An unusual gadolinium ten-coordinated dimeric complex in the series of MRI contrast agents: Na[Gd(H2O)AAZTA] · 3H2O

The crystal structures of the ligand AAZTA (6-amino-6-methylperhydro-1,4-diazepine tetraacetic acid) and of its Gd complex Na[Gd(H2O)AAZTA] · 3H2O have been determined by X-ray diffraction. AAZTA crystallizes as zwitterion with two deprotonated carboxylate groups and two protonated tertiary nitrogen atoms. In the solid state the gadolinium complex is a centrosymmetric dimer with bicapped square antiprismatic coordination geometry.