Dual σ- and π-Hole Chalcogen Bonding with Cooperative π-Stacking: Noncovalent Forces That Amplify Halogen Bond Donors

This work presents a strategy for amplifying halogen bond donor capability through the cooperative interplay of dual σ- and π-hole chalcogen bonding and π···π stacking. Employing 4-nitro-5-chalcogenocyanatophthalonitriles as coformers for cocrystallization with haloarenes, we demonstrate an advanced approach that surpasses the previously utilized tetracyanobenzene methodology. The key novelty lies in the simultaneous manifestation of three cooperative noncovalent interactions (NCIs): Ch···Hal (Ch = S, Se) bonding, π···π stacking, and π-hole(C)···LP(Hal) interactions. The cooperative effect of these NCIs amplifies the electrostatic potential at halogen σ-holes (VS,max) up to 6.5-fold beyond unassociated haloarene and 1.5-fold beyond previously achievable levels, enabling weak halogen bond donors to function effectively. Comprehensive theoretical analysis (DFT/PBE0-D3/def2-TZVP for MEP; QTAIM analysis with B3LYP/def2-TZVP wave functions; NCI plots with s = 0.5 isovalue) through electrostatic potential mapping, quantum theory of atoms in molecules (QTAIM), and NCI index calculations confirms the cooperative nature of these interactions. Our findings open a route for the rational design of crystalline supramolecular systems where controlled modulation of NCIs is essential. π-Chalcogen bonding represents a valuable finding, as this interaction type remains a very rare phenomenon in supramolecular chemistry. The geometric distinction between π-hole (observed range: 87.3–92.8° in our structures) and σ-hole (164.2–167.1° in our structures) interactions provides unambiguous evidence for the coexistence of two fundamentally different bonding modes.