Abstract
Four new dinuclear Mn^III^ 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‐MeC~6~H~4~COO (1, 2) and 2‐FC~6~H~4~COO (3, 4); the counteranion could be NO~3~^–^ (1, 3) or ClO~4~^–^ (2, 4), and a monodentate ligand (L, L′) completes the octahedral environment of the manganese ions. For compound 1 L = H~2~O and L′ = H~2~O or NO~3~^–^; compound 2 shows two different dinuclear complexes, one of them with L = L′ = H~2~O and the other one with L = L′ = ClO~4~^–^; for compound 3, L and L′ = H~2~O or NO~3~^–^ and for compound 4, L = H~2~O and L′ = ClO~4~^–^. 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 Hückel 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)