diagrams. While there is a sizable electrostatic component, it is dispersion that dominates these interactions, particularly the weaker ones. As such, these interactions cannot be categorized unambiguously as either H‐bonds or tetrel bonds. 

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4. Metal and Ligand Effects on Coordinated Methane pKa: Direct Correlation with the Methane Activation Barrier

   https://doi.org/https://doi.org/10.1021/acs.jpca.0c04756  

   Amy S. Guan, Ivy X. (August 2020, Journal of physical chemistry)

   null (Ed.)

   DFT and coupled cluster methods were used to investigate the impact of 3d metals and ligands upon the acidity and activation of coordinated methane C–H bonds. A strong, direct relationship was established between the pKa of coordinated methane and the free energy barriers (ΔG⧧) to subsequent H3C–H activation. The few outliers to this relationship indicated other salient factors (such as thermodynamic stability of the product and ligand–metal coordination type) that impacted the methane activation barrier. High variations in the activation barriers and pKa values were found with a range of 34.8 kcal/mol for the former and 28.6 pKa units for the latter. Clear trends among specific metals and ligands were also derived; metal ions such as CoI, as well as Lewis acids and π-acids, consistently yielded higher acidity for ligated methane and hence lower ΔG⧧. 

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5. 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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