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1. Computational Study of Ground-State Destabilization Effects and Dipole–Dipole Interaction Energies in Amphidynamic Crystals

   https://doi.org/10.1021/acs.joc.3c00465  

   Liepuoniute, Ieva; Shan, Jing-Ran; Houk, K. N.; Garcia-Garibay, Miguel A. (January 2024, The Journal of Organic Chemistry)

   Scott J. Miller (Ed.)

   Ground state destabilization is a promising strategy to modulate rotational barriers in amphidynamic crystals. DFT studies of polar phenylenes installed as rotators in pillared-paddle wheel metal-organic frameworks were performed to investigate the effects of ground state destabilization on their rotational dynamics. We found that as the steric size of phenylene substituents increases the ground state destabilization effect is also increased. Specifically, a significant destabilization of the ground state energy occurred as the size of the substituents increased, with values ranging from 2 kcal/mol to 11.7 kcal/mol. An evalua-tion of the effects of substituents on dipole-dipole interaction energies and rotational barriers suggest that it should be possi-ble to engineer amphidynamic crystals where the dipole-dipole interaction energy becomes comparable to the rotational barri-ers. Notably, dipole-dipole interaction energies reached values ranging from 0.6 kcal/mol to 2.4 kcal/mol. We propose that careful selection of polar substituents with different size may help create temperature-responsive materials with switchable collective polarization. 

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2. Direct observation of the intermediate in an ultrafast isomerization

   https://doi.org/10.1039/c8sc03258k  

   Porter, Tyler M.; Wang, Jiaxi; Li, Yingmin; Xiang, Bo; Salsman, Catherine; Miller, Joel S.; Xiong, Wei; Kubiak, Clifford P. (January 2019, Chemical Science)

   Using a combination of two-dimensional infrared (2D IR) and variable temperature Fourier transform infrared (FTIR) spectroscopies the rapid structural isomerization of a five-coordinate ruthenium complex is investigated. In methylene chloride, three exchanging isomers were observed: (1) square pyramidal equatorial, ( 1 ); (2) trigonal bipyramidal, ( 0 ); and (3) square pyramidal apical, ( 2 ). Exchange between 1 and 0 was found to be an endergonic process (Δ H = 0.84 (0.08) kcal mol −1 , Δ S = 0.6 (0.4) eu) with an isomerization time constant of 4.3 (1.5) picoseconds (ps, 10 −12 s). Exchange between 0 and 2 however was found to be exergonic (Δ H = −2.18 (0.06) kcal mol −1 , Δ S = −5.3 (0.3) eu) and rate limiting with an isomerization time constant of 6.3 (1.6) ps. The trigonal bipyramidal complex was found to be an intermediate, with an activation barrier of 2.2 (0.2) kcal mol −1 and 2.4 (0.2) kcal mol −1 relative to the equatorial and apical square pyramidal isomers respectively. This study provides direct validation of the mechanism of Berry pseudorotation – the pairwise exchange of ligands in a five-coordinate complex – a process that was first described over fifty years ago. This study also clearly demonstrates that the rate of pseudorotation approaches the frequency of molecular vibrations. 

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3. Deep neural network based quantum simulations and quasichemical theory for accurate modeling of molten salt thermodynamics

   https://doi.org/10.1039/d2sc02227c  

   Shi, Yu; Lam, Stephen T.; Beck, Thomas L. (July 2022, Chemical Science)

   With dual goals of efficient and accurate modeling of solvation thermodynamics in molten salt liquids, we employ ab initio molecular dynamics (AIMD) simulations, deep neural network interatomic potentials (NNIP), and quasichemical theory (QCT) to calculate the excess chemical potentials for the solute ions Na + and Cl − in the molten NaCl liquid. NNIP-based molecular dynamics simulations accelerate the calculations by 3 orders of magnitude and reduce the uncertainty to 1 kcal mol −1 . Using the Density Functional Theory (DFT) level of theory, the predicted excess chemical potential for the solute ion pair is −178.5 ± 1.1 kcal mol −1 . A quantum correction of 13.7 ± 1.9 kcal mol −1 is estimated via higher-level quantum chemistry calculations, leading to a final predicted ion pair excess chemical potential of −164.8 ± 2.2 kcal mol −1 . The result is in good agreement with a value of −163.5 kcal mol −1 obtained from thermo-chemical tables. This study validates the application of QCT and NNIP simulations to the molten salt liquids, allowing for significant insights into the solvation thermodynamics crucial for numerous molten salt applications. 

