A μ1,1- or μ1,3-carboxylate bridge makes the difference in the magnetic properties of dinuclear MnII compounds

Abstract

Six new dinuclear Mn^II compounds with carboxylate bridges have been synthesized and characterized by X-ray diffraction: [{Mn(phen)₂}₂(μ-RC₆H₄COO)₂](ClO₄)₂ with R = 2-Cl (1), 2-CH₃ (2), 3-Cl (3), 3-CH₃ (4), 4-Cl (5) and 4-CH₃ (6). Compounds 1 and 2 show two μ_1,3-carboxylate bridges in a syn–anti mode while compounds 3–6 present a very uncommon coordination mode of the carboxylate ligand: the μ_1,1-bridge. The magnetic properties of these compounds are very sensitive to the bridging mode of the carboxylate ligands. While compounds 1 and 2 (μ_1,3-bridge) display antiferromagnetic interactions, with J values of −1.41 and −1.66 cm⁻¹, respectively, compounds 3–6 (μ_1,1-bridge) show ferromagnetic interactions, with J values of 1.01, 0.98, 1.04 and 1.06 cm⁻¹, respectively. It is worth noting that compounds 3–6 are the first of their class to be magnetically characterized. The EPR spectra at 4 K for compounds with antiferromagnetic coupling (1 and 2) are more complex than those for compounds with a ferromagnetic interaction (3–6). Quite good simulations can be obtained with the ZFS parameters of the Mn^II ion D_Mn ∼ 0.095 cm⁻¹ and E_Mn ∼ 0.025 cm⁻¹ for compounds 1 and 2 and D_Mn ∼ 0.060 cm⁻¹ and E_Mn ∼ 0.004 cm⁻¹ for compounds 3–6.