Ferromagnetic exchange coupling in a new bis(μ-chloro)-bridged copper(II) Schiff base complex: Synthesis, structure, magnetic properties and catalytic oxidation of cycloalkanes

A new (μ-chloro)-bridged complex [Cu(HL)Cl]2 · H2O (1) with the Schiff base ligand H2L, [2-((E)-(2-hydroxyethylimino)methyl)-4-bromophenol], has been synthesized and characterized by elemental analysis, IR, UV–Vis and EPR spectroscopic studies. X-ray diffraction studies show that 1 is a binuclear CuII complex with a pair of chlorine atoms bridging the copper atoms in a central Cu2Cl2 core. Each copper atom in 1 adopts a distorted square-pyramidal geometry with the imine nitrogen atom, alkoxy and phenoxy oxygen atoms from the Schiff base ligand and a bridging chlorine atom constructing the basal plane, while the apical position of the pyramid is occupied by the other bridging chlorine atom. Variable temperature susceptibility measurements show that complex 1 presents the highest ferromagnetic coupling [J = +43.2(5) cm−1] reported till date in any doubly chloro-bridged CuII dimer, and a weak interdimer antiferromagnetic coupling [J′ = -0.276(8) cm−1]. The complex also exhibits high catalytic activity towards the oxidation of hydrocarbons using H2O2 as terminal oxidant.

Graphical abstractA new doubly chloro-bridged complex [Cu(HL)Cl]2 · H2O (1) has been prepared using a ONO donor Schiff base ligand H2L, 2-((E)-(2-hydroxyethylimino)methyl)-4-bromophenol. Each copper(II) atom in the dimer is square-pyramidal having an axial–equatorial configuration of the bridging chlorine atoms. Temperature dependence of magnetic susceptibility measurements show a high ferromagnetic coupling between two copper(II) ions in 1 with J = +43.2(5) cm−1. The complex also exhibits efficient catalytic properties leading to the facile oxidation of cyclohexane and cycloheptane in presence of hydrogen peroxide as terminal oxidant.Figure optionsDownload full-size imageDownload as PowerPoint slide