Mixed-ligand ⁶⁸Ga complexes with tetradentate/monodentate NS₃/N ('4+1') coordination: Relation of structure with in vitro stability

Gallium forms complexes of the general formula [Ga(NS₃)NHR₂], where NS₃ is the tripodal ligand tris(2-mercaptoethyl) amine and secondary amines (NHR₂) are co-ligands. Structure determinations reveal trigonal-bipyramidal structure of the mononuclear species and the tendency of solvent-coordinated species [Ga(NS₃)solv] (solv: water, methanol) to condensate to trinuclear species. Challenge experiments with the plasma protein transferrin, performed with the respective Ga-68 complexes, show enhanced stability of the aminederived species [Ga(NS₃)NHR₂] with piperidine and imidazole derivatives as the most stable complexes.