Syntheses, crystal structures and magnetic properties of two halogen bridged dinuclear copper(II) complexes [(4,4′-diethylester-2,2′-biquinoline)₂Cu₂(μ-X)₂X₂] (X^- = Cl^-, Br^-)

Two dinuclear Cu²⁺ complexes, [(deebq)₂Cu₂(μ-X)₂X₂] (deebq = 4,4′-diethylester-2,2′-biquinoline, X^- = Cl^- for 1 and Br^- for 2), were prepared and structurally characterized. The isostructural 1 and 2 crystallize in monoclinic space group P2₁/c, with quite similar unit cell parameters and packing structures. Two Cu²⁺ ions related to each other via an inversion center are connected by two halogen anions in a μ₂-bridge mode, and each Cu²⁺ ion is coordinated by two N atoms form one deebq ligand and three X^- anions to form distorted trigonal bipyramidal coordination geometry in dinuclear Cu²⁺ complex. The neighboring dinuclear units are held together through intermolecular van der Waals forces. Two complexes show antiferromagnetic (AFM) coupling nature with J/k_B = -73.4 K for 1 and -83.7 K for 2 within the dinuclear unit. The theoretical analyses utilizing broken-symmetry approach disclosed that the AFM coupling is achieved via orbital overlap in the dinuclear unit for two complexes.