Enhanced Aerogen-π Interaction by a Cation-π Force

Exploring Unconventional σ-Hole Interactions: Computational Insights into the Interaction of XeO3 with Non-Aromatic Coordinating Solvents

In order to control the explosiveness and shock sensitivity of XeO3 , we have investigated its plausible interaction with various non-aromatic coordinating solvents, serving as potential Lewis base donors, through density functional theory (DFT) calculations. Out of twenty six such solvents, the top ten were thus identified and then thoroughly examined by employing various computational tools such as the mapping of the electrostatic potential surface (MESP), Wiberg bond indices (WBIs), non-covalent interaction (NCI) plots, Bader's theory of atoms-in-molecules (AIM), natural bond orbital (NBO) analysis, and the energy decomposition analysis (EDA). The amphoteric nature of XeO3 was also explored by investigating the extent of back donation from the lone pair of Xe to the antibonding orbital of the donating atom/group of the solvent molecules. The C-H…O interactions were also found to be a contributing factor in the stabilization of these adducts. Although these aerogen-bonding interactions were found to be predominantly electrostatic, significant contributions from the orbital contributions, as well as dispersion interactions, were observed. The top three non-aromatic solvents (among the twenty six studied) which form the strongest adducts with XeO3 are proposed to be hexamethylphosphoramide (HMPA), N,N'-dimethylpropyleneurea (DMPU) and tetramethylethylenediamine (TMEDA).

Size Matters: Computational Insights into the Crowning of Noble Gas Trioxides

In pursuit of enhancing the stability of the highly explosive and shock-sensitive compound XeO3, we performed quantum chemical calculations to investigate its possible complexation with electron-rich crown ethers, including 9-crown-3, 12-crown-4, 15-crown-5, 18-crown-6, and 21-crown-7, as well as their thio analogues. Furthermore, we expanded our study to other noble gas trioxides (NgO3), namely, KrO3 and ArO3. The basis set superposition error (BSSE) corrected interaction energies for these adducts range from -13.0 kcal/mol to -48.2 kcal/mol, which is notably high for σ-hole-mediated noncovalent interactions. The formation of these adducts was observed to be more favorable with the increase in the ring size of the crowns and less favorable while going from XeO3 to ArO3. A comprehensive analysis by various computational tools such as the mapping of the electrostatic potential (ESP), Wiberg bond indices (WBIs), Bader's theory of atoms-in-molecules (AIM), natural bond orbital (NBO) analysis, noncovalent interaction (NCI) plots, and energy decomposition analysis (EDA) revealed that the C-H···O interactions, as well as dispersion interactions, play a pivotal role in stabilizing adducts involving larger crowns. A noteworthy outcome of our study is the revelation of a coordination number of 9 for xenon in the complex formed between XeO3 and the thio analogue of 18-crown-6, which is higher than the largest number reported to date.

Hole interactions of aerogen oxides with Lewis bases: an insight into σ-hole and lone-pair-hole interactions

σ-Hole and lone-pair (lp)-hole interactions of aerogen oxides with Lewis bases (LB) were comparatively inspected in terms of quantum mechanics calculations. The ZOn ⋯ LB complexes (where Z = Kr and Xe, n = 1, 2, 3 and 4, and LB = NH3 and NCH) showed favourable negative interaction energies. The complexation features were explained in light of σ-hole and lp-hole interactions within optimum distances lower than the sum of the respective van der Waals radii. The emerging findings outlined that σ-hole interaction energies generally enhanced according to the following order: KrO4 ⋯ < KrO⋯ < KrO3⋯ < KrO2⋯LB and XeO4⋯ < XeO⋯ < XeO2⋯ < XeO3⋯LB complexes with values ranging from -2.23 to -12.84 kcal mol-1. Lp-hole interactions with values up to -5.91 kcal mol-1 were shown. Symmetry-adapted perturbation theory findings revealed the significant contributions of electrostatic forces accounting for 50-65% of the total attractive forces within most of the ZOn⋯LB complexes. The obtained observations would be useful for the understanding of hole interactions, particularly for the aerogen oxides, with application in supramolecular chemistry and crystal engineering.

Noncovalent chemistry of xenon opens the door for anesthetic xenon recovery using Bio-MOFs

Designing an inexpensive and highly efficient recovery process for xenon (Xe) is gaining importance in the development of sustainable applications. Using metal organic frameworks (MOFs) for separating Xe from anesthetic gas mixtures has been a recent topic studied rarely and superficially in the literature. We theoretically investigated Xe recovery performances of 43 biological MOFs (Bio-MOFs) formed by biocompatible metal cations and biological endogenous linkers. Xe uptakes and Xe permeabilities in its binary mixtures with CO2, O2, and N2 were investigated by applying Grand Canonical Monte Carlo and Molecular Dynamics simulations. Materials with metalloporphyrin, hexacarboxylate, triazine, or pyrazole ligands, dimetallic paddlewheel units, relatively large pore sizes (PLD > 5 Å and LCD > 10 Å), large void fractions (≈0.8), and large surface areas (>2900 m2 g-1) have been determined as top performing Bio-MOFs for Xe recovery. By applying Density Functional Theory simulations and generating electron density difference maps, we determined that Xe-host interactions in the top performing Bio-MOFs are maximized mainly due to noncovalent interactions of Xe, such as charge-induced dipole and aerogen-π interactions. Polarized Xe atoms in the vicinity of cations/anions as well as π systems are fingerprints of enhanced guest-host interactions. Our results show examples of rarely studied aerogen interactions that play a critical role in selective adsorption of Xe in nanoporous materials.

