Cation-Activated Halogen Bonding: Experimental and Theoretical Study of The Enhancement of σ-Hole Potential Due to The Group 1 Elements Coordination

This combined experimental and theoretical study examines cation-mediated σ-hole electrostatic potential enhancement in a triethylene glycol derivative functionalized with 2,4,6-tribromophenol ligand system. DFT calculations reveal significant increase of electrostatic potential at bromine sites (up to 352 kJ/mol for Li⁺ coordination, representing a 4-fold enhancement over the free ligand’s potential of 87 kJ/mol). ¹H NMR shows weak Na⁺ binding (K²⁹⁸ = 1.03^–5 M^–1) in acetonitrile, highlighting strong solvent competition effects. The observed nonlinear activation trend (Li⁺ > K⁺ > Na⁺) contrasts with complete absence of the potential enhancement for H⁺, Rb⁺ and Cs⁺ complexes due to geometric constraints.