Transfer activity coefficients between water and methanol of complexes of some univalent and barium ions with dibenzocryptand 2.2.2, cryptand 2.2.2, and 18-crown-6

Abstract

Stability constants, K(f)LM(n+) (in which L = ligand and M(n+) = metal ion), of complexes of sodium, potassium, silver, thallium(I), and barium with dibenzocryptand 2.2.2 were determined at 25 degrees C in water and methanol. Also determined were transfer activity coefficients between methanol and water of two ligands, dibenzocryptand 2.2.2 and 18-crown-6. From these data, transfer activity coefficients of complexes of these two ligands with the above cations have been calculated. For univalent ion complexes of these ligands and, in addition, for such complexes of dibenzo-18-crown-6 and cryptand 2.2.2, the logarithms of the transfer activity coefficients are of the order of 2.5 units more positive than those of the ligands. Even though methanol is a good hydrogen bond donor, as is water, it is concluded that in methanol only the first solvation layer is built around an ether oxygen of the uncomplexed ligand as compared with several hydration layers in water. Hydrogen bonding to these ether oxygens when these ligands are complexed is greatly decreased as a result of ionic M(n+)-O bonding. Transfer activity coefficients of the barium complexes are found to be the same as those of the ligands. This is attributed to extensive solvation of LBa(2+).