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.

Reactivity of pyrazole derivatives with halomethanes: A DFT theoretical study

The N-alkylation reaction of pyrazole derivatives with halomethanes was studied using density functional theory (DFT). The hybrid method B3LYP was employed, along with an ECP basis set such as LANL2DZ for halogen atoms (X = Cl, Br, I) and the 6-311 + G(d,p) basis set for all other atoms. In order to predict the specific site at which the pyrazole derivatives interact with halomethanes, local reactivity descriptors such as the Fukui functions were calculated. Detailed analysis of transition-state energies showed that alkylation occurred at the nitrogen atom N₂ in the pyrazole derivatives, in agreement with the chemical reactivity results. The reaction mechanisms were elucidated by performing intrinsic reaction coordinate (IRC) calculations that considered the effects of the solvent and the species of halogen in the halomethane.

Cooperative effects between π-hole triel and π-hole chalcogen bonds

MP2/aug-cc-pVTZ calculations have been performed on π-hole triel- and chalcogen-bonded complexes involving a heteroaromatic compound. These complexes are very stable with large interaction energy up to −47 kcal mol⁻¹. The sp²-hybridized nitrogen atom engages in a stronger π-hole bond than the sp-hybridized species although the former has smaller negative electrostatic potential. The sp²-hybridized oxygen atom in 1,4-benzoquinone is a weaker electron donor in the π-hole bond than the sp²-hybridized nitrogen atom. The π-hole triel bond is stronger than the π-hole chalcogen bond. A clear structural deformation is found for the triel or chalcogen donor molecule in these π-hole-bonded complexes. The triel bond exhibits partially covalent interaction, whereas the chalcogen bond exhibits covalent interaction in the SO₃ complexes of pyrazine and pyridine derivatives with a sp²-hybridized nitrogen atom. Intermolecular charge transfer (>0.2e) occurs to a considerable extent in these complexes. In ternary complexes involving an aromatic compound, wherein a triel bond and a chalcogen bond coexist, both the interactions are weakened or strengthened when the central aromatic molecule acts as a double Lewis base or plays a dual role of both a base and an acid. Both electrostatic and charge transfer effects have important contributions toward changes in the strength of both interactions.

MP2/aug-cc-pVTZ calculations have been performed on π-hole triel- and chalcogen-bonded complexes involving a heteroaromatic compound. Both interactions exhibit cooperative/diminutive effect, depending on the role of the central heteroaromatic compound.

Hydrogen bonds, and σ-hole and π-hole bonds – mechanisms protecting doublet and octet electron structures

For various interactions electron charge shifts try to protect the former doublet or octet electronic structure of the Lewis acid centre.

Dual functions of Lewis acid and base of Se in F2C=Se and their interplay in F 2CSe•••NH 3•••HX

High-level quantum chemical calculations of the ternary systems F2CSe∙∙∙NH3∙∙∙HX (X=BeH, BH2, OH, CN, OCH3, Cl, and F) and the corresponding binary systems have been carried out in view of geometries, vibrational frequencies, interaction energies, orbital interactions, and electron densities. The molecular electrostatic potentials of F2CSe demonstrate that the Se atom could play a dual role of Lewis acid and base to form a chalcogen bond with NH3 and a hydrogen bond or a covalent interaction with HX, respectively. The chalcogen bond can compete with the hydrogen bond for the complexes involving F2CSe, but the covalent interaction is far stronger than the chalcogen bond. In the ternary complexes, both types of interactions are strengthened by each other, characterized by a shorter binding distance, a larger electron density, and a stronger orbital interaction. The covalent interaction has a greater enhancing effect on the chalcogen bond than the hydrogen bond does, resulting in a prominent shortening of ~0.23 Å distance for the Se∙∙∙N distance in F2CSe∙∙∙NH3∙∙∙BH3. The enhancement of both interactions in the ternary complexes has been understood with the electrostatic potentials and orbital interactions. Graphical Abstract The dual functions of Lewis acid and base of Se in F2CSe are enhanced each other in the ternary complexes.

Influence of F and Se substitution on the structures, stabilities and nature of the complexes between F2CSe and HOX (X = F, Cl, Br, and I)

The complexes between F₂CSe and HOX have been investigated to unveil the influence of F and Se substitution.