Metal(II) Complexes of Ethylenediaminemonoacetic Acid (EDMA). Polarographic Studies of Cadmium(II) and Lead(II)-EDMA Complexes
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概要
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In the present paper, the d.c. polarographic behavior of cadmium(II) and lead(II) ions in ethylenediaminemonoacetate (EDMA) solutions was studied systematically. Since these metal(II) ions in an EDMA solution behave reversibly in a polarographic electrolysis, the compositions and the stability constants of cadmium(II)- and lead(II)-EDMA complexes could be estimated successfully from the shift of the half-wave potential of these metal(II) ions due to the complex formation with EDMA. The cadmium (II) ion was found to form complexes of 1-to-1 and 1-to-2 compositions with EDMA, and the electrode reaction mechanism was established to be:<BR>(<U>Remark: Graphics omitted.</U>)<BR>The successive formation constants of cadmium(II)-EDMA complexes, (<I>K</I><SUB>1</SUB>)<SUB>cdx</SUB> and (<I>K</I><SUB>2</SUB>)<SUB>cdx</SUB> were determined to be 3.01×10<SUP>8</SUP> and 5.65×10<SUP>4</SUP> respectively. On the other hand, the lead(II) ion forms only one complex with 1-to-l composition. In the presence of the chloride ion, the lead(II) ion was found to form a mixed ligand complex involving the chloride ion as well as a normal complex, PbX<SUP>+</SUP>, and the electrode reaction could be formulated as:<BR>(<U>Remark: Graphics omitted.</U>)<BR>The equilibrium constants, (<I>K</I><SUB>1</SUB>)<SUB>Pbx</SUB>(=[PbX<SUP>+</SUP>]/([Pb<SUP>2+</SUP>]·[[X<SUP>−</SUP>])) and <I>K</I><SUB>pbx</SUB><SUP>Cl</SUP>(=[PbXCl<SUP>0</SUP>]/([PbX<SUP>+</SUP>]·[Cl<SUP>−</SUP>])), were determined to be 1.69×10<SUP>8</SUP> and 1.01×10 respectively. The effect of the zinc(II) ion on the half-wave potential of the cadmium(II) ion in an EDMA solution was also studied. From the positive shift of the half-wave potential due to the presence of the zinc(II) ion, the formation constant of the zinc(II)-EDMA complex with a 1-to-1 composition was estimated to be 1.58×10<SUP>8</SUP>.
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