Potentiometric study of the mixed-metal complex formation of tetracarboxylate-18-crown-6 with aluminum and alkali and alkaline earth cations.
We give evidence for the formation of mixed-metal complexes of tetracarboxylate-18-crown-6 in the form of Al(3+)-macrocycle-M(Z+), with M(Z+) being an alkali or an alkaline earth cation. These binuclear systems are characterized by potentiometric p[H] titrations and the equilibrium constants for all major complexes formed are described. The results are presented in the form of distribution diagrams revealing the concentrations of individual complex species as a function of p[H]. The stability of the resulting mixed-metal complexes with Al(3+) and alkali and alkaline earth cations vary in the order Na(+)>K(+)>Cs(+) and Ca(2+)>Sr(2+)>Ba(2+). The complex behavior can be rationalized in terms of electrostatic interactions and direct coordination of the cations by the carboxylate groups from the crown ether periphery.
Tavakkoli
N
N
Department of Chemistry, Shiraz University, Shiraz, Iran.
Shamsipur
M
M