Crystal Structures and Magnetic Properties of Newly Synthesized Mono- and Dinuclear Cu-II Schiff-Base Complexes

Abstract

Five Cu-II Schiff-base complexes, three mononuclear {[Cu(rslysH)center dot{H2O)(2)]center dot 2H(2)O center dot ClO4 (1); [Cu(rslysH)Cl] (2); [Cu(slysH)(H2O)Cl] (3) rslys and slys = 6-amino-2-[(2-hydroxybenzylidene)amino]hexanoate} and two dinuclear {[Cu-2(rslysH)(2)(CH3OH)(2)]center dot(H2O)(2)(NO3)(2) (4); [Cu-2(slysH)(2)(NO3)(2)]center dot(H2O)(3) (5)}, are reported herein. These complexes have been synthesized via a facile "one-pot" method in which the D/L- and L-lysine Schiff-base ligands are generated in situ. Various spectroscopic techniques and single-crystal X-ray diffraction were used in compound characterization. The X-ray diffraction studies revealed that complexes 1-3 are mononuclear; further, 4 and 5 are dinuclear in which two Cu-II centers are phenolate-bridged. Complexes 1, 2 and 3 are structurally similar, according to the nuclearity and the coordination environment around the metal center involving a tridentate D- or L-lysine-derived Schiff-base ligand. But the crystallographic packing is different, owing to the different counterions and number of solvent molecules present in the crystals. Compounds 1 and 2 are racemic due to the co-existence of chiral D- and L-lysine-based Schiff-base ligands. These copper(II) complexes give 2-D hydrogen-bonded networks and are racemic overall. Compound 3 is chiral, containing only the L-lysine-derived ligand in which a cylindrical 1-D hydrogen-bonded structure is observed in the solid state. Both 4 (achiral) and 5 (chiral) reveal 3-D hydrogen-bonded networks. A strong antiferromagnetic coupling interaction was observed by variable-temperature magnetic susceptibility measurements; this interaction is likely mediated through the phenolate bridge between the two Cu-II centers in 4 and 5.