Conductance study of 1 : 1 19-crown-6 complexes with various mono- and bivalent metal ions in water

Formation constants (K-ML) of 1 : 1 19-crown-6 (19C6) complexes with mono- (M+) and bivalent metal ions M2+ were determined in water at 25 OC by condu ctomecry. The KML value of 19C6 for M+ and M2+ decreases in the order Rbf 1 Kf > T1(+) > Na+ = Ag+ > Li+ approximate to Csf and Pb2+ > Ba2+ > Sr2+, Cd 2+, Ca2+, respectively. The selectivity for the neighboring alkali metal io ns in the periodic table is lower for 19C6 than for 18-crown-6 (18C6) excep t for the case of Rb+ and Cs+. The same is true for the alkaline earth meta l ions. Generally, the KML values of 19C6 with M2+ are greater than those w ith M+. For Na+ and the ions which are smaller in size than Na+ Li+, Ca2+, Cd2+, the KML value is larger for 19C6 than for 18C6, but the contrary hold s for all the other ions of larger sizes than Naf. The Limiting ionic molar conductivity (lambda(o)) of the 19C6-K+ complex in water at 25 OC was dete rmined to be 43. Although 19C6 is larger than 18C6, the 19C6-K+ complex is much more mobile in water than the 18C6-K+ complex.