Iodine Adsorption in a Redox-Active Metal-Organic Framework: Electrical Conductivity Induced by Host-Guest Charge-Transfer

We report a comparative study of the binding of I-2 (iodine) in a pair of redox-active metal-organic framework (MOF) materials, MFM-300(V-III) and its oxidized, deprotonated analogue, MFM-300(V-IV). Adsorption of I-2 in MFM-300(V-III) triggers a host-to-guest charge-transfer, accompanied by a partial (similar to 30%) oxidation of the V-III centers in the host framework and formation of I-3(-) species residing in the MOF channels. Importantly, this charge-transfer induces a significant enhancement in the electrical conductivity (Delta(sigma) = 700000) of I-2@MFM-300(V-III/IV) in comparison to MFM-300(V-III). In contrast, no host-guest charge-transfer or apparent change in the conductivity was observed upon adsorption of I-2 in MFM-300(V-IV). High-resolution synchrotron X-ray diffraction of ( )2 pMFM-300(V-III/IV()) confirms the first example of self-aggregation of adsorbed iodine species (I-2 and I-3(-)) into infinite helical chains within a MOF.