Divergent noncovalent interactions of isomeric nitrile and isocyanide groups in selenodiazole–triazole cocrystals: σ-hole chalcogen bonding versus π–π stacking

Abstract

Herein, we report a comprehensive investigation of chalcogen bonding (ChB) selectivity between selenodiazole (SeDA) and functionalized 1,2,3-triazoles bearing both nitrile and isocyanide groups (1 and 2). Single-crystal X-ray diffraction analysis of cocrystals 1·SeDA and 2·SeDA reveals distinctly different binding preferences: isocyanide groups form conventional σ-hole chalcogen bonds Se⋯C with geometric parameters typical of directional ChB interactions; while nitrile groups engage preferentially in π–π stacking interactions with the selenodiazole ring system, avoiding direct Se⋯N contact. Comprehensive quantum chemical analysis employing QTAIM, IGMH, ETS–NOCV, NBO, and SAPT methods elucidates the electronic origins of this selectivity. The isocyanide–selenium interaction (−7.7 kcal mol⁻¹) exhibits significant charge transfer through LP(C) → σ*(Se–N) orbital interactions (50 me), with balanced electrostatic (46%), dispersion (32%), and induction (22%) contributions. In contrast, the nitrile–selenodiazole interaction (−10.9 kcal mol⁻¹) represents dispersion-dominated (59%) π–π stacking with minimal selenium orbital involvement and negligible charge transfer (<5 me). These findings establish electronic structure-based design principles for controlling supramolecular assembly patterns, demonstrating that hard–soft acid–base considerations extend to noncovalent interactions where softer carbon centers preferentially engage σ-holes, while harder nitrogen-containing systems favor delocalized π-interactions.