A μ(1,1)- or μ(1,3)-carboxylate bridge makes the difference in the magnetic properties of dinuclear Mn(II) compounds.

Six new dinuclear Mn(II) compounds with carboxylate bridges have been synthesized and characterized by X-ray diffraction: {Mn(phen)(2)}(2)(μ-RC(6)H(4)COO)(2)(2) with R = 2-Cl (1), 2-CH(3) (2), 3-Cl (3), 3-CH(3) (4), 4-Cl (5) and 4-CH(3) (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.