Solution and solid-state characterization of europium and gadolinium Schiff base complexes and assessment of their potential as contrast agents in magnetic resonance imaging

Two lanthanide Schiff base macrocyclic complexes, LnAM(OAc){sub 2}Cl{center dot}4H{sub 2}O (Ln = Eu, Gd; HAM - HexaAzaMacrocycle = C{sub 22}H{sub 26}N{sub 6}), have been characterized in view of the potential of the Gd complex as a magnetic resonance imaging (MRI) contrast agent. The relaxivity of GdHAM(OAc){sub 2}Cl was measured at 300 and 20 MHz and is as high as that for the gadolinium aquo ion. The number of coordinated waters, q, was measured by comparison of the luminescent lifetimes of EuHAM(OAc){sub 2}Cl in H{sub 2}O and D{sub 2}O and found to be between three and four. The complex GdHAM(OAc){sub 2}Cl{center dot}4H{sub 2}O was characterized by single-crystal X-ray diffraction. The complex crystallizes in space group P{bar 1} with Z = 2, a = 10.032 (2) {angstrom}, b = 12.765 (2) {angstrom}, c = 13.668 (3) {angstrom}, {alpha} = 69.190{degree} (9){degree}, {beta} = 72.405{degree} (9){degree}, and {gamma} = 74.07{degree} (1){degree}.