Crystal Structure and Magnetic Properties of Trinuclear Transition Metal Complexes (Mn(II), Co(II), Ni(II) and Cu(II)) with Bridging Sulfonate-Functionalized 1,2,4-Triazole Derivatives

Here we present the synthesis, structure and magnetic properties of complexes of general formula (Mn)(Me(2)NH(2))(4)][Mn(3)(μ-L)(6)(H(2)O)(6)] and (Me(2)NH(2))(6)[M(3)(μ-L)(6)(H(2)O)(6)] (M = Co(II), Ni(II) and Cu(II)); L(−2) = 4-(1,2,4-triazol-4-yl) ethanedisulfonate). The trinuclear polyanions were isolated as dimethylammonium salts, and their crystal structures determined by single crystal and powder X-ray diffraction data. The polyanionic part of these salts have the same molecular structure, which consists of a linear array of metal(II) ions linked by triple N1-N2-triazole bridges. In turn, the composition and crystal packing of the Mn(II) salt differs from the rest of the complexes (with six dimethyl ammonia as countercations) in containing one Mn(+2) and four dimethyl ammonia as countercations. Magnetic data indicate dominant intramolecular antiferromagnetic interactions stabilizing a paramagnetic ground state. Susceptibility data have been successfully modeled with a simple isotropic Hamiltonian for a centrosymmetric linear trimer, H = −2J (S(1)S(2) + S(2)S(3)) with super-exchange parameters J = −0.4 K for Mn(II), −7.5 K for Ni(II) and −45 K for Cu(II) complex. The magnetic properties of these complexes and their easy processing opens unique possibilities for their incorporation as magnetic molecular probes into such hybrid materials as magnetic/conducting multifunctional materials or as dopant for organic conducting polymers.