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

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.

On the Potentiality of X-T-X3 Compounds (T = C, Si, and Ge, and X = F, Cl, and Br) as Tetrel- and Halogen-Bond Donors

“…These results also accord with our earlier observations, which showed that the molecular stabilization energy was inversely correlated with σ-atom electronegativity and σ-atom•••PoC distance. 32,59 Regarding the results of the + σ-hole test, molecular stabilization energies decreased with increasing the atomic size of the interacted σ-atom and vanished for tetrels' interactions of the F-T-F 3 •••PoC systems. For the latter systems, at a T•••PoC distance of 2.5 Å, molecular destabilization energies were observed with values of 0.30, 5.12, and 6.68 kcal/mol for F-C- Interestingly, carbon-containing molecules showed more preferential molecular stabilization energies in the presence of positively charged PoC, compared to the negative one.…”

“…Groups IV–VII atoms have the ability to interact through their σ-holes as Lewis acid centers, with Lewis bases forming tetrel, − pnicogen, − chalcogen, − and halogen ,, bonds, respectively. It is now well established from several studies that the size and magnitude of the σ-hole relied basically on the electronegativity of the σ-atom and the electron-withdrawing power of the attached atoms/groups. − …”

Effect of External Electric Field on Tetrel Bonding Interactions in (FTF3···FH) Complexes (T = C, Si, Ge, and Sn)

“…Understanding noncovalent forces have been intensively grown in recent years due to their indispensable roles in versatile fields, including supramolecular chemistry, molecular recognition, and materials science. − Their role is also assumptive in biochemical processes, − reinforcing the connections between receptors and ligands that expedite protein transport and enzymatic catalysis. , More recent attention has been drawn among the scientific community toward giving a profound insight into the characterization of σ-hole interactions as one of the most predominant noncovalent interactions. The σ-hole concept was earlier announced − with a view for defining halogen-bonding phenomena, , then extended to include an immense family of noncovalent interactions where the group IV–VI elements interact as Lewis acid centers. − The σ-hole interactions’ occurrence was primarily ascribed to the existence of an area with lesser electron density compared to the surroundings and directly posed along the extension of the σ-bond. Indeed, the appellation of such interactions was previously settled based on the located position of the σ-hole-bonding donor of groups IV–VII in the periodic table as tetrel-, ,− pnicogen-, , chalcogen-, − and halogen-bonding − interactions, respectively.…”

σ-Hole and LP-Hole Interactions of Pnicogen···Pnicogen Homodimers under the External Electric Field Effect: A Quantum Mechanical Study

“…The nucleophilic and electrophilic natures of the chemical systems are accordingly addressed from an electrostatic perspective in terms of molecular stabilization energy. 33 The PoC approach has recently been notarized as a trustworthy method for studying the σ-hole, 94 − 96 lp-hole, 15 π-hole, 97 , 98 and R • -hole 99 interactions from an electrostatic point of view. 15 , 99 , 100 With the help of the PoC approach, the ability of the PCl 3 molecule to interact with Lewis bases and acids was investigated by employing negative and positive PoCs, respectively.…”