crystal structures and magnetic properties of two halogen bridged dinuclear copper(II) complexes [(4,4 0 -diethylester-2,2 0 -biquinoline) 2 Cu 2 (l-X) 2 X 2 ] (X À = Cl À , Br À) a b s t r a c t Two dinuclear Cu 2+ complexes, [(deebq) 2 Cu 2 (l-X) 2 X 2 ] (deebq = 4,4 0 -diethylester-2,2 0 -biquinoline, X À = Cl À for 1 and Br À for 2), were prepared and structurally characterized. The isostructural 1 and 2 crys-tallize in monoclinic space group P2 1 /c, with quite similar unit cell parameters and packing structures. Two Cu 2+ ions related to each other via an inversion center are connected by two halogen anions in a l 2 -bridge mode, and each Cu 2+ ion is coordinated by two N atoms form one deebq ligand and three X À anions to form distorted trigonal bipyramidal coordination geometry in dinuclear Cu 2+ complex. The neighboring dinuclear units are held together through intermolecular van der Waals forces. Two com-plexes show antiferromagnetic (AFM) coupling nature with J/k B = À73.4 K for 1 and À83.7 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.