BEHAVIOR OF ALKALINE-EARTH METALS AND SILVER PERCHLORATES AND THEIR COMPLEXES WITH SOME CROWN ETHERS IN PROPYLENE CARBONATE

The conductance behaviour of magnesium, calcium, strontium, barium and silver perchlorates and their complexes with 18-crown-6 (18C6) and also, the complexing of magnesium and silver perchlorates with 15-crown-5 (15C5), dibenzo-18-crown-6 (DB18C6) and dicyclohexano-18-crown-6 (DCH18C6) have been studied in propylene carbonate (PC) at 25-degrees-C. In addition, a potentiometric study of complexes of silver perchlorate with these crown ethers was undertaken by using a silver indicator electrode in conjunction with a Hg/HgCl2(s) reference electrode in PC to compare the results with those obtained by conductance measurements, which were found to be in good agreement with each other. The complexation study indicates 1:1 complex formation between the metal ion and the crown ether. The order of the formation constant for 18C6 complexes is found to be: Mg2+ > Ca2+ > Sr2+ > Ba2+. The mobility of Mg2+ is found to be greater than those of 18C6-Mg2+, DB18C6-Mg2+ and DCH18C6-Mg2+, whereas it is lower than that of 15C5-Mg2+. The lambda-degrees values of Ca2+, Sr2+ and Ba2+ are somewhat lower than those of their respective 18C6 complexes, indicating that the moving entity of the metal ion is larger than that of its 18C6 complex in PC.