Ultrasonic Absorption Study of the Complex Formation of Cadmium(II) Carboxylates in Aqueous Solution

Article abstract of DOI:10.1021/j100161a084

Ultrasonic absorption of aqueous cadmium(II) acetate, propionate, and n-butyrates has been measured with a pulse technique over a frequency range 3-260 MHz.The single relaxations observed in the metal-rich concentration regions are attributed to the complex formation of cadmium(II) carboxylates via the Eigen-Tamm mechanism of stepwise association.The reaction parameters are determined from the concentration dependences oh the relaxation frequency and amplitude.The association constant for outer-sphere complexing and the rate constant for ligand substitution lie in the range 0.91-1.14 and (4.1-5.4) * 10⁸ s^-1, respectively, both being almost independent of the nature of the carboxylate ions, in contrast to the zinc(II) carboxylates previously reported.The volume changes of the outer-sphere complexing and those of the ligand substitution are determined to be 1.7-2.4 and 4.6-6.7 cm³ mol^-1, respectively; these values are very different from those of cadmium(II) thiocyanate reported earlier.