The sodium salt of a tris(tridentate anion)gadolinium(III) complex: pentasodium bis[chelidamato(3-)][chelidamato(2-)]gadolinate(III) hexadecahydrate

The sodium salt of a complex anion formed between gadolinium(III) and three variously deprotonated chelidamic acid (4-hydroxypyridine-2,6-dicarboxylic acid) ligand moieties, assigned as Na-5[Gd(C7H2NO5)(2)(C7H3NO5)]. 16H(2)O, i.e. pentasodium (4-hydroxypyridine-2,6-dicarboxylate)bis(4-oxidopyridine- 2,6-dicarboxylate)gadolinium(III) hexadecahydrate, forms as colourless mono clinic crystals upon vapour diffusion of ethanol into its aqueous solution. The ligand moieties, assigned as two trianionic and one dianionic chelidam ate species, are all tridentate in the complex anion of tricapped trigonal prismatic donor-atom geometry. The geometry of the ligands and that of the primary coordination sphere is very similar to that of the analogous anioni c tris(ligand)-rare earth complexes of the pyridine-2,6-dicarbuxylate (dipi colinate) dianion.