Synergistic and Diminutive Effects between Regium and Aerogen Bonds

The aerogen bond is formed in complexes of HCN-XeF₂ O and C₂ H₄ -XeF₂ O. The lone pair on the N atom of HCN is a better electron donor in the aerogen bond than the π electron on the C=C bond of C₂ H₄ . The coinage substitution strengthens the aerogen bond in MCN-XeF₂ O (M=Cu, Ag, and Au) and its enhancing effect becomes larger in the Au<Cu<Ag pattern. The aerogen bond is further enhanced by the regium bond in C₂ H₂ -MCN-XeF₂ O and C₂ H₄ -MCN-XeF₂ O, but is weakened by the regium bond in MCN-C₂ H₄ -XeF₂ O and C₂ (CN)₄ -MCN-XeF₂ O. Simultaneously, the regium bond is also strengthened or weakened in these triads. The synergistic and diminutive effects between regium and aerogen bonds have been explained by means of charge transfer and electrostatic potentials.

Xe⋯chalcogen aerogen bond. Effect of substituents and size of chalcogen atom

We have studied the effect of substituent and size of chalcogen atom on the aerogen bond between F₂XeO and R₁YR₂.

Unexpectedly strong Xe binding by host-guest interaction

A unique noncovalent interaction between XeO₃ and 18-crown-6 has been studied by density functional theory. The calculated results show that there exists an extremely strong binding force between both species, reaching 36.44 kcal mol^-1, which is comparable to the strong cation-π interaction. Detailed analyses on relaxed force constants, electrostatic potentials and the independent gradient model, etc. suggest that both quite strong aerogen bondings (XeO) and relatively weak unconventional H-bondings (C-HO) coexist, and the complex is a typical heterodimer with multiple binding sites. Further studies found that XeO₃ takes a quick rotary motion relative to 18-crown-6 in the complex due to low rotary barrier. Another two guest molecules, KrO₃ and ArO₃, are also discussed.

The effects of aerogen-bonding on the geometries and spectral properties of several small molecular clusters containing XeO3

Aerogen bonding, as a specific noncovalent interaction, has attracted wide attention recently. A number of theoretical studies have proposed this effect based on the analysis of electronic structures of aerogen-containing systems though, the spectral characteristics have not been identified, which becomes the obstacle for the experimental confirmation of this interaction. In this paper, we employed the density functional theory to explore the energetic and geometric properties, infrared, Raman spectra of five small molecular clusters XeO₃·H₂O, XeO₃·NH₃, XeO₃ dimer, XeO₃ trimer, and XeO₃·2H₂O. Our results show the binding energies of the most favorable conformations for the dimers are larger than  -10.00 kcal mol^-1 and those for trimers are larger than  -20.00 kcal mol^-1, which indicates the strong aerogen bonding is favorable for the stabilities of these clusters. More importantly, some new IR and Raman vibrations at fingerprint region (<1000 cm^-1) are identified, which corresponds to the formation of aerogen bonds. This study provides a viable way for the experimentalists to characterize the aerogen bonding in future.

Cooperativity between the hydrogen bonding and σ-hole interaction in linear NCX···(NCH)n=2–5 and O3Z···(NCH)n=2–5 complexes (X = Cl, Br; Z = Ar, Kr): a comparative study

Quantum chemical calculations are performed to investigate the cooperativity of hydrogen bonding with halogen or aerogen bonding interactions in linear NCX···(NCH)n=2–5 and O3Z···(NCH)n=2–5 clusters, where X = Cl, Br and Z = Ar, Kr. To understand the cooperativity mechanism in these systems, the corresponding binary NCX···NCH and O3Z···NCH complexes are also considered. The binding distances, interaction energies, and bonding properties of the NCX···(NCH)n=2–5 and O3Z···(NCH)n=2–5 clusters are analyzed in detail. It is found that the cooperative effects in the hydrogen bonding tend to strengthen X···N and Z···N interactions. For both NCX···(NCH)n and O3Z···(NCH)n clusters, a small bond shrinkage is observed from n = 4 to n = 5, which suggests that the cooperativity effects are almost saturated in the larger clusters (n > 5). As the size of the X or Z atom is increased, the magnitude of the cooperative energy in these systems is also increased, which is mainly ascribed to changes in electrostatic potentials and orbital interactions. Our results indicate that the cooperative effects lead to a substantial change in the 14N nuclear quadrupole coupling constants of the NCH molecule.

DFT studies on the heterogeneous oxidation of SO2 by oxygen functional groups on graphene

Conversion of SO₂ to SO₃ on oxygen-functionalized graphene under ambient conditions.