Structure and magnetic properties of polynuclear copper(II) compounds with syn–anti carboxylato- and bromo-bridges

Synthesis, spectroscopic and magnetic properties, and X-ray crystal structures of two copper(II) polymers Cu(2-qic)Br (2-qic = quinoline-2-carboxylate) (1) and Cu(2-pic)Br (2-pic = pyridine-2-carboxylate) (2) are described. These compounds are isostructural with Cu(2-qic)Cl and Cu(2-pic)Cl, respectively, the X-ray crystal structures of which were reported recently. Both complexes are polynuclear copper(II) compounds (1D and 2D, respectively) based on syn–anti carboxylate bridges and additionally on linear monobromo- (in 1) and dibromo-bridging (in 2) motifs. The magnetic properties were investigated in the temperature range 1.8–300 K. They reveal the occurrence of strong antiferromagnetic coupling (J1 = −102.5 cm−1) through the single bromo-bridge in 1, which is much stronger than that transmitted by the single chloro-bridge (J = −57.0 cm−1). Very weak ferromagnetic interaction through the syn–anti carboxylate bridge J2 is expected as it was observed in isomorphous Cu(2-qic)Cl (J = 0.37 cm−1). For 2 a weak ferromagnetic couplings through the syn–anti carboxylate (zJ′ = 1.35 cm−1) and dibromo-bridges (J = 8.31 cm−1) were found. The experimental results indicate that the observed ferromagnetic exchange through dibromo-bridge is weaker than that in the chloride analog (J = 15.0 cm−1). The magnitude of magnetic interactions is discussed on the basis of structural data of compounds 1 and 2 and their halide analogues.