Abstract
The synthetic versatility of ligands formed by coupling oxine units with m-xylylene has resulted in the self-assembly of three methoxido–bridged dinuclear copper(II) complexes with the formula, [CuOCH₃X]₂L1, X = Br⁻ (1), Cl⁻ (2), NO₃⁻ (3) and L1 = 1,3-bis(8-quinolyl-oxymethyl)benzene. The complexes are isostructural, showing distorted square pyramidal geometry for each copper(II) ion. The Cu-O-Cu bridging angle of approximately 104° in all three cases favours strong antiferromagnetic exchange coupling. The effect of the auxiliary ligand is observed in the gradation of magnetic and catalytic properties. Variable temperature magnetic susceptibility gives exchange coupling constants, J values, between −500 and −310 cm⁻¹, indicative of strong antiferromagnetic coupling involving the methoxido-bridged units with subtler effects due to the auxiliary ligands. EPR behaviour is consistent with a diamagnetic ground state arising from substantial antiferromagnetic coupling. DFT calculations provided theoretical validation with J values estimated between −565 and −400 cm⁻¹ for the three complexes, and revealed spin delocalization over the coordination spheres including the auxiliary ligands. Catalysis of catechol by the three complexes followed Michaelis-Menten kinetics and displayed relatively high turnover numbers (between 2.3 and 6.0 × 10² h⁻¹) in comparison with other alkoxido bridged dinuclear copper(II) complexes, thus making these complexes good functional mimics of the native enzyme with respect to magnetic and catalytic properties.