Synthesis and ferromagnetic interaction in oxamido-bridged copper(II)-chromium(III) heterotetranuclear complexes

Two new mu-oxamido-bridged copper(II)-chromium(III) heterotetranuclear complexes formulated as [Cu-3(dmoxa)(3)Cr](ClO4)(3) (1) and [Cu-3(dmoxpn)(3)Cr](ClO4)(3) (2), where dmoxae and dmoxpn represent N,N'-bis[2-(dimethylamino)ethyl]oxamido and N,N'-bis[3-(dimethylamino)propyl]oxamido dianions, respectively, have been synthesized and characterized by the elemental analyses, spectroscopic (IR, UV, ESR) studies, magnetic moments (at room-temperature) and by molar conductivity measurements. It is proposed that these complexes have oxamido-bridged structures consisting of three copper(H) ions and a chromium(III) ion, in which the chromium(III) ion has an octahedral environment and the three copper(H) ions have a square-planar environment. The two heterotetranuclear complexes were further characterized by variable-temperature magnetization (3 similar to 300 K) measurements and the magnetic data have been used to deduce the indicated heterotetranuclear structure. The results derived from least-squares fit of the experimental data have confirmed that the operation of a ferromagnetic interaction between the adjacent copper(H) and chromium(III) ions occurs through the oxamidoridge within each molecule. On the basis of the spin Hamiltonian operator, H = -2J(S-Cu1.S-Cr +(SCu2SCr)-S-. + (SCu3SCr)-S-.), the magnetic analyses were carried out for the two copper(It)-chromium(III) heterotetranuclear complexes and the spin-coupling constants (J) were evaluated as +9.28 cm(-1) for (1) and +9.63 cm(-1) for (2). The influence of the symmetry of the magnetic orbitals on the nature of the magnetic interaction between the paramagnetic centers is preliminary discussed.