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

The synthesis, structural characterization, spectroscopic, magnetic, electrochemical and thermal properties of a methoxo-bridged dinuclear iron(III) inclusion compound [Fe-2(m-xba)(2)(mu-OCH3)(2)]center dot CH2Cl2 (1) derived from m-xylylenebis(acetylacetone) H-2(m-xba) are reported. In 1, the symmetry related two distorted octahedral iron(III) centres are separated by 3.164(8) angstrom and the distance between the centroids of the aromatic ring planes is 11.836 angstrom. In the solid state molecular association takes place through C-H center dot center dot center dot O and C-H center dot center dot center dot Cl types of hydrogen bondings leading to the remarkable thermal stability of 1 whose desolvation takes place between 140 and 220 degrees 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 = -2JS(1)S(2)) in 1 with J = -13.5 cm(-1). The H-1 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 (FeFeIII)-Fe-III/(FeFeII)-Fe-III with E-1/2 = -0.85 V. Further reduction to the (FeFeII)-Fe-II state at -1.5 V leads to decomposition of the complex species.