Analogy to a Chinese knot in an ion-pair copper(II)–neodymium(III) complex based on a hexa­dentate Schiff base condensation product of 5-bromo­salicyl­aldehyde and glycyl­glycine

Self-assembly of CuCl₂, NdCl₃, 5-bromo­salicyl­aldehyde and glycylglycine yields the ion-pair copper(II)–neodymium(III) complex, poly[[deca­aqua­bis­[μ₃-2-({2-[(5-bromo-2-oxidoben­zylidene)­amino]­acetyl}­aza­nidyl)­acetato]­bis­[μ₂-2-({2-[(5-bromo-2-oxidobenzylidene)­amino]­acetyl}aza­nidyl)acetato]­tetra­cop­per(II)dineodymium(III)] bis­{[2-({2-[(5-bromo-2-oxido­ben­zylidene)­amino]­acetyl}­aza­nidyl)­acetato]cuprate(II)} tetra­deca­hydrate], {[Cu₄Nd₂(C₁₁H₈BrN₂O₄)₄(H₂O)₁₀][Cu(C₁₁H₈BrN₂O₄)]₂·14H₂O}_n. The anion is planar and mononuclear, showing an approximately square-planar coordination of the metal atom, while the cation is a hexa­nuclear centrosymmetric transition metal–lanthanide (Cu–Nd) heterometallic complex, with the independent copper cations in square-planar and square-pyramidal coordinations. The asymmetric unit com­prises one half of this cation, one anion and seven solvent water mol­ecules. The positions of the six metal centres in the cation reproduce a Chinese knot arrangement. The dipeptidic Schiff base releases three H atoms and can act as a tetra­dentate, a penta­dentate or a hexa­dentate ligand. Longer inter­actions between the penta­dentate ligands and the Jahn–Teller Cu^II cation link the hexa­nuclear aggregates into cationic chains in the [010] direction in which 14- and 22-membered subloops occur. Extensive hydrogen bonding in three dimensions involves both the coordinated and the solvent water mol­ecules.