Ion exchange of sodium or calcium in smectite clays with several diammonium cations was investigated in water, dimethyl sulfoxide (Me(2)SO), and acetonitrile (MeCN). Selectivity of adsorption to synthetic saponite was in the order : CH2(p-C(6)H(4)CH(2)N(+)Me(3))(2) (4) > p-C6H4(CH(2)N(+)Me(3))(2) (3) > (CH(2)CH(2)N(+)Me(3))(2))(2) (2) > (CH(2)N(+)Me(3))(2) (1) in water. In the competitive experiments, higher amounts of 4 were adsorbed than 1 in water whereas higher amounts of 1 were absorbed than 4 in Me(2)SO or MeCN. These results indicate that the solvation energy determines the selectivity of the ion exchange for these diammonium cations.