Two distinct redox intercalation reactions of hydroquinone with porous vanadium benzenedicarboxylate MIL-47.

Abstract

One of the enticing features of metal-organic frameworks (MOFs) is the potential to control the chemical and physical nature of the pores through postsynthetic modification. The incorporation of redox active guest molecules inside the pores of the framework represents one strategy toward improving the charge transport properties of MOFs. Herein, we report the vapor-phase redox intercalation of an electroactive organic compound, hydroquinone (H2Q) or benzene-1,4-diol, into the channels of the host [V(IV)O(bdc)], (bdc =1,4-benzenedicarboxylate) conventionally denoted as MIL-47. The temperatures and especially the atmosphere in which the reactions took place were found to determine the products. In ambient atmosphere, quinhydrone charge-transfer complexes are formed inside the channels. Under anhydrous conditions, the framework itself was functionalized by a radical anion species derived from the pyrolysis of hydroquinone. Both cases are accompanied by the reduction of V(4+) to V(3+) via single-crystal-to-single-crystal transformations. The products were characterized by single crystal X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, and electron paramagnetic resonance spectroscopy.