The free energy of cation binding into an aqueous complex is described well by an exponential function of ε HOMO (Figure A), the TBA + cation falls out of the trend, and a polynomial dependence is observed for G bind (ε LUMO ) (Figure ). The distance from the center of mass of the cation and water is reasonably well described by the exponential r 0 (ε HOMO ) and linear r 0 (ε LUMO ) functions (Figure ). Only the pyridinium derivatives (RPy + ) fall out of the r 0 (ε LUMO ) trend; the distance between the centers of mass for RPy + according to quantum chemical calculations is almost 1 Å longer than the obtained trend. The cause of this discrepancy may be greater asymmetry of RPy + compared to the other systems. The lowest binding energies and shortest distances are registered for the alkali metal cations, while the highest values are observed for the organic cations.