SYNTHESIS, CHARACTERIZATION, AND CRYSTAL-STRUCTURES OF M(DO3A) (M = FE, GD) AND NA[M(DOTA)] (M = FE, Y, GD)

Macrocyclic amino carboxylate (DOTA and DO3A, where DOTA is 1,4,7,10-t etrakis(carboxymethyl)- 1,4,7,10-tetraazacyclododecane and DO3A is ris (carboxymethyl)-1,4,7,10-tetraazacyclododecane) complexes of Gd-(III) and Fe(III) have been synthesized, characterized, and evaluated for us e as potential contrast agents for magnetic resonance imaging (MRI). X -ray single-crystal analyses reveal four nitrogens and three oxygens c oordinated to the iron in both Na[Fe(DOTA)]-5H2O and Fe(DO3A).3H2O. No ne of the waters are coordinated to iron atoms; the former iron comple x has an uncoordinated carboxylate arm. Magnetic susceptibility and Mo ssbauer data confirm that both of the Fe(III) complexes are high spin (S = 5/2) compounds. Enneacoordination about the metal in the crystall ographically isostructural series Na[M(DOTA)(H2O)].4H2O (M = Gd, Y, Eu ) involves the four nitrogen atoms, an oxygen from each carboxyl arm, and one water molecule. Gd(DO3A) has been crystallized as a novel hydr ated complex [{Gd(DO3A)}3.Na2CO3].17H2O in which each enneacoordinate Gd atom is coordinated to the four nitrogens and an oxygen from each c arboxyl arm of the ligand, as well as two oxygens of the carbonate ion . No water molecule is coordinated to the Gd atoms in the crystal stru cture. The Gd(DO3A) and Gd(DOTA)-species are more effective water prot on relaxation agents than the Fe(III) chelates.