Synthesis, structures and magnetic properties of tetranuclear heterometallic complexes [Cu₃M] (M = Mn(II) Co(II) and Ni(II)) based on an oxamido-bridged ligand

Abstract

Three tetranuclear heterometallic coordination compounds of the general formula [(CuL)₂M(CuL·CH₃OH)](ClO₄)₂ [(M = Mn(for 2), Co(for 3) and Ni(for 4)] were synthesized by the reaction of the precursor CuL·0.5H₂O (1) (H₂L = 2,3-dioxo-5,6:13,14-dibenzo-7,12-diphenyl-1,4,8,11-tetraazacyclotetradeca-7,12-diene) with M(ClO₄)₂·6H₂O under solvothermal conditions. The compounds were fully characterized by elemental analysis, FTIR, UV–Vis spectroscopy, powder X-ray diffraction, single-crystal X-ray diffraction analysis. In addition, compound 2–4 were studied by magnetic susceptibility measurements. All three heterometallic compounds are isomorphous, and the central ions Mn(II), Co(II) and Ni(II) are connected to three CuL fragments via exo-cis oxamido bridges. Magnetic susceptibility studies of complexes 2–4 indicate the occurrence of antiferromagnetic coupling between the paramagnetic metals. The experimental data have been fitted according to the following Heisenberg Hamiltonian $\hat{H} = - 2J\hat{S}_{{\text{M}}} (\hat{S}_{{{\text{Cu}}1}} + \hat{S}_{{{\text{Cu}}2}} + \hat{S}_{{{\text{Cu}}3}} )$, leading to J = − 15.24 cm⁻¹, g_Cu = 2.06, g_Mn = 1.96 for complex 2, J = − 22.58 cm⁻¹, g_Cu = 2.1, g_Co = 2.55 for complex 3, and J = − 108.2 cm⁻¹, g_Cu = 2.09, g_Ni = 2.27 for complex 4, respectively.