Two Distinct Redox Intercalation Reactions of Hydroquinone with Porous Vanadium Benzenedicarboxylate MIL-47

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 [VIVO­(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 V4+ to V3+ 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.