Methoxo-bridged diiron(III) complex of m-xylylenebis(acetylacetonate) showing remarkable thermal stability for encapsulated dichloromethane

Abstract

The synthesis, structural characterization, spectroscopic, magnetic, electrochemical and thermal properties of a methoxo-bridged dinuclear iron(III) inclusion compound [Fe₂(m-xba)₂(µ-OCH₃)₂]·CH₂Cl₂ (1) derived from m-xylylenebis(acetylacetone) H2(m-xba) are reported. In 1, the symmetry related two distorted octahedral iron(III) centres are separated by 3.164(8) Å and the distance between the centroids of the aromatic ring planes is 11.836 Å. In the solid state molecular association takes place through C-H···O and C-H···Cl types of hydrogen bondings leading to the remarkable thermal stability of 1 whose desolvation takes place between 140 and 220 °C. The enthalpy change due to the loss of dichloromethane, as determined by differential scanning calorimetric measurement, is -103 kJ mol-1. Variable-temperature (4-300 K) magnetic susceptibility measurements indicated antiferromagnetic exchange interaction (H = -2JS₁S₂) in 1 with J = -13.5 cm^-1. The ¹H NMR spectrum of 1 in CD₂Cl₂ is consistent with its symmetric structure and exhibits maximum paramagnetic shift for the methoxy protons (ca. 200 ppm). The cyclic voltammogram of 1 in dichloromethane in the potential range 0 to -1.2 V exhibits a quasi-reversible redox couple due to Fe^IIIFe^III/Fe^IIIFe^II with E_1/2 = -0.85 V. Further reduction to the Fe^IIFe^II state at -1.5 V leads to decomposition of the complex species.