A new core topology in hexanuclear iron(III) carboxylate chemistry: [Fe6O3(O2CMe)9(OEt)2(bpy)2](ClO4)

Abstract

The structural, spectroscopic, and magnetochemical characteristics of a new hexanuclear iron-oxo complex are reported. [Fe₆O₃(O₂CMe)₉(OEt)₂(bpy)₂]ClO₄·¼EtOH·¼H₂O (3·¼EtOH·¼H₂O) crystallizes in the triclinic space group P with a = 11.524(1) Å, b = 15.865(2) Å, c = 17.029(2) Å, α = 65.92(1)°, β = 81.49(1)°, γ = 76.40(1)°, V = 2758 ų, and Z = 2. The [Fe₆O₃]¹²⁺ core of the cation contains an arrangement of six iron atoms not previously seen in iron-oxo compounds. In this arrangement, two [Fe₃O]⁷⁺ triangular units are bridged by a distorted tetrahedral oxide ion. ¹H- and ²H-NMR spectra are reported for two [Fe₆O₃]¹²⁺ complexes, 3 and the 4,4′-Me₂bpy analog 4, as well as CD₃CO₂⁻ and/or CD₃CD₂O⁻ derivatives of 3. Assignment of the resonances was made based on the ¹H-NMR chemical shift data and changes seen in the ¹H- and ²H-NMR spectra of the related deuterated complexes. The magnetic susceptibility of complex 3 was measured in the range of 5–300 K. The effective magnetic moment per molecule decreases gradually from 6.44 μ_B at 300 K to 3.31 μ_B at 70 K then more dramatically to 0.84 μ_B at 5 K, indicating a diamagnetic S = 0 ground state consistent with the expected presence of antiferromagnetic exchange interactions between the Fe^III ions.