Lanthanide complexes of 2,2′‐oxydi­acetate: Na5[M(C4H4O5)3](BF4)2·6H2O (M = Nd,Sm or Gd)

The three title complexes, namely pentasodium tris(2,2′‐oxydi­acetato)­neodymium(III) bis­(tetra­fluoro­borate) hexahydrate and its samarium(III) and gadolinium(III) analogues, (I)–(III), respectively, are isomorphous and isostructural and have crystallographic D₃ symmetry. The lanthanide metal ions are nine‐coordinate, binding to three O atoms of three oxodi­acetate ligands. One Na⁺ ion is octahedrally coordinated to six O atoms and the other Na⁺ ion is octahedrally coordinated to four O atoms and two F atoms. The structure is effectively an infinite three‐dimensional polymer, consistent with the exceptional crystal quality. The racemic solutions spontaneously resolve on crystallization. For the individual crystals selected for structural analysis, the Nd and Sm complexes have the Λ configuration, while the Gd complex has the Δ configuration. The lanthanide–oxy­gen distances show the expected contraction of ca 0.02 Å with increasing atomic number for the lanthanide metal.