Fig. 3.

Distance dependence of cation-π binding for sodium, potassium, ammonium, and NMe₄⁺ (one methyl down) ions. Binding energy is relative to the optimal binding, and distance is from the center of the benzene to Na⁺ or K⁺; N atom of ammonium; or methyl C of tetramethylammonium. Complexes with very short distances deviate from this electrostatic plot and were not included in the fitting.