Strukturen zweier isomerer Gadolinium(III)-Polyaminopolycarboxylate -Argumente für signifikante Unterschiede ihrer 1 H-NMR-Relaxation/Structures of Two Isomeric Gadolinium(III) Polyamino Polycarboxylates -Relation to their Significant Differences in 1 H NMR Relaxation

We present preparation and X-ray crystal structures of gadolinium(III) complexes with two isomeric ligands; triethylenetetraminehexaacetic acid, H 6 ttha, and tris(2-aminoethyl)amine-hexaacetic acid, H 6 ttaha, respectively. In case of [C(NH 2 ) 3 ] 2 [Gd(Httha)] · 5 H 2 O (1) the inner coordination sphere is made up of 9 donor atoms of the ligand and reflects the low efficiency in accelerating 1 H NMR relaxation of an aqueous solution. In case of [C(NH 2 ) 3 ] 3 [Gd(ttaha)] · 3 H 2 O (2) the coordination number of 9 is realized via 7 donor atoms of the ligand and 2 oxygen atoms of a pending acetate group of the adjacent complex. Luminescence studies in aqueous solution confirm replacement of this acetate group by 2 water molecules. The relaxivity of [Gd(Httaha)] 2- is 7.3 ± 0.1 mM -1 s -1 as determined at pH = 7.2, 20 MHz and 40°C.