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4. London Dispersion Effects in a Distannene/Tristannane Equilibrium: Energies of their Interconversion and the Suppression of the Monomeric Stannylene Intermediate

   https://doi.org/10.1002/anie.202301919  

   Zou, Wenxing; Bursch, Markus; Mears, Kristian L.; Stennett, Cary R.; Yu, Ping; Fettinger, James C.; Grimme, Stefan; Power, Philip P. (April 2023, Angewandte Chemie International Edition)

   Abstract Reaction of {LiC₆H₂−2,4,6‐Cyp₃⋅Et₂O}₂(Cyp=cyclopentyl) (1) of the new dispersion energy donor (DED) ligand, 2,4,6‐triscyclopentylphenyl with SnCl₂afforded a mixture of the distannene {Sn(C₆H₂−2,4,6‐Cyp₃)₂}₂(2), and the cyclotristannane {Sn(C₆H₂−2,4,6‐Cyp₃)₂}₃(3).2is favored in solution at higher temperature (345 K or above) whereas3is preferred near 298 K. Van't Hoff analysis revealed the3to2conversion has a ΔH=33.36 kcal mol⁻¹and ΔS=0.102 kcal mol⁻¹ K⁻¹, which gives a ΔG^{300 K}=+2.86 kcal mol⁻¹, showing that the conversion of3to2is an endergonic process. Computational studies show that DED stabilization in3is −28.5 kcal mol⁻¹per {Sn(C₆H₂−2,4,6‐Cyp₃)₂unit, which exceeds the DED energy in2of −16.3 kcal mol⁻¹per unit. The data clearly show that dispersion interactions are the main arbiter of the3to2equilibrium. Both2and3possess large dispersion stabilization energies which suppress monomer dissociation (supported by EDA results). 

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5. Reaction mechanism, energetics, and kinetics of the water-assisted thioformaldehyde + ˙OH reaction and the fate of its product radical under tropospheric conditions

   https://doi.org/10.1039/D0CP00570C  

   Arathala, Parandaman; Katz, Mark; Musah, Rabi A. (May 2020, Physical Chemistry Chemical Physics)

   The reactions of thioformaldehyde (H 2 CS) with OH radicals and assisted by a single water molecule have been investigated using high level ab initio quantum chemistry calculations. The H 2 CS + ˙OH reaction can in principle proceed through: (1) abstraction, and (2) addition pathways. The barrier height for the addition reaction in the absence of a catalyst was found to be −0.8 kcal mol −1 , relative to the separated reactants, which has a ∼1.0 kcal mol −1 lower barrier than the abstraction channel. The H 2 CS + ˙OH reaction assisted by a single water molecule reduces the barrier heights significantly for both the addition and abstraction channels, to −5.5 and −6.7 kcal mol −1 respectively, compared to the un-catalyzed H 2 CS + ˙OH reaction. These values suggest that water lowers the barriers by ∼6.0 kcal mol −1 for both reaction paths. The rate constants for the H 2 CS⋯H 2 O + ˙OH and OH⋯H 2 O + H 2 CS bimolecular reaction channels were calculated using Canonical Variational Transition state theory (CVT) in conjunction with the Small Curvature Tunneling (SCT) method over the atmospherically relevant temperatures between 200 and 400 K. Rate constants for the H 2 CS + ˙OH reaction paths for comparison with the H 2 CS + ˙OH + H 2 O reaction in the same temperature range were also computed. The results suggest that the rate of the H 2 CS + ˙OH + H 2 O reaction is slower than that of the H 2 CS + ˙OH reaction by ∼1–4 orders of magnitude in the temperatures between 200 and 400 K. For example, at 300 K, the rates of the H 2 CS + ˙OH + H 2 O and H 2 CS + ˙OH reactions were found to be 2.2 × 10 −8 s −1 and 6.4 × 10 −6 s −1 , respectively, calculated using [OH] = 1.0 × 10 6 molecules cm −3 , and [H 2 O] = 8.2 × 10 17 molecules cm −3 (300 K, RH 100%) atmospheric conditions. Electronic structure calculations on the H 2 C(OH)S˙ product in the presence of 3 O 2 were also performed. The results show that H 2 CS is removed from the atmosphere primarily by reacting with ˙OH and O 2 to form thioformic acid, HO 2 , formaldehyde, and SO 2 as the main end products. 

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