Copper(II) α-hydroxycarboxylate complexes of bis(2-pyridylcarbonyl)amine ligand: From mononuclear complex to one-dimensional coordination polymer

The coordination geometry and supramolecular structures of three copper(II) complexes of two α-hydroxycarboxylates and one α-methoxycarboxylate with nitrogen donor co-ligands are discussed. The complexes have been characterized by elemental analysis, ESI-MS, IR and electronic spectroscopy, thermogravimetric analysis and magnetic measurements. The X-ray structure analysis of all the complexes, namely [(BPCA)CuII(MA)] (1), [(BPCA)CuII(MPA)(H2O)] (2) and [(BPCA)CuII(BA)]n (3), where BPCA = bis(2-pyridylcarbonyl)amidate, MA = racemic mandelate, MPA = racemic α-methoxy phenylacetate and BA = benzilate anion, shows the copper(II) ion in a distorted square-pyramidal geometry. In 1 the mandelate anion is coordinated to the copper(II) center in a bidentate fashion while in 2 the α-methoxycarboxylate is monodentate. In both cases a one-dimensional supramolecular array is formed through hydrogen bonds: the mononuclear units are directly connected in 1 by the MA hydroxyl group, whereas in 2 is the coordinated water that operates as H donor towards the MPA carboxylate group and the BPCA carbonyl oxygens of nearby complexes. In 3 the benzilate anion, acting as bridging ligand between copper ions, gives rise to a one-dimensional coordination polymer. In the latter, intra- and inter-chain π⋯π stacking interactions between pyridines and one phenyl ring of benzilate anions are observed in the packing.

The supramolecular structures of copper(II) complexes with α-hydroxycarboxylate anions using nitrogen donor co-ligands are studied and compared with that obtained in the self-assembly of copper(II) with α-methoxycarboxylate. The results provide an insight about the role of these carboxylate species in stabilizing the supramolecular arrangement in solid state.Figure optionsDownload as PowerPoint slide