Biomimetic O(2) adsorption in an iron metal–organic framework for air separation

Bio-inspired motifs for gas binding and small molecule activation can be used to design more selective adsorbents for gas separation applications. Here, we report an iron metal–organic framework, Fe-BTTri (Fe(3)[(Fe(4)Cl)(3)(BTTri)(8)](2)·18CH(3)OH, H(3)BTTri = 1,3,5-tris(1H-1,2,3-triazol-5-yl)benzene), that binds O(2) in a manner similar to hemoglobin and therefore results in highly selective O(2) binding. As confirmed by gas adsorption studies and Mössbauer and infrared spectroscopy data, the exposed iron sites in the framework reversibly adsorb substantial amounts of O(2) at low temperatures by converting between high-spin, square-pyramidal Fe(ii) centers in the activated material to low-spin, octahedral Fe(iii)–superoxide sites upon gas binding. This change in both oxidation state and spin state observed in Fe-BTTri leads to selective and readily reversible O(2) binding, with the highest reported O(2)/N(2) selectivity for any iron-based framework.