Structural Characterization of the Rhenium(V) Oxo Complex of Mercaptoacetyltriglyclne in its Dianionic Form

Dianionic [MO(MAG(3))](2-)(MAG(3) = penta-anionic form of mercaptoacetyltriglycine, M = (186)Re, (99m)Tc) complexes have important applications in nuclear medicine. In vivo the complexes have a deprotonated carboxyl group that is important to their biodistribution. The solid-state structures of (99)Tc and Re complexes with mercaptoacetyltriglycine reported previously are monoanions with protonated carboxyl groups. In the present work, we report the preparation and X-ray crystal structure of Na(2)[ReO(MAG(3))].5H(2)O (1), which contains the physiologically relevant dianion. The dianion is a distorted square pyramid with the nitrogen and sulphur donor atoms forming the base and the oxo ligand at the apex. The terminal carboxyl group is deprotonated, uncoordinated and has a syn orientation with respect to the oxo ligand. The syn conformation of the dianion in 1 differs in conformation from the anti-monoanion in [Bu(4)N][ReO(MAG(3)H)] but is similar to the syn-monoanion in [Ph(4)P][(99)TcO(MAG(3) H)].