Kinetic Studies of Complexation of Divalent Strontium, Barium, Lead, and Mercury Cations by Aqueous 15-Crown-5 and 18-Crown-6.

The rates of complexation-decomplexation of the 15-crown-5 1,4,7,10,13-pentaoxacyclopentadecane and 18-crown-6 1,4,7,10,13,16-hexaoxacyclooctadecane complexes of the aqueous cations Sr2, Ba2, Pb2, and Hg2 have been determined from ultrasonic absorption measurements covering the 15-205 MHz frequency range at 25 degree. As in the case of previously reported studies of complexation of monovalent cations by these crown ethers, the data have been fitted to a two-step mechanism. Diffusion has been ruled out as the rate limiting step in the complexation. Loss of coordinated water from the ions is proposed as the rate determining step. Author