The metal-organic framework, Fe2(dobpdc) (dobpdc4– = 4,4′-dioxidobiphenyl-3,3′-dicarboxylate), was found to be redox-active and undergo a topotactic oxidative insertion reaction with weakly coordinating anions to yield Fe2(dobpdc)Ax (0 &lt; x &lt; 2 and A– = tetraflurorborate, hexafluorophosphate, and bis-(trifluoromethylsulfonyl)imide). Bulk oxidation of the metal-organic framework, by chemical and electrochemical methods, confirmed the material conducts both anions and electrons upon generation of a FeII/III Robin-Day Class IIA mixed-valence state. A small, near linear, contraction in unit cell volume is observed with oxidation, consistent with Fe2(dobpdc)Ax existing as a single phase. The reversibility of the electrochemical oxidation reaction was confirmed by ex situ 57Fe Mössbauer spectroscopy, ex situ powder x-ray diffraction, and galvanostatic cycling experiments. Although the organic linker contains a redox-active quinoid functionality, further oxidation to Fe2(dobpdc)Ax (2 &lt; x &lt; 4) was not accessible. However, the reactive semiquinoid radical was isolable in the isostructural Mg2(dobpdc) phase. Finally, a prototype sodium half-cell was constructed and the material was cycled over 50 times with a maximal specific energy of 316 Wh/kg.

Dual−ion battery cathode via oxidative insertion of anions in a metal–organic framework

251st National Meeting (2016)

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