Metal Organic Frameworks (MOFs) are 3-D porous coordination polymers built up poly-complexing organic ligands and inorganic cations. Although almost all cations of the periodic table are currently used to produce new MOFs (alkaline, alkaline earths, transition metals, 3p elements, rare earths…), iron deserves a special attention, notably because of its reversible redox activity (III/II), abundancy and very low toxicity, which are of great interest in various fields of applications, ranging from heterogeneous catalysis, electrochemical energy storage, gas separation to biomedicine (e.g. imaging, controlled drug release). Whereas the average structures of MOFs are typically determined by X-ray diffraction (powder or single crystal), local information gained from other techniques are of outmost importance to thoroughly decipher their structure and properties, notably at work. Among the available techniques, <sup>57</sup>Fe Mössbauer spectroscopy is obviously particularly well suited for the analysis of iron based MOFs, notably to identify the redox state, coordination sphere and surroundings (water, anions…)of iron cations in MOFs, among others. Jean-Marc developed this topic since the 90’s through a long lasting collaboration with French MOFs chemists, first initiated by Gérard Férey and pursued by his collaborators, including the present authors.  We will here present few examples of studies related to iron MOFs (synthesis of new crystalline phases, study of their redox activity, gas sorption and separation) and show how the combination of characterization tools (notably XRD and Mössbauer spectroscopy) is mandatory to achieve a proper description of the materials and their properties.

Insightful contribution of Mössbauer spectroscopy (and Jean-Marc!) to the field of iron metal organic frameworks (MOFs)

ACS Fall 2021

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