Synthesis, structure, spectroscopic and magnetic properties of two copper(II) dimers containing pyridine-2-carbaldehyde thiosemicarbazonate (L), [{CuL(X)}2](X = Cl or Br)

Abstract

The compounds [{CuL(X)}₂](X = Cl 1 or Br 2, HL = pyridine-2-carbaldehyde thiosemicarbazone) have been synthesised and structurally characterized. Both crystallize in the triclinic space group P. For compound 1, a= 7.915(3), b= 8.262(5), c= 9.016(2)Å, α= 67.97(3), β= 92.26(2), γ= 71.33(4)°, Z= 2, R= 0.046, R′= 0.054. For 2, a= 7.617(1), b= 8.451(3), c= 8.966(2)Å, α= 68.50(2), β= 95.94(1), γ= 71.73(2)°, Z= 2, R=R′= 0.035. The copper(II) ions have square-pyramidal environments with the tridentate thiosemicarbazone ligands and the halide atoms in an equatorial position. The sulfur atom of the tridentate ligand acts as a bridging ligand occupying the apical position of the symmetric copper atom in the dimeric structure. Such a disposition of the sulfur bridges is very scarce. Q-Band ESR spectra of the two compounds show rhombic signals with g₁= 2.183, g₂= 2.053, g₃= 2.033 for 1 and g₁= 2.161, g₂= 2.057, g₃= 2.033 for 2. Magnetic measurements on 1 and 2 show antiferromagnetic couplings between the copper(II) cations through the sulfur bridges. The exchange parameter is J/k=–6.8K (–4.7 cm^–1). Magnetostructural correlations have been analysed by using extended Hückel molecular orbital calculations.