Transition metal ions and amides. VIII. Discrimination between different models for the complexation of Cu²⁺ with <i>N, N</i>′‐diglycyl 1, 2‐ethanediamine, N, N′‐diglycyl‐1, 3‐propanediamine and glycine ethylamide by potentiometric or by spectrophotometric titration

Abstract

Abstract The complexation of Cue 2+ with 1, 8‐diamino‐3, 6‐diaza‐2, 7‐octanedione ( N, N′ ‐diglycyl‐1, 2‐ethanediamine, DED) and with 1, 9‐diamino‐3, 7‐diaza‐2, 8nonanedione ( N, N′ ‐diglycyl‐1, 3‐propanediamine, DPD) has been studied by potentiometric and by spectrophotometric titration. With both ligands L the complexation to Cue 2+ leads to relatively complicated equilibria with CuLH 3+ , CuL 2+ , CuLH −2 , and dimeric Cu 2 L complexes. With DED, another dimeric species, Cu 2 L 2 H , is formed in addition. Independent numerical treatment of spectrophotometric and poteritiometric titrations was used to obtain a satisfactory model for the complexation and to test the relative discriminatory power of the two methods. Titrations of glycine ethylamide (GEA) were used as an additional test and as a model for DED and DPD. It was shown that in each case spectrophotometric titrations give results of similar reproducibility and have a discriminatory power equal to or better than potentiometric titrations, provided that optimum mathematical algorithms are used in the numerical treatment.