Complex Formation of Chromium(III) Ion with Glycine in Alkaline Solution

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  • アルカリ性溶液でのグリシンとクロム(III)イオンの錯生成

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On the complex formation of chromium(III) ion with glycine it has recently been reported that glycinate is coordinated not only as a bidentate ligand but also as a unidentate through carboxylate ion. These investigations, however, have been carried out within weakly acidic or acidic media. The present paper is concerned with mainly the IR spectroscopic study on the structure of the chromium(II) complex in an alkaline solution where an excessive amount of glycine exists as ligand. The complex solution and the refernce solutions which included graded amounts of glycine were dried by lyophilizing and then IR absorption spectra of these solid residuals were measured by use of KBr pellet techniques. The measurement of IR absorption spectra of the complex itself, especially, the estimate for the number of moles of glycinate coordinated to one mole of chromium(M) was achieved by making use of the reference samples. The behavior of the complex on heating at 90 °C for 20 h was investigated by use of technique subtracting the IR spectra of the original complex (before heating) from those of the resulting complex. Simultaneously Van Slyke method and Kjeldahl method were applied to the estimate for the number of amino groups coordinated to chromium(III) ion.<BR>The following re sults have been obtained on the composition of the complex in the alkaline solution and the stability of the coordination bonds to heating.<BR>First, it was found that on the average, four of f ive glycinate ions are coordinated to chromium(III) as unidentate through carboxyhlate ion (Fig.5-B), and the remaining one is coordinated as bidentate (Fig.5-A).<BR>Secondly, it was proved that the coordination bond between chromium(III) ion and amino group in glycinate was almost entirely broken through heating at 90 °C for 20 h. However, the coordination bond between chromium(III) ion and carboxylate ion still remained unbroken as the unidentate ligand.<BR>Thirdly, it was found that by heating at 90 °C for 20 h the IR absotption bands due to carboxyl groups ‹CO2-› in glycinate ions forming chelate rings are shifted to the other wavenumber positions characteristic of carboxyl groups in glycinate ions coordinated to chromium(III) ion through the carboxylate ion as unidentate ligand, i. e. the absotption bands at 1650 cm-1 and 1380 cm-1 are shifted to 1600 cm-1 and 1400 cm-1 respectively after heating.

Journal

  • NIPPON KAGAKU KAISHI

    NIPPON KAGAKU KAISHI 1992 (11), 1326-1331, 1992-11-10

    The Chemical Society of Japan

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