The gadolinium(III) chelate of 1-oxa-4,7,10-triazacyclododecane-4,7,10-triacetic acid. Formation of polymeric chains in the solid state and relaxivity properties

Abstract

The crystal structure of the gadolinium(III) chelate of the macrocyclic ligand odotra (1-oxa-4,7,10-triazacyclododecane-4,7,10-triacetate) was determined by X-ray single-crystal analysis: [Gd(odotra)(H 2 O) 5 ] crystallizes in the orthorhombic space group Pbca, with a = 12.84(8), b = 21.53(4), c = 15.30(7) A and Z = 8. The metal ion is at the centre of a square antiprism capped with one water molecule. The chelate units are linked by bridging carboxylic groups and form linear polymeric chains. The macrocycle adopts its preferred square [3333] conformation. Nuclear magnetic resonance dispersion studies indicate that [Gd(odotra)] and its analogue [Gd(dotra)] (dotra = 1,4,7,10-tetraazacyclododecane-4,7,10-triacetate) exhibit the same relaxivity behaviour but are not as effective magnetic resonance imaging contrast agents as expected presumably because of their low symmetry.