New dinuclear nickel(ii) and iron(ii) complexes with a macrocyclic ligand containing a N6S2 donor-set: Synthesis, structural, MALDI-TOF-MS, magnetic and spectroscopic studies

Abstract

A series of dinuclear Ni(II) and Fe(II) complexes with a Py₂N₄S₂ coordinating octadentate macrocyclic ligand L prepared by direct reactions have been studied. The overall geometry and bonding mode have been deduced on the basis of elemental analysis data, infrared, MALDI-TOF-MS, UV-vis spectroscopy, X-ray diffraction, conductivity and magnetic susceptibility measurements. In general both M²⁺ centres are sited into the macrocyclic cavity coordinated to a pyridinic nitrogen atom, one sulfur atom, two secondary amine groups from the macrocyclic backbone and completing the coordination spheres with two solvent or anionic molecules in a distorted octahedral geometry, except in the case of [Ni₂L(μ-Cl)(H₂O)₂](BF₄)₃·2H₂O, where the metal ions are sited in the macrocyclic cavity coordinated to a pyridinic nitrogen atom, one sulfur atom, two secondary amine groups from the macrocyclic backbone, one water molecule and one chloride ion acting as a bridge between the two centres in a distorted octahedral geometry. The magnetic properties of the nickel(II) complexes, [Ni₂L(CH₃CN)₄](BF₄)₄·3.5CH₃CN (11) and [Ni₂L(μ-Cl)(H₂O)₂](BF₄)₃·2H₂O (12) has been recorded in the solid state and indicates an unexpected ferromagnetic exchange in both cases, especially in compound 11 because no similar systems are previously reported in the literature presenting this magnetic behaviour. Further complexes with similar ligands are in progress to corroborate this unexpected ferromagnetic behaviour.