Synthesis, stability and nuclear magnetic resonance studies for the complexation of trivalent lanthanides, Ca 2, Cu 2 and Zn 2 by N,N′-bis (amide) derivatives of ethylenedinitrilotetraacetic acid

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Two N, N′- bis (amide) derivatives of H 4edta (ethylenedinitrilo- N, N′-diacetic acid), H 2L 1=bis ( iso-propylamide) and H 2L 2=bis ( tert-butylamide), were synthesized. Their protonation constants were determined by potentiometric titration in 0.10 mol dm −3 KCl and by NMR pH titration at 25.0±0.1°C. The stability constants of the complexes of calcium (II), copper (II), zinc (II), and gadolinium (III) with H 2L 1 and H 2L 2 were also investigated quantitatively by the potentiometric technique. The following stability constant sequence has been obtained: Gd 3>Cu 2>Zn 2>Ca 2 for the ligands H 2L 1 and H 2L 2. The proton NMR shift was measured for the complexes of Lu 3, Y 3 and Zn 2 with H 2L 1. These complexes are hexadentate, possibly of octahedral geometry and form various structural isomers. 17 O NMR shifts showed that the [DyL 1] + and [DyL 2] + complex had two to three inner-sphere water molecules. Water proton spin-lattice relaxation rates for the [GdL 1] + and [GdL 2] + complexes were also consistent with two inner-sphere gadolinium (III) coordination positions.