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 B E 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 = N 2 , CO, C 2 H 2 , C 2 H 4 , H 2 S, HCN H 2 O or NH 3 . 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, CH 3 ) behave similarly. Ξ A is an intrinsic property of the atom immediately involved in the non-covalent bond.