Rate and Equilibrium Data for the Complex Formation of Alkali Metal Ions with the Cryptand (2,2,1) in Methanol

Abstract

Abstract The dissociation rates of complexes between alkali metal ions and the macrobicyclic ligand 4,7,13,16,21‐pentaoxa‐1,10‐diazabicyclo‐(8,8,5)‐tricosane (cryptand‐(2,2,1)) have been studied in methanol by stopped‐flew experiments at various temperatures. The corresponding rates of formation were calculated using stability constants. Enthalpies and entropies of activation were compared with the corresponding quantities of complexation and discussed in terms of ionic size and ionic solvation. The specific dependence of decomplexation rate and stability constant on ionic radius [15] were found also for the corresponding enthalpies of activation and complexation, respectively, but the preference of Na + over K + is reversed. This fact together with the observation that the rate of dissociation of Na(2,2,1) + is enhanced by proton catalysis, led to the suggestion that the cavity radius of (2,2,1) lies between the ionic radii of Na + and K + .