Competition Between the Two σ‐Holes in the Formation of a Chalcogen Bond

Abstract

A chalcogen atom Y contains two separate σ-holes when in a R 1 YR 2 molecular bonding pattern. Quantum chemical calculations consider competition between these two σ-holes to engage in a chalcogen bond (ChB) with a NH 3 base. R groups considered include F, Br, I, and tert-butyl (tBu). Also examined is the situation where the Y lies within a chalcogenazole ring, where its neighbors are C and N. Both electron-withdrawing substituents R 1 and R 2 act cooperatively to deepen the two σ-holes, but the deeper of the two holes consistently lies opposite to the more electron-withdrawing group, and is also favored to form a stronger ChB. The formation of two simultaneous ChBs in a triad requires the Y atom to act as double electron acceptor, and so anti-cooperativity weakens each bond relative to the simple dyad. This effect is such that some of the shallower σ-holes are unable to form a ChB at all when a base occupies the other site.

Affinity of Telluronium Chalcogen Bond Donors for Lewis Bases in Solution: A Critical Experimental‐Theoretical Joint Study

“…Regardless of the σ‐hole(s) occupied by OPPh 3 in the 1 : 1 and 1 : 2 adducts considered here, it is found that the V max potential of any unoccupied σ‐hole decreases linearly with the occupation of the other sites: the association of one base with one σ‐hole decreases the V max potential of the two others by about 21 kcal mol −1 , and the association of a second base again decreases the V max potential of the remaining free σ‐hole by another 21 kcal mol −1 . Noteworthy, the plot of the Hammett σ m parameters [72] with the V max values of the σ‐holes of Te in di(3,5‐disubstituted‐aryl)methyltelluroniums ( 1 + – 6 + ; Figure S9) shows a non‐linear scattered correlation; [16,104, 105] the V max potential values of the three σ‐holes growing with Hammett‐Taft's [72] σ m values.…”

“…The inter-fragment correlation contribution can be further divided into charge transfer E ðX;YÞ CT;X!Y þ E ðX;YÞ CT;Y!X , dispersion E ðX;YÞ disp and triple excitations: E ðX;YÞ ðTÞ : about 21 kcal mol À 1 , and the association of a second base again decreases the V max potential of the remaining free σ-hole by another 21 kcal mol À 1 . Noteworthy, the plot of the Hammett σ m parameters [72] with the V max values of the σ-holes of Te in di(3,5disubstituted-aryl)methyltelluroniums (1 + -6 + ; Figure S9) shows a non-linear scattered correlation; [16,104,105] the V max potential values of the three σ-holes growing with Hammett-Taft's [72] σ m values.…”

“…[37] In these cases the 1 : 1 stoichiometry is reasonable considering that the first association through one σ-hole should weaken the other. [16] However, different stoichiometry can be expected with atoms bearing up to three σ-holes such as in neutral pnictogen(III) or cationic chalconium(IV) compounds. The binding properties of pnictogen-based species were studied in specific cases, [38] showing that PhSbCl 2 can bind two chloride anions.…”

Crystal Engineering, Electron Conduction, Molecular Recognition and Reactivity by Chalcogen Bonds in Tetracyanoquinodimethanes Fused with [1,2,5]Chalcogenadiazoles

“…Furthermore, the two-dimensional network structure formed by ChBs is key for the novel electric-field-controllable conductance switching of the BTDA-dimer 10 46 and for the mixed-valence semiconducting framework of BTDA ( 1 ), 47 both of which have been reported recently. Both the development of new members of the BTDA family 8e 48 and a better understanding of ChBs 8f 21 is expected to expand the chemistry of this attractive class of compounds.…”

Pd and Pt metal atoms as electron donors in σ-hole bonded complexes

“…33–39 Over the years, the investigations of these interactions have moved beyond halogen atoms, hence the development of analogous chalcogen or pnicogen bonds which engender robust study. 36,40–44…”