Synthesis and Magnetism of Ferromagnetically Coupled [Cu3IICrIII] Heterotetranuclear Complexes Bridged by Oxalate Groups

Abstract

Three novel μ-oxalato-bridged Cu3IICrIII-type heterotetranuclear complexes described by the overall formula [Cu3Cr(ox)3L3](ClO4)3, where ox represents the oxalato dianions, L stands for diaminoethane (en), 1,3-diaminopropane (pn), and 1,2-diaminopropane (ap) respectively, have been synthesized and characterized by elemental analyses, molar conductivity and magnetic moment (room-temperature) measurements, i.r., e.s.r. and electronic spectral studies. It is proposed that these complexes have oxalato-bridged structures consisting of three copper(II) ions and a chromium(III) ion, in which the chromium(III) ion has an octahedral environment and the three copper(II) ions have square-planar environments. Variable temperature magnetic susceptibility (4.2–300 K) measurements and studies of complexes [Cu3Cr(ox)3(en)3](ClO4)3(1) and [Cu3Cr(ox)3(pn)3](ClO4)3(2) revealed the occurrence of an intramolecular ferromagnetic interaction between the copper(II) and chromium(III) ions through the oxalato-bridge within each molecule. The magnetic data have been used also to deduce the indicated μ-oxalato-bridges [Cu3IICrIII] heterotetranuclear structure. On the basis of the spin Hamiltonian operator, \(\hat H = - 2J\left( {\hat S_{Cu_1 } \cdot \hat S_{Cr} } \right. + \hat S_{Cu_2 } \cdot \hat S_{Cr} + \hat S_{Cu_3 } \cdot \hat S_{Cr} ,\), the magnetic analyses were carried out for the two CuII—CrIII heterotetranuclear complexes and the spin-coupling constants (J) were evaluated as +6.36 cm−1 for (1) and +7.02 cm−1 for (2). The results indicate that the bridging oxalato entity should be able to transmit ferromagnetic interactions in the strict orthogonality [Cu3IICrIII] system.