Synthesis, structure and valence-trapping vs. detrapping for new trinuclear iron pentafluoro benzoate complexes: possible recognition of organic molecules by 57Fe Mössbauer spectroscopy

Abstract

New mixed-valence trinuclear iron pentafluorobenzoate complexes were synthesized. Their valence-detrapping and/or valence-trapping phenomena were studied by ⁵⁷Fe Mössbauer spectroscopy and X-ray crystallography. For [Fe₃O(C₆F₅CO₂)₆(py)₃]·CH₂Cl₂ (1), a valence-trapped state was observed at low temperatures, while the valence-detrapped state was observed at room temperature. Removal of CH₂Cl₂ from 1 gives the de-solvated [Fe₃O(C₆F₅CO₂)₆(py)₃] (2) where the valence was trapped at room temperature. The CH₂Cl₂-free 2 can reversibly absorb and desorb CH₃CN; the process was followed by ⁵⁷Fe Mössbauer spectroscopy by monitoring valence-trapping and valence-detrapping phenomena. Organic molecules such as benzene, toluene, ethylbenzene, cumene, and xylene are also trapped by 2 and affect the iron valence states. However, small molecules such as H₂O and CO₂ do not affect the valence-trapped state of 2. Three xylene isomers trapped within the nano-void of 2 were distinguished by ⁵⁷Fe Mössbauer spectroscopy at room temperature.