A reduced electrophilicity for simple Lewis acids A involved in non-covalent interactions with Lewis bases B

Dissociation energies D_e for B⋯A = B + A can be written D_e = c'N_BE_A, where N_B and E_A are the nucleophilicities and electrophilicities of the Lewis base B and the Lewis acid A, respectively. A reduced electrophilicity is defined Ξ_A = E_A/σ_max, where σ_max is the maximum electrostatic surface potential on iso-surface of A, the atom directly involved in the non-covalent interaction. This definition is tested for halogen-bonded complexes B⋯YX, with Lewis bases B = N₂, CO, C₂H₂, C₂H₄, H₂S, HCN H₂O or NH₃. D_e plotted against N_B for several series B⋯YX yields straight lines of gradient E_A. When D_e/σ_max is the ordinate, the straight lines conflate to a single line, gradient Ξ_IX = E_IX/σ_max. Hydrogen-bonded complexes B⋯HX (X = F, Cl, Br, I), coinage-metal complexes B⋯MX (M = Cu, Ag, Au; X = F, Cl, Br, I), and alkali-metal bonded complexes B⋯MX (M = Li, Na: X = F, H, CH₃) behave similarly. Ξ_A is an intrinsic property of the atom immediately involved in the non-covalent bond.