Synthesis, structure, computational studies and magnetic properties of a ten-coordinate gadolinium(III) complex

An X-ray structural analysis of diaquabis [2,6-diacetylpyridinebis (p-nitrobenzoic hydrazide)] gadolinium(III) (Gd(DAPNBH)(2)), GdC46N14O14H30, FW=1160.07 g mol(-1), <P(1)over bar>, a=12.6116(9), b=13.8861(1), c=15.399(1) Angstrom, alpha=108.394(1), beta=90.305(1), gamma=103.665(1)degrees, V=2477.1(3) Angstrom(3), Z=2, revealed two pentadentate ligands coordinated to Gd with a coordination geometry intermediate between a bicapped square antiprism and a bicapped cube. Gd(DAPNBH)(2) has a relaxivity (R-1=8.2 mM(-1) s(-1)) three and a half times the relaxivity of GdDTPA (DTPA=diethylenetriamine pentaacetic acid), 2.3 mM(-1) s(-1), a commercial contrast agent.