Cation-Dependent Intrinsic Electrical Conductivity in Isostructural Tetrathiafulvalene-Based Microporous Metal-Organic Frameworks

The isostructural metal-organic frameworks M2(TTFTB) (M = Mn, Co, Zn, and Cd; H4TTFTB = tetrathiafulvalene-tetrabenzoate) exhibit a striking correlation between their single crystal conductivities and the shortest S…S interaction defined by neighboring TTF cores, which inversely correlates with the ionic radius of the metal ions. The larger cations cause a pinching of the S…S contact, which is responsible for better orbital overlap between pz orbitals on neigh-boring S and C atoms. DFT calculations show that these orbitals are critically involved in the valence band of these materials, such that modulation of the S…S distance has an important effect on band dispersion and, implicitly, on the conductivity. The Cd analog, with the largest cation and shortest S…S contact shows the largest electrical conductivity, σ = 2.86 (±0.53) × 10-4 S/cm, which is also among the highest in microporous MOFs. These results describe the first demonstration of tunable intrinsic electrical conductivity in this class of materials and serve as a blueprint for con-trolling charge transport in MOFs with π-stacked motifs.