Transition Metal Ions and Amides, VI. Complexation of the neutral and the anionic forms of 3, 7‐diazanonanedioic acid diamide and 3, 7‐diazanonanedioic acid diethylamide with Cu2+ and Ni2+

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Abstract
Two tetradentate ligands, 3, 7‐diazanonanedioic acid diamide (DANA) and 3, 7‐diazanonanedioic acid diethylamide (DANEA) have been synthesized and their complexes with Cu2+ and Ni2+ studied potentiometrically and spectrophotometrically. Three monomeric species, ML, MH−1L, and MH−2L, are formed. In ML, the two carbonyl oxygens are bound to the metal ions. Whilst Cu2+ gives complexes CuH−1DANA+ and CuH−1DANEA+ with one deprotonated amide group, the corresponding Ni2+ chelates do not exist in detectable concentrations. CuH−2DANA and NiH−2DANA are formed below pH 9. In the case of the diethyl derivative DANEA, however, steric interaction strongly hinders coordination of two deprotonated amide groups.