Stability constants of complexes of a series of metal cations with 6,7,9,10,17,18,20,21-octahydrodibenzo[b,k][1,4,7,10,13,16]hexa-oxa-cyclo-octadecin (dibenzo-18-crown-6) in aqueous solutions

Abstract

Aqueous stability constants for complex formation of dibenzo-18-crown-6 (dbc) with a series of metal ions have been determined spectrophotometrically by the solubility technique (Mⁿ⁺= Na⁺, K⁺, Rb⁺, Cs⁺, Ag⁺, Tl⁺, [NH₄]⁺, Sr²⁺, Ba²⁺, Pb²⁺, and La³⁺). The stability of the complexes is affected by changes in the ionic strength of the solutions and thermodynamic constants have been obtained by extrapolating the experimental values to infinite dilution. The monodissociated ion pairs [BaCl]⁺ and [SrCl]⁺ complex more strongly with dbc than the free ions Ba²⁺ and Sr²⁺. The behaviour of dbc with bivalent metal ions is much more sensitive to their ionic size than in the case of univalent ions. This is explained on the basis of electrostatic considerations.