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1. DFT study on binding of single and double methane with aromatic hydrocarbons and graphene: stabilizing CH…HC interactions between two methane molecules

   Jovian Lazare, Dalia Daggag ( October 2020 , Structural chemistry)

   Density functional theory (DFT) calculations were used to examine the binding strength of one and two methane molecule(s) with graphene (62 and 186 carbon atoms) and model systems of aromatic hydrocarbons (benzene, pyrene, and coronene). We explored different possibilities of binding modes of methane such as one, two, and three C-H interacting with small π-systems. Two methane molecules were considered to bind from the same as well as opposite sides of the plane of benzene and other πsystems including graphene models. Our results show that methane molecule prefers to bind with three C-H…π interactions with all the π-systems except benzene. The preference of tripod configuration of methane on the surface of graphene systems strongly agrees with the neutron diffraction experiment of methane on graphitized carbon black. The binding strength is almost doubled by increasing the number of methane molecules from one to two. Importantly, two methane molecules prefer to bind on the same side rather than opposite sides of the plane of graphene due to stabilizing CH…HC interactions between them in addition to six CH…π interactions. Interestingly, binding strength contributions from CH…HC interactions (approx. 0.4–0.5 kcal/mol) of two methane molecules on the surface are analogous to methane dimer complex freemore »from the surface of graphene. C-H stretching frequency shifts, bond lengths, and binding distances support the presence of CH…HC interactions between two methane molecules. Structures of complexes, binding energies, and C-H stretching frequency shifts agree with available experimental data« less
2. Towards and understanding of CO2 microsolvation: Microwave spectroscopy of CO2 complexes with fluoroethylenes

   Peebles, Rebecca A. ; Peebles, Sean A. ; Anderton, Ashley M. ; Christenholz, Cori L. ; Dorris, Rachel E. ; Trendell, William C. ( August 2017 , 254th American Chemical Society National Meeting)

   The need for a deep understanding of CO2 interactions with other mols. is significant given the importance of supercrit. CO2 (s.c.-CO2) as a green solvent, and interest in design of novel materials for CO2 capture and storage. Soly. of fluorinated compds. in s.c.-CO2 is generally higher than their hydrocarbon analogs and fluorination of hydrocarbon compds. improves "CO2-philicity". Although dissoln. of a compd. in s.c.-CO2 (or any solvent) is a complex process, much can be learned by systematic examn. of solute-solvent interactions as a function of solute mol. properties in dimers and other small clusters. In the present study, Fourier-transform microwave spectroscopy and Symmetry Adapted Perturbation Theory (SAPT) calcns. have been used to examine intermol. interactions between CO2 and a series of fluorinated ethylene mols. with varying degree and position of fluorination (1-3 F atoms). While 1-fluoro-, 1,1-difluoro- and 1,1,2-trifluoroethylene...CO2 complexes are planar (with two isomers obsd. for 1-fluoroethylene), cis-1,2-difluoroethylene...CO2 is nonplanar. Although lowest energy structures predicted by MP2/6-311++G(2d,2p) calcns. are not always in agreement with obsd. configurations, SAPT calcns. provide binding energies consistent with the obsd. structures. We are now extending these studies to trimers contg. one fluorinated ethylene with two CO2 "solvent" mols. in order to gain further insightmore »into structural and energetic changes as a solvation shell is formed.« less
3. A generalized Rayleigh-Plesset equation for ions with solvent fluctuations

   Fan, C. ; Li, B. ; White, M. ( June 2021 , SIAM journal on applied mathematics)

   We introduce a mathematical modeling framework for the conformational dynamics of charged molecules (i.e., solutes) in an aqueous solvent (i.e., water or salted water). The solvent is treated as an incompressible fluid, and its fluctuating motion is described by the Stokes equation with the Landau–Lifschitz stochastic stress. The motion of the solute-solvent interface (i.e., the dielectric boundary) is determined by the fluid velocity together with the balance of the viscous force,hydrostatic pressure, surface tension, solute-solvent van der Waals interaction force, and electrostatic force. The electrostatic interactions are described by the dielectric Poisson–Boltzmann theory.Within such a framework, we derive a generalized Rayleigh–Plesset equation, a nonlinear stochastic ordinary differential equation (SODE), for the radius of a spherical charged molecule, such as anion. The spherical average of the stochastic stress leads to a multiplicative noise. We design and test numerical methods for solving the SODE and use the equation, together with explicit solvent molecular dynamics simulations, to study the effective radius of a single ion. Potentially, our general modeling framework can be used to efficiently determine the solute-solvent interfacial structures and predict the free energies of more complex molecular systems.
4. A comparison between hydrogen and halogen bonding: the hypohalous acid–water dimers, HOX⋯H ₂ O (X = F, Cl, Br)

   https://doi.org/10.1039/C9CP00422J  

   Wolf, Mark E. ; Zhang, Boyi ; Turney, Justin M. ; Schaefer, Henry F. ( March 2019 , Physical Chemistry Chemical Physics)

   Hypohalous acids (HOX) are a class of molecules that play a key role in the atmospheric seasonal depletion of ozone and have the ability to form both hydrogen and halogen bonds. The interactions between the HOX monomers (X = F, Cl, Br) and water have been studied at the CCSD(T)/aug-cc-pVTZ level of theory with the spin free X2C-1e method to account for scalar relativistic effects. Focal point analysis was used to determine CCSDT(Q)/CBS dissociation energies. The anti hydrogen bonded dimers were found with interaction energies of −5.62 kcal mol −1 , −5.56 kcal mol −1 , and −4.97 kcal mol −1 for X = F, Cl, and Br, respectively. The weaker halogen bonded dimers were found to have interaction energies of −1.71 kcal mol −1 and −3.03 kcal mol −1 for X = Cl and Br, respectively. Natural bond orbital analysis and symmetry adapted perturbation theory were used to discern the nature of the halogen and hydrogen bonds and trends due to halogen substitution. The halogen bonds were determined to be weaker than the analogous hydrogen bonds in all cases but close enough in energy to be relevant, significantly more so with increasing halogen size.
5. Anion–anion and anion–neutral triel bonds

   https://doi.org/10.1039/D0CP06547A  

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

   The ability of a TrCl 4 − anion (Tr = Al, Ga, In, Tl) to engage in a triel bond with both a neutral NH 3 and CN − anion is assessed by ab initio quantum calculations in both the gas phase and in aqueous medium. Despite the absence of a positive σ or π-hole on the Lewis acid, strong triel bonds can be formed with either base. The complexation involves an internal restructuring of the tetrahedral TrCl 4 − monomer into a trigonal bipyramid shape, where the base can occupy either an axial or equatorial position. Although this rearrangement requires a substantial investment of energy, it aids the complexation by imparting a much more positive MEP to the site that is to be occupied by the base. Complexation with the neutral base is exothermic in the gas phase and even more so in water where interaction energies can exceed 30 kcal mol −1 . Despite the long-range coulombic repulsion between any pair of anions, CN − can also engage in a strong triel bond with TrCl 4 − . In the gas phase, complexation is endothermic, but dissociation of the metastable dimer is obstructed by an energy barrier. Themore »situation is entirely different in solution, with large negative interaction energies of as much as −50 kcal mol −1 . The complexation remains an exothermic process even after the large monomer deformation energy is factored in.« less