Highly selective crystallization of metal(II) ions with 1,3-pdta ligand: Syntheses and crystal structures of the [Mg(H2O)6][Cd(1,3-pdta)(H2O)] · 2H2O and two isomorphic [Zn(1,3-pdta)]2− complexes

Abstract Three new hexadentate complexes: [Mg(H 2 O) 6 ][Zn(1,3-pdta)] · 2H 2 O ( 1 ), [Zn(H 2 O) 6 ][Zn(1,3-pdta)] · 2H 2 O ( 2 ) and [Mg(H 2 O) 6 ][Cd(1,3-pdta)(H 2 O)] · 2H 2 O ( 3 ) (where 1,3-pdta represents the 1,3-propanediaminetetraacetate ion) have been synthesized and characterized. The structures of 1 , 2 and 3 have been determined by X-ray crystallography. The complexes 1 and 2 crystallize in the space group Pnna of the orthorhombic crystal system and their crystals are isomorphic with those of other 1,3-pdta complexes containing metal(II) ions of the ionic radii of about 0.8–0.9 A. The complex 3 crystallizes in the space group Pbcn of the orthorhombic crystal system and its crystals are isomorphic with those of [Mg(H 2 O) 6 ][Mn(edta)(H 2 O)] · 2H 2 O (where edta is the ethylenediaminetetraacetate ion). The structural units of 1 and 2 consist of discrete [Zn(1,3-pdta)] 2− and [M II (H 2 O) 6 ] 2+ (M(II) = Mg ( 1 ) or Zn ( 2 )) octahedra, and two water solvent molecules all of which lie on a twofold axis of symmetry. The structural unit of 3 consists of discrete complex ions: [Cd(1,3-pdta)(H 2 O)] 2− and [Mg(H 2 O) 6 ] 2+ which are situated on twofold axis of symmetry and inversion centre, respectively, and two symmetry related water solvent molecules. The coordination polyhedron formed around Cd(II) is distorted pentagonal bipyramid. In contrast to crystals 1 and 2 in which the complex cations and anions alternate, each being octahedrally surrounded by the counter ions, a layered arrangement of cationic and anionic species is observed in 3 .