Quantum Chemical Investigation of Attractive Non-Covalent Interactions between Halomethanes and Rare Gases

The Origin of the σ-Hole in Halogen Atoms: a Valence Bond Perspective

A detailed Valence Bond-Spin Coupled analysis of a series of halogenated molecules is here reported, allowing to get a rigorous ab initio demonstration of the qualitative models previously proposed to explain the origin of halogen bonding. The concepts of σ-hole and negative belt observed around the halogen atoms in the electrostatic potential maps are here interpreted by analysis of the relevant Spin Coupled orbitals.

Halogen Bonding from the Bonding Perspective with Considerations for Mechanisms of Thyroid Hormone Activation and Inhibition

Halogen bonding interactions are often discussed in terms of an area of positive electrostatic potential on the halogen center along the bond axis called the σ-hole, yet various authors have noted a lack of completeness in this model. The nature of the XB interaction is explored from the perspective of bonding theories beginning from models that explain the electrostatic σ-hole and continuing to orbital-based donor-acceptor descriptions in which the donor lone pair MO mixes with the acceptor R-X and R-X* MOs to form a set of XB MOs related to three-center-four-electron bonding in hypervalent molecules. The strength of the XB interaction for a large series of RX···Cl- and RX···SeMe2 complexes correlate well with the energy of the acceptor R-X* MO and the contribution of the halide to the R-X and R-X* MOs, factors relevant to favourable overlap with the donor lone pair. An orbital-based focus accounts for the partial covalency of the XB interaction and can be extended to descriptions of enzymatic dehalogenation mechanisms. Applications of this MO perspective to the deiodination of thyroid hormones by the iodothyronine deiodinases and a possibly related mechanism of inhibition are discussed.

Carbon flakes based metal organic frameworks for H2, CH4 and CO2 gas storage: a GCMC simulation study

In this study, new metal organic frameworks have been designed by modifying the linker of IRMOF-1 with different carbon flakes (circular, rectangular and rhombus).

Computational and Experimental Investigation of the Detection of HO2 Radical and the Products of Its Reaction with Cyclohexene Ozonolysis Derived RO2 Radicals by an Iodide-Based Chemical Ionization Mass Spectrometer

The HO₂ radical is an important atmospheric molecule that can potentially influence the termination of autoxidation processes of volatile organic compounds (VOCs) that lead to the formation of highly oxygenated multifunctional compounds (HOMs). In this work, we demonstrate the direct detection of the HO₂ radical using an iodide-based chemical ionization mass spectrometer (iodide-CIMS). Expanding on the previously established correlation between molecule-iodide binding enthalpy and iodide-CIMS instrument sensitivity, the experimental detection of the HO₂ radical was preceded by the quantum chemical calculation of the HO₂*I^- cluster (PBE/aug-cc-pVTZ-PP level), which showed a reasonably strong binding enthalpy of 21.60 kcal/mol. Cyclohexene ozonolysis intermediates and closed-shell products were next detected by the iodide-CIMS. The ozone-initiated cyclohexene oxidation mechanism was perturbed by the introduction of the HO₂ radical, leading to the formation of closed-shell hydroperoxides. The experimental investigation once again followed the initial computational molecule-iodide binding enthalpy calculations. The quantum chemical calculations were performed at the PBE/aug-cc-pVTZ-PP level for radicals and DLPNO-CCSD(T)/def2-QZVPP//PBE/aug-cc-pVTZ-PP level for the closed-shell products. A comparison between the iodide-CIMS and nitrate-CIMS spectra with identical measurement steps revealed that the iodide-CIMS was able to detect the low-oxidized (O/C ratio 0.5 and 0.66) cyclohexene ozonolysis monomer products more efficiently than nitrate-CIMS. Higher-oxidized monomers (O/C ratio 1 to 1.5) were detected equally well by both methods. An investigation of dimers showed that both iodide- and nitrate-CIMS were able to detect the dimer compositions possibly formed from reactions between the peroxy radical monomers considered in this study. Additionally, iodide-CIMS detected organic ions that were formed by a previously suggested mechanism of dehydroxylation of peroxy acids (and deoxygenation of acyl peroxy radicals) by H₂O*I^- clusters. These mechanisms were computationally verified.

Investigations of the Rg-BrCl (Rg=He, Ne, Ar, Kr, Xe) binary van der Waals complexes: ab initio intermolecular potential energy surfaces, vibrational states and predicted pure rotational transition frequencies

The intermolecular potential energy surfaces (PESs) of the ground electronic state for the Rg-BrCl (Rg=He, Ne, Ar, Kr, Xe) van der Waals complexes have been constructed by using the coupled-cluster method in combination with the augmented quadruple-zeta correlation-consistent basis sets supplemented with an additional set of bond functions. The features of the anisotropic PESs for these complexes are remarkably similar, which are characterized by three minima and two saddle points between them. The global minimum corresponds to a collinear Rg-Br-Cl configuration. Two local minima, correlate with an anti-linear Rg-Cl-Br geometry and a nearly T-shaped structure, can also be located on each PES. The quantum bound state calculations enable us to investigate intermolecular vibrational states and rotational energy levels of the complexes. The transition frequencies are predicted and are fitted to obtain their corresponding spectroscopic constants. In general, the periodic trends are observed for this complex family. Comparisons with available experimental data for the collinear isomer of Ar-BrCl demonstrate reliability of our theoretical predictions, and our results for the other two isomers of Ar-BrCl as well as for other members of the complex family are also anticipated to be trustable. Except for the collinear isomer of Ar-BrCl, the data presented in this paper would be beneficial to improve our knowledge for these experimentally unknown species.

A solvent-resistant halogen bond

In contrast to strong hydrogen bonds, strong halogen bonds are not disrupted by polar solvents.

Theoretical insights into the nature of halogen bonding in prereactive complexes

Benchmark quality geometries and interaction energies for the prereactive halogen-bonded complexes of dihalogens and ammonia, including hypothetical astatine containing dihalogens, have been produced via explicitly correlated coupled cluster methods. The application of local electron correlation partitioning reveals dispersion, electrostatics and ionic substitutions all contribute significantly to the interaction energy, with a linear relationship between the ionic substitutions and the degree of charge transfer. Potential energy curves for H3 N⋅⋅⋅ClF show that as the relative orientations of the two subunits are manipulated appreciable interactions can be found at considerably angular displaced geometries, signifying lower directionality in halogen bonding than previously supposed.