Electrochemical studies on alkali-metal complexes with the small macrocycle 1,4,7,10-tetraoxacyclododecane. Polarographic and potentiometric determination of the stability constants in propylene carbonate

Abstract

The electrochemical reduction of anhydrous alkali-metal perchlorates and of their complexes with 1,4,7,10- tetraoxacyclododecane (12-crown-4) has been investigated in propylene carbonate by normal polarography and potentiometry using a dilute amalgam pool electrode. Stability constants and stoicheiometries derived from partially irreversible polarographic waves corrected according to Gellings have been compared with potentiometric data. The ligand 12-crown-4 exhibits a high selectivity for Na⁺ which forms 1 : 2 complexes (log β₁= 3.5 ± 0.2, log β₂= 6.31 ± 0.04). The stability constants of the 1 : 1 adducts with Li⁺(log β₁= 2.93 ± 0.05), K⁺(2.15 ± 0.05), Rb⁺(1.69 ± 0.04), and Cs⁺(1.43 ± 0.05) decrease with increasing ionic radius of the encapsulated ion.