Divalent metal complexes of meso- and dl-2,3-diaminobutane-N,N,N′,N′-tetra-acetic acid

Abstract

Stability constants of complexes of Mn, Cu(II), Zn, Cd and Hg(II) with meso- and dl- 2,3-diaminobutane-N,N,N′,N′-tetra acetic acid (DIMEDTA) valid for 20·0°C and μ = 0·1 M (KNO 3) have been obtained potentiometrically by a modification of Schwarzenbach's mercury-drop procedure adapted to continuous titration. In view of a discrepancy between the value thus found for the stability of the cadmium complex with the meso-isomer and that recently reported by Czech authors, a redetermination was made by the method of corresponding solutions using the cupric complex of meso-DIMEDTA as the coloured species. This procedure was first tested with the EDTA system and led to the value log K CdY = 16·76 ± 0·08 in fair agreement with the literature value. Differences in the stability of complexes with a particular metal and meso- or dl-DIMEDTA are explained on conformational grounds and discussed in relation to the stability of complexes with analogous ligands such as EDTA, PDTA and DCTA.