Syntheses and structures of two tetracopper(II) complexes with 2-hydroxy-5-methyl-1,3-benzenedicarboxaldehyde bis(benzohydrazone)

Abstract

The reaction of Cu(O2CCH3)2H2O and 2-hydroxy-5-methyl-1,3-benzenedicarboxaldehyde bis(benzohydrazone) (H3L) in methanol affords a tetranuclear complex of formula [Cu4(L)2(OCH3)2] (1). On the other hand, the reaction of Cu(ClO4)2·6H2O and H3L in presence of KOH in methanol affords 1 as minor product and a second solvated tetranuclear complex [Cu4(HL)2(OCH3)2(H2O)2](ClO4)2·2CH3OH·2H2O (2·2CH3OH·2H2O) as the major product. Both complexes were characterized by elemental analysis, magnetic, infrared spectroscopic and X-ray crystallographic measurements. The asymmetric unit of each complex contains a dinuclear unit which dimerizes and forms the tetranuclear complex. The two metal centres in the dinuclear unit are bridged through an endogenous phenolate-O and an exogenous methanolate-O. In 1, the dinuclear unit {Cu2(L)(OCH3)} dimerizes through two pairs of weak reciprocal equatorial-apical bridges involving one iminolate-O of L3- and the methanolate-O atoms, while the dinuclear unit {Cu2(HL)(OCH3)(H2O)}+ of 2 dimerizes through a similar pair of weak reciprocal equatorial-apical bridges involving only the methanolate-O atom. In these tetranuclear structures, each metal centre is in square-pyramidal NO4 coordination sphere. In the crystal lattice, a one-dimensional ordering of 1 occurs due to intermolecular π-π interactions, whereas 2·2CH3OH·2H2O forms a three-dimensional framework via intermolecular N-H···O, O-H···O, O-H···N hydrogen bonding and π-π interactions.