Chalcogen Bonding "2S-2N Squares" versus Competing Interactions: Exploring the Recognition Properties of Sulfur

Chalcogen bonding (CB) is the focus of increased attention for its applications in medicinal chemistry, materials science, and crystal engineering. However, the origin of sulfur's recognition properties remains controversial, and experimental evidence for supporting theories is still emerging. Here, a comprehensive evaluation of sulfur CB interactions is presented by investigating 2,1,3-benzothiadiazole X-ray crystallographic structures gathered from the Cambridge Structure Database (CSD), Protein Data Bank (PDB), and own laboratory findings. Through the systematic analysis of substituent effects on a subset library of over thirty benzothiadiazole derivatives, the competing interactions have been categorized into four main classes, namely 2S-2N CB square, halogen bonding (XB), S⋅⋅⋅S, and hydrogen-bonding (HB). A geometric model is employed to characterize the 2S-2N CB square motifs and discuss the role of electrostatic, dipole, and orbital contributions toward the interaction.