Syntheses of new 15-membered and 16-membered macrocyclic ligands with three pendant acetato groups and the structures of the gadolinium(III) complexes

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Abstract

A condensation of diethylenetriaminepentaacetic dianhydride with ethylenediamine gave a 15-membered macrocyclic ligand with three pendant acetato groups, (15-dtpa-en)H3C10H18N5O2(CH2CO2H)3; a l6-membered analogue, (l6-dtpa-pn)H3 C11H20N5O2(CH2CO2H)3, was obtained by the use of propanediamine instead of ethylenediamine. The structures of their gadolinium(III) complexes, Gd2(15-dtpa-en)2·16H2O and Gd(16-dtpa-pn)·4H2O, were determined by X-ray analyses. Gd2(15-dtpa-en)2·16H2O crystallized in the orthorhombic space group Pbca with: a=18.205(1), b=18.930(1) and c=15.609(1) Å. Two Gd(III) ions are located between two ligand molecules, forming a binuclear metal chelate molecule with a center of inversion. The coordination geometry around a metal ion is described as a distorted tricapped trigonal prism that consists of nine coordinated atoms. Gd(l6- dtpa-pn)·4H2O crystallized in the monoclinic space group P21/c with: a =8.246(2), b = 14.995(3), c= 19.367(4) Å and β = 90.258(2)°. In this compound, a water molecule and a single ligand molecule are coordinated to a Gd(III) ion, forming a mononuclear chelate with a tricapped trigonal prism. The structural differences between the two Gd(III) complexes are a result of the differences in the favorable conformations assumed by the two macrocyclic ligands.

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