New insights into the comprehension of the magnetic properties of dinuclear MnIII compounds with the general formula [{MnL(NN)}2(μ-O)(μ-n-RC6H4COO)2]X2

Abstract

Five new dinuclear Mn(III) compounds with benzoato derivative bridges [{Mn(bpy)L}₂(μ-O)(μ-n-RC₆H₄COO)₂]X₂ (n-R = 3-MeO, 4-MeO and 4-tBu, X = NO₃⁻ and ClO₄⁻) were synthesised and characterised. According to X-ray diffraction, the X anions tend to be coordinated to the Mn ions and may occupy the place of the monodentate ligand L. Two structural isomers that only differ in one of their monodentate ligands have been obtained with the 3-MeOC₆H₄COO⁻ bridges. For all compounds, the Mn(III) ions display elongated octahedra with a pronounced rhombic distortion. To quantify these distortions separately, the elongation and rhombicity parameters Δ and ρ have been defined. The magnetic study shows a good relationship between the distortion of the coordination polyhedra and the zero field splitting parameters (D_Mn and E_Mn). From the magnetic data of a powder sample, it is possible to determine the sign and magnitude of D_Mn for ferromagnetic systems or weak antiferromagnetic systems with D_Mn < 0. For this kind of dinuclear compound, the R group at the meta position, the rhombic distortion of the octahedra, and large torsion angles between the Jahn–Teller axes lead to ferromagnetic interactions.