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