Transition between the Noncovalency and Covalency of σ–Hole Bonds

Abstract

The properties of the bond between a N-ligand and a Lewis acid containing a σ−hole are studied by quantum chemical methods. Interactions considered include pnicogen bonds involving SbX 5 , PX 5 , and PX 3 , where X represents any of the halogen atoms F, Cl, Br, or I. Also studied are the tetrel bonds of PbX 4 and SiX 4 , as well as the chalcogen bond involving TeOX 4 . Both NH 3 and NCH are applied as two possible bases of differing potency. Some of the bonds are very strong with interaction energies easily exceeding 25 kcal/mol and with AIM bond critical point densities much higher than 0.04 au, suggesting their classification as coordinate covalent bonds. The pentavalent SbX 5 and PX 5 fall into this category when combined with NH 3 , as does TeOX 4 . Although the tetrel bonds involving PbX 4 are only slightly weaker, they are probably better viewed as a strong noncovalent bond on the cusp of covalency. Changing the internal bonding of hypervalent SbX 5 to the more conventional SbX 3 weakens the interaction to a classical noncovalent pnicogen bond. Reducing the base nucleophilicity from NH 3 to NCH weakens the bonds so that they are clearly noncovalent.

The nature of π-hole spodium bonds in the HgLCl2(L = pyrrole, pyrazole, imidazole, pyridine, pyridazine, and pyrimidine) complexes: from noncovalent to covalent interactions

“…Moreover, lone pairs on the N/Te atom are also transferred to the empty 6 s orbital of the Hg atom in the complexes 4 ⋯NH 3 and 4 ⋯TeCH 2 . According to the study of σ-hole bonds, 62 the value of the Wiberg bond index (WBI) is 0.13 and 0.24 for a strong hydrogen and halogen bond in the ClH⋯NH 3 and FI⋯NH 3 complexes. For one of the strongest hydrogen bonds occurring in the HOHOH − system, the WBI reaches up to 0.38.…”

Pnictogen bond‐driven control of the molecular interaction between organophosphorus and acetylcholinesterase enzyme

“…As the nature of H-Bond is similar to other non-covalent interactions, we have applied the Popelier and Koch criteria to characterize molecular interactions. [54][55][56][57][58] Small positive values of r 2 ρ associated with high values of ρ indicate that a strong interaction is occurring. 59,60 For all four systems, the BPC i, which is the interaction pathway between the P and O exhibits a pronounced strength, with System 1 demonstrating the strongest interaction, followed by Systems 4, 2, and 3 in descending order of strength.…”