Cospatial σ-Hole and Lone Pair Interactions of Square-Pyramidal Pentavalent Halogen Compounds with π-Systems: A Quantum Mechanical Study

Mahmoud A A Ibrahim; Ossama A M Ahmed; Sabry El-Taher; Jabir H Al-Fahemi; Nayra A M Moussa; Hussein Moustafa

doi:10.1021/acsomega.0c05795

Cospatial σ-Hole and Lone Pair Interactions of Square-Pyramidal Pentavalent Halogen Compounds with π-Systems: A Quantum Mechanical Study

ACS Omega. 2021 Jan 25;6(4):3319-3329. doi: 10.1021/acsomega.0c05795. eCollection 2021 Feb 2.

Authors

Mahmoud A A Ibrahim¹, Ossama A M Ahmed^{1

2}, Sabry El-Taher², Jabir H Al-Fahemi³, Nayra A M Moussa¹, Hussein Moustafa²

Affiliations

¹ Chemistry Department, Faculty of Science, Minia University, Minia 61519, Egypt.
² Department of Chemistry, Faculty of Science, Cairo University, Giza 12613, Egypt.
³ Chemistry Department, Faculty of Applied Sciences, Umm Al-Qura University, Makkah 21955, Saudi Arabia.

Abstract

In the spirit of the mounting interest in noncovalent interactions, the present study was conducted to scrutinize a special type that simultaneously involved both σ-hole and lone pair (lp) interactions with aromatic π-systems. Square-pyramidal pentavalent halogen-containing molecules, including X-Cl-F₄, F-Y-F₄, and F-I-X₄ compounds (where X = F, Cl, Br, and I and Y = Cl, Br, and I) were employed as σ-hole/lp donors. On the other hand, benzene (BZN) and hexafluorobenzene (HFB) were chosen as electron-rich and electron-deficient aromatic π-systems, respectively. The investigation relied upon a variety of quantum chemical calculations that complement each other. The results showed that (i) the binding energy of the X-Y-F₄···BZN complexes increased (i.e., more negative) as the Y atom had a larger magnitude of σ-hole, contrary to the pattern of X-Y-F₄···HFB complexes; (ii) the interaction energies of X-Y-F₄···BZN complexes were dominated by both dispersion and electrostatic contributions, while dispersive interactions dominated X-Y-F4···HFB complexes; and (iii) the X₄ atoms in F-I-X₄···π-system complexes governed the interaction energy pattern: the larger the X₄ atoms were, the greater the interaction energies were, for the same π-system. The results had illuminating facets in regard to the rarely addressed cases of the σ-hole/lp contradictory scene.