2-Pyridyl ketone oximes in iron(III) carboxylate chemistry: Synthesis, structural and physical studies of tetranuclear clusters containing the [Fe 4( μ3-O) 2] 8+ ‘butterfly’ core

Abstract

The use of 2-pyridyl ketone oximes, pyC(R)NOH (R = H, Me), in iron(III) carboxylate chemistry yielded the tetranuclear complexes [Fe 4O 2Cl 2(O 2CPh) 2{pyC(R)NO} 4] (R = H, 1; R = Me, 2). The crystal structure of 2 revealed the presence of a central [Fe 4( μ 3-O) 2] 8+ core comprising four Fe III ions in a ‘butterfly’ disposition and two μ 3-O 2− ions, each bridging three Fe III ions forming the ‘wings’ of the ‘butterfly’. The Mössbauer spectra from polycrystalline samples of 2 consist of composite quadrupole-split doublets, with parameters typical for high-spin iron(III) in octahedral environments. Magnetic susceptibility measurements on 2 revealed antiferromagnetic interactions between the S = 5/2 ferric ions; fits to the data required the use of two different parameters for the wingtip–body interactions. The best-fit values for these interactions were J 1 = −85 cm −1 and J 2 = −27 cm −1 (-2 J ijS iS j Hamiltonian formalism) resulting to a diamagnetic ground state.