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

[Image: see text] 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 (∼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 (Δ(σ) = 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 I(2)@MFM-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.