Tuning the topologies of Co(II) and Ni(II) complexes with EDTA, 1,3-PDTA and 1,4-BDTA ligands: Synthesis and spectroscopic data of [Mg(H2O)6][Co(1,4-bdta)] · 3H2O and [Mg(H2O)6][Ni(1,4-bdta)] · 3H2O complexes, and the X-ray structure of their chiral cryst

The hexadentate complexes [Mg(H2O)6][Co(1,4-bdta)] · 3H2O (a) and [Mg(H2O)6][Ni(1,4-bdta)] · 3H2O (b) (where 1,4-bdta represents the 1,4-butanediaminetetraacetate ion) have been synthesized and characterized by electronic absorption spectroscopy and X-ray crystallography. The complexes (a) and (b) form isomorphic crystals that undergo a spontaneous resolution during the crystallization process yielding either enantiopure Λ (space group P61) or Δ (space group P65) isomers. The [M(1,4-bdta)]2− (M = Co(II) (a) and Ni(II) (b)) and [Mg(H2O)6]2+ octahedra are arranged in hydrogen bonded 2D-layers. Interception of these layers results in chiral channels filled with water molecules, which together with uncoordinated carboxylate oxygens of the complex anion, form mono-spiro chain that propagates in a helical manner along the c-direction. To the best of our knowledge, this is the first report on spontaneous resolution involving 1,4-bdta ligand and one of a few reports that concern conglomerate crystallization of M(II)(N2O4) complexes. The electronic absorption spectra of [Co(1,4-bdta)]2− and [Ni(1,4-bdta)]2− are presented and discussed in comparison with those of similar complexes and with reference to the varying topologies of these complexes.

Graphical abstractStereochemically labile hexadentate cobalt(II) and nickel(II) complexes with 1,4-bdta ligand, [Mg(H2O)6][Co(1,4-bdta)] · 3H2O (a) and [Mg(H2O)6][Ni(1,4-bdta)] · 3H2O (b), have been synthesized and characterized by UV–Vis spectroscopy and X-ray crystallography. These complexes have been shown to undergo a spontaneous resolution upon crystallization, an unprecedented instance with this type of ligand.Figure optionsDownload full-size imageDownload as PowerPoint slide