Syntheses, structures and magnetic properties of dinuclear oxo-bridged iron(III) complexes

The reaction of tris(2-pyridylmethyl)amine (TPyA)/N,N-bis(2-pyridylmethyl)- 2-aminoethanol (bpaeOH), H ₂DHBN/Na ₂C ₂O ₄/NaN ₃ and Fe(II/III) ions in MeOH leads to the isolation of three iron(III) dimeric complexes, namely [(TPyA)(DHBN)Fe ^IIIOFe ^III(TPyA)(DHBN)]·2H ₂O (1), [(bpaeOH)(C ₂O ₄)Fe ^IIIOFe ^III(C ₂O ₄)(bpaeOH)]·2H ₂O (2) and [(TPyA)(N ₃)Fe ^IIIOFe ^III(N ₃)(TPyA)] (ClO ₄) ₂ (3) (H ₂DHBN = 3,4- dihydroxybenzonitrile). These complexes have been investigated by single crystal X-ray diffractometry and magnetochemistry. Complexes 1-3 show dimeric structures with a bridging oxo (O ^2-) ion, and all the iron(III) ions have a distorted octahedral geometry. Complexes 1 and 3 have offset face-to-face π-π interactions between the dimers and possess a supramolecular structure, while 2 has O-H⋯O hydrogen bonding interactions between the dimers, which gives rise to a 1-D chain structure. These (μ-oxo)diiron(III) complexes exhibit antiferromagnetic interactions [1: g = 2.0, J/k _B = -112 K (-78 cm ^-1), θ = -0.29 K, ρ = 0.035; 2: g = 2.0, J/k _B = -141 K (-98 cm ^-1), θ = -0.3 K, ρ = 0.01; 3: g = 2.0, J/k _B = -130 K (-90 cm ^-1), θ = -0.5 K, ρ = 0.009]. These indicate that very strong antiferromagnetic interactions occur via the oxo bridge within the iron(III) dimer and weak antiferromagnetic interactions exist between the dimers.