GADOLINIUM COMPLEXATION BY A NEW DTPA AMIDE LIGAND - AMIDE OXYGEN COORDINATION

A new type of neutral gadolinium complex with promise as an enhancement agent for magnetic resonance imaging has been prepared and characterized. The reaction of the bicyclic anhydride of diethylenetriaminepentaacetic acid (DTPA) with ethylamine gives the DTPA-bis(ethylamide) derivative DTPA-BEA (1) in 71% yield. The Gd(III) complex (2) was obtained in high yield from Gd2O3and the acid form of 1, and crystals were obtained from methanol solution. The most notable feature of the structure is coordination of the two amide carbonyl oxygen atoms to gadolinium. The gadolinium coordination polyhedron is a nine-coordinate tricapped trigonal prism with sites occupied by the three amine nitrogens, three carboxylate oxygens, two amide oxygens, and a water molecule. Amide coordinate bonds (Gd-O) average 2.39 Å versus a carboxylate (Gd-O) average of 2.36 Å, a Gd-N average of 2.70 Å, and water bond (Gd-O) of 2.42 Å. Crystal data: orthorhombic, Pbca (No. 61), a = 13.490 (2) Å,b= 18.436 (3) Å, c = 25.343 (3) Å, and Z = 8. Final residuals were R = 3.61% and Rw= 4.27% following full-matrix least-squares refinement of 3448 independent data with I > 0. © 1990, American Chemical Society. All rights reserved.