New Dinuclear MnIII Compounds with 2‐MeC6H4COO and 2‐FC6H4COO Bridges – Effect of Terminal Monodentate Ligands (H2O, ClO4– and NO3–) on the Magnetic Properties

Four new dinuclear MnIII complexes with the general formula [{Mn(bpy)L}(μ-RCOO)2(μ-O){Mn(bpy)L′}]n+ (bpy =2,2′-bipyridine) have been synthesized with RCOO = 2-MeC6H4COO (1, 2) and 2-FC6H4COO (3, 4); the counteranion could be NO3– (1, 3) or ClO4– (2, 4), and a monodentate ligand (L, L′) completes the octahedral environment of the manganese ions. For compound 1 L = H2O and L′ = H2O or NO3–; compound 2 shows two different dinuclear complexes, one of them with L = L′ = H2O and the other one with L = L′ = ClO4–; for compound 3, L and L′ = H2O or NO3– and for compound 4, L = H2O and L′ = ClO4–. The characterization by X-ray diffraction shows an important disorder in the crystal for the nitrate compounds, principally for compound 3, where each monodentate ligand could be a water molecule or a nitrate anion. The antiferromagnetic contribution to the magnetic coupling constant J is weaker for the nitrate compounds (1 and 3) than for the perchlorate compounds (2 and 4), and a ferromagnetic behaviour is found for compound 3, with J = +1.4 cm–1. The magnetic coupling constant found for compound 1 is J = –0.5 cm–1 and for compounds 2 and 4 it is –5.6 cm–1 and –3.5 cm–1, respectively. Extended Huckel calculations were carried out and there is evidence that the nitrate anions coordinated to the manganese atoms act as π-acid ligands providing a means to diminish the antiferromagnetic contribution.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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