Fe(4)(OAc)(10)[EMIM](2): Novel Iron-Based Acetate EMIM Ionic Compound

[Image: see text] We synthesized and characterized a novel iron(II) aceto EMIM coordination compound, which has a simplified empirical formula Fe(4)(OAc)(10)[EMIM](2), in two different hydration forms: as anhydrous monoclinic compound and triclinic dihydrate Fe(4)(OAc)(10)[EMIM](2)·2H(2)O. The dihydrate compound is isostructural with recently reported Mn(4)(OAc)(10)[EMIM](2)·2H(2)O, while the anhydrate is a superstructure of the Mn counterpart, suggesting the existence of solid solutions. Both new Fe compounds contain chains of Fe(2+) octahedrally coordinated exclusively by acetate groups. The EMIM moieties do not interact directly with the Fe(2+) and contribute to the structural framework of the compound through van der Waals forces and C–H···O hydrogen bonds with the acetate anions. The compounds have a melting temperature of ∼94 °C; therefore, they can be considered metal-containing ionic liquids. Differential thermal analysis indicates three endothermic transitions associated with melting, structural rearrangement in the molten state at about 157 °C, and finally, thermal decomposition of the Fe(4)(OAc)(10)[EMIM](2). Thermogravimetric analyses indicate an ∼72 wt % mass loss during the decomposition at 280–325 °C. The Fe(4)(OAc)(10)[EMIM](2) compounds have higher thermal stability than their Mn counterparts and [EMIM][OAc] but lower compared to iron(II) acetate. Temperature-programmed desorption coupled with mass spectrometry shows that the decomposition pathway of the Fe(4)(OAc)(10)[EMIM](2) involves four distinct regimes with peak temperatures at 88, 200, 267, and 345 °C. The main species observed in the decomposition of the compound are CH(3), H(2)O, N(2), CO, OC–CH(3), OH–CO, H(3)C–CO–CH(3), and H(3)C–O–CO–CH(3). Variable-temperature infrared vibrational spectroscopy indicates that the phase transition at 160–180 °C is associated with a reorientation of the acetate ions, which may lead to a lower interaction with the [EMIM](+) before the decomposition of the Fe(4)(OAc)(10)[EMIM](2) upon further heating. The Fe(4)(OAc)(10)[EMIM](2) compounds are porous, plausibly capable of accommodating other types of molecules.