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

Abstract

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 CuIIcation 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.