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

Abstract

The reaction of tris(2-pyridylmethyl)amine (TPyA)/N,N-bis(2-pyridylmethyl)-2-aminoethanol (bpaeOH), H2DHBN/Na2C2O4/NaN3 and Fe(II/III) ions in MeOH leads to the isolation of three iron(III) dimeric complexes, namely [(TPyA)(DHBN)FeIIIOFeIII(TPyA)(DHBN)]·2H2O (1), [(bpaeOH)(C2O4)FeIIIOFeIII(C2O4)(bpaeOH)]·2H2O (2) and [(TPyA)(N3)FeIIIOFeIII(N3)(TPyA)](ClO4)2 (3) (H2DHBN=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 (O2−) 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/kB=−112K (−78cm−1), θ=−0.29K, ρ=0.035; 2: g=2.0, J/kB=−141K (−98cm−1), θ=−0.3K, ρ=0.01; 3: g=2.0, J/kB=−130K (−90cm−1), θ=−0.5K, 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.