New Dinuclear Mn III Compounds with 2‐MeC 6 H 4 COO and 2‐FC 6 H 4 COO Bridges – Effect of Terminal Monodentate Ligands (H 2 O, ClO 4 – and NO 3 – ) on the Magnetic Properties

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)