Bulletin of the Chemical Society of Japan
Online ISSN : 1348-0634
Print ISSN : 0009-2673
ISSN-L : 0009-2673
Polarographic and Spectroscopic Studies on the Ion-pair Formation of Trioxalatocobaltate(III) Ions with Cations in Aqueous Solutions
Nobuyuki TanakaKazuo Koseki
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1968 Volume 41 Issue 9 Pages 2067-2072


The ion association between trioxalatocobaltate(III) anion and uni-, bi- and tervalent cations in aqueous solutions has been studied by polarographic and ultraviolet, visible and infrared spectroscopic methods. The association constants have been obtained by the measurement of the polarographic diffusion current of trioxalatocobaltate(III) ions in the presence of varied concentrations of cations at ionic strength 0.1 (NH4NO3) and 25°C. The influence of ammonium ion was taken into consideration in the treatment of polarographic data. The values obtained are 7.9 for (CH3)4N+[Co(ox)3]3−, 3.7±0.4 for (C2H5)4N+[Co(ox)3]3−, 22±1 for Na+[Co(ox)3]3−, 56±6 for Mg2+[Co-(ox)3]3−, 55±4 for Ca2+[Co(ox)3]3−, 53±3 for Sr2+[Co(ox)3]3−, 55±7 for Ba2+[Co(ox)3]3− and 118±17 for Al3+[Co(ox)3]3−. The association constant of NH4+[Co(ox)3]3− was determined by the conductivity measurement to be 33.6 (logK=1.53) at zero ionic strength. No change was observed in the visible, the ultraviolet and the infrared absorption spectra of trioxalatocobaltate (III) ions upon the addition of various cations even at the concentration at which the ion-pair formation is assumed to occur from the polarographic studies. These facts indicate that, in a sense of equilibrium study, there is no direct interaction between the complex anion and the cation, but one or more water molecules interpose between the two ions.

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