Conductometric Behavior of Univalent Cation-Podand Complexes in Methanol

摘要

The stability constants, log K of the 1 : 1 complexation for IA ions, Ag+, and Tl+ with a series of podands having different aromatic end-groups (グ-コ) have been determined conductometrically in methanol at 25.0 ∩. Exceptionally the equivalent conductivity, ルeq of Li+ and Na+ were increased by the addition of グ, because the complexed ions are less mobile than solvated ions. The order of log K values for グ was Ag+Tl+>K+>Na+>Rb+>Cs+>Li+. The log K sequence of the podands for the certain cations was グ>ケ>ゲ∶コ. And every podands except コ showed the maximum selectivity for Ag+ among the cations. These results were discussed in terms of the aromatic end-group effects, such as heterodonor atoms or conformational changes by ヰ -ヰ stacking interactions. The detailed conformations of ヰ-ヰ stacking were also discussed by the observations of upfield shifts of some aromatic protons upon complexation from 1H NMR spectra.