Thiazolium Salts as Chalcogen Bond Donors

Abstract

The nitrogen atom is commonly considered to be the positive site in thiazolium cations. Counterintuitively, the shortest cation···anion contacts in thiazolium salts and their benzoderivatives involve the sulfur atom. The geometric features of these contacts allow for their rationalization as charge assisted chalcogen bonds (ChBs). Analyses of the Cambridge Structural Database and calculation of the surface electrostatic potential of benzo­[d]­thiazolium cations support this rationalization. The relevance and impact of the general tendency of thiazolium derivatives to function as ChB donors are exemplified by the ChBs as short as 87% of the sum of van der Waals radii of involved atoms in thiamine monophosphate, a key compound in human metabolism, and in two commonly used thiazolium organocatalysts.

Competition between chalcogen and halogen bonding assessed through isostructural species

“…Among the chalcogen atoms, as expected, the more polarizable Se atom showed a larger �-hole compared to the S atom. The areas of positive electrostatic potential were largely positioned directly opposite the C-Ch bond, but the �-hole closest to the arene ring contains an area of positive potential which has been overlapped with the positive potential of the C-H group, which is similar to what was observed recently for the benzothiazolium species (Konidaris et al, 2022).…”

σ-Hole Interactions Involving a Group 7 Metal: Close Contacts in Neutral and Anionic Rhenium Derivatives

“…A common criterion for characterizing noncovalent interactions is that the interatomic separation be less than the sum of the van der Waals radii of the respective atoms. Under this light, the normalized contact (Nc) is a useful tool to evaluate noncovalent interactions as it allows for a meaningful comparison of interactions involving different atomic species . In detail, the Nc for an interaction involving atoms i and j is the ratio D ij /( r vdw, i + r vdw, j ), where D ij is the experimental distance between i and j , and r vdw, i and r vdw, j are the van der Waals radii of i and j .…”

“…Under this light, the normalized contact (Nc) is a useful tool to evaluate noncovalent interactions as it allows for a meaningful comparison of interactions involving different atomic species. 35 In detail, the Nc for an interaction involving atoms i and j is the ratio D ij /(r vdw,i + r vdw,j ), where D ij is the experimental distance between i and j, and r vdw,i and r vdw,j are the van der Waals radii of i and j. The optimized Re 2a is 2.68 Å.…”

Benzothienoiodolium Cations Doubly Bonded to Anions via Halogen–Chalcogen and Halogen–Hydrogen Supramolecular Synthons

“…53 The binding by a halogen and a hydrogen atom 54−58 or by a chalcogen and a hydrogen atom 59−62 (heteroditopic XB/HB or ChB/HB supramolecular synthons, D 1 = halogen or chalcogen and D 2 = hydrogen in Figure 1c) was frequently observed. For instance, the XB/HB supramolecular synthon can be present in crystals of phenyliodonium salts (see onward), and recent examples of ChB/HB synthons embrace the structures of benzochalcogenazoles, 63,64 chalcogenadiazoles, 59,60,62 and palladium complexes featuring thiazol-2-amine ligands. 61 The homoditopic XB/XB and ChB/ ChB synthons have proved in the past years very useful in anion binding 51,52 and unconventional catalyses.…”