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 alpha-hydroxycarboxylates and one alpha-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)Cu-II(MA)] (1), [(BPCA)Cu-II(MPA)(H2O)] (2) and [(BPCA)Cu-II(BA)](n) (3), where BPCA = bis(2-pyridylcarbonyl)amidate, MA = racemic mandelate, MPA = racemic alpha-methoxy phenylacetate and BA = benzilate anion, shows the copper(II) ion in a distorted square-pyramidal geometry. In I the mandelate anion is coordinated to the copper(II) center in a bidentate fashion while in 2 the alpha-methoxycarboxylate is monodentate. In both cases a one-dimensional supramolecular array is formed through hydrogen bonds: the mononuclear units are directly connected in I 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 pi center dot center dot center dot pi stacking interactions between pyridines and one phenyl ring of benzilate anions are observed in the packing. (C) 2009 Elsevier Ltd. All rights reserved.