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New complexanes. V. Complexes of ethylenediamine-N,N',α,α'-dipropionic acid and ethylenediamine-N,N'-α,α'-dipropionic-N,N'-diacetic acid with alkaline earth metal ions and certain other bivalent cations

J. Majer, M. Kotouček, and E. Dvořáková

Komenský University, Bratislava

 

Abstract: cf. preceding abstr. Complexes of the title compds., (I) and (II) resp., were studied under same conditions as in Part IV of this series. Stability consts. for the complexes of I and II, resp., are (M2+ and log KML given): Mg, 2.82, 8.58; Ca, 1.74, 10.01; Sr, --, 7.95; Ba, --, 6.66; Cu, 15.78, 18.69; Zn, 9.96, 16.02; Cd, 8.47, 15.92; Mn, 6.10, 13.30; Fe, 8.45, 14.18; Pb, 9.99, --. Dissocn. consts. are: pK1 6.59, pK2 9.48 for I and pK1 1.90, pK2 2.00, pK3 6.65, pK4 10.42 for II. Prepn. of I and II is described. Dissocn. consts. of I are higher than those of ethylenediamine-N,N-diacetic acid (III) which is caused by the higher basicity of N atoms due to the presence of Me group in α-position to the COOH group. Differences in stability consts. of complexes of I and III were small. Similarly, pK3 and pK4 values of II are higher than those of ethylenediaminetetraacetic acid (EDTA) but Cu, Cd, Zn, Mn, and Fe chelates of III are less stable than those of EDTA. This does not agree with the known relation between the ligand basicity and chelate stability. This discrepancy shows that the influence of the CH3 group on the chelate stability can be explained rather in terms of the steric configuration of chelate rings than in terms of N atoms basicity.

Full paper in Portable Document Format: 204a242.pdf (in Czech)

 

Chemical Papers 20 (4) 242–251 (1966)

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