Type I–IV Halogen⋯Halogen Interactions: A Comparative Theoretical Study in Halobenzene⋯Halobenzene Homodimers

Abstract

In the current study, unexplored type IV halogen⋯halogen interaction was thoroughly elucidated, for the first time, and compared to the well-established types I–III interactions by means of the second-order Møller–Plesset (MP2) method. For this aim, the halobenzene⋯halobenzene homodimers (where halogen = Cl, Br, and I) were designed into four different types, parodying the considered interactions. From the energetic perspective, the preference of scouted homodimers was ascribed to type II interactions (i.e., highest binding energy), whereas the lowest binding energies were discerned in type III interactions. Generally, binding energies of the studied interactions were observed to decline with the decrease in the σ-hole size in the order, C6H5I⋯IC6H5 > C6H5Br⋯BrC6H5 > C6H5Cl⋯ClC6H5 homodimers and the reverse was noticed in the case of type IV interactions. Such peculiar observations were relevant to the ample contributions of negative-belt⋯negative-belt interactions within the C6H5Cl⋯ClC6H5 homodimer. Further, type IV torsional trans → cis interconversion of C6H5X⋯XC6H5 homodimers was investigated to quantify the π⋯π contributions into the total binding energies. Evidently, the energetic features illustrated the amelioration of the considered homodimers (i.e., more negative binding energy) along the prolonged scope of torsional trans → cis interconversion. In turn, these findings outlined the efficiency of the cis configuration over the trans analog. Generally, symmetry-adapted perturbation theory-based energy decomposition analysis (SAPT-EDA) demonstrated the predominance of all the scouted homodimers by the dispersion forces. The obtained results would be beneficial for the omnipresent studies relevant to the applications of halogen bonds in the fields of materials science and crystal engineering.

Does a halogen bond require positive potential on the acid and negative potential on the base?

“…For example, Ibrahim and coworkers showed that small negative interaction energies can be calculated when two molecules were oriented so that their positively charged σ or π-holes approached one another. 60,61 However, it is unclear if these geometries represented true minima as the orientations were rigidly enforced. SAPT partitioning offered small negative electrostatic components, consistent with the finding present above.…”

Sigma-Hole and Lone-Pair-Hole Site-Based Interactions of Seesaw Tetravalent Chalcogen-Bearing Molecules with Lewis Bases

“…Thus, the Lewis basicity effect was inspected by employing PoCs of −0.25 and −0.50 au on the SF 4 and SeF 4 monomers through three different sites, namely the σ- and lp-holes. In accordance, the enumerated stabilization energy ( E stabilization ) was quantified within the chalcogen σ- and lp-hole···PoC distance scope of 2.5–5.0 Å through a 0.1 Å step size using the following equation ,, E normals normalt normala normalb normali normall normali normalz normala normalt normali normalo normaln = E σ ‐ .25em normala normaln normald .25em normall normalp ‐ normalh normalo normall normale ‐ normalb normale normala normalr normali normaln normalg .25em normalm normalo normall normale normalc normalu normall normale · · · normalP normalo normalC − E σ ‐ .25em normala normaln normald .25em normall normalp ‐ normalh normalo normall normale ‐ normalb normale normala normalr normali normaln normalg .25em normalm normalo normall normale normalc normalu normall normale …”

“…To electrostatically investigate to what extent the SF 4 and SeF 4 molecules could favorably form chalcogen σ– − and lp–hole site-based interactions, the point-of-charge (PoC) approach was fulfilled. Thus, the Lewis basicity effect was inspected by employing PoCs of −0.25 and −0.50 au on the SF 4 and SeF 4 monomers through three different sites, namely the σ- and lp-holes.…”

Hetero-Halogen···Halogen Interactions

“…The highest stabilizing energy is obtained when the θ H and θ L angles are 180°and 90°respectively, which is followed by θ H = θ L = 90°. The trend is very similar to the homo-halogen••• halogen interactions reported by Ibrahim et al 53 It may be noted that, according to their calculation, the interaction energies for the Ph−Cl•••Cl−Ph and Ph−Br•••Br−Ph interactions with θ X = 180°and 90°geometry are −1.32 and −1.80 kcal/mol, respectively, at the MP2/aug-cc-pVDZ level of theory. The interaction for the θ H = 180°and θ L = 90°geometry is slightly more stabilizing compared to that for θ H = 90°and θ L = 180°in the case of Br•••Cl interactions.…”