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

Isostructural metalorganic frameworks (MOFs) M-2(TTFTB) (M = Mn, Co, Zn, and Cd; H4TTFTB = tetrathiafulvalene tetrabenzoate) exhibit a striking correlation between their single-crystal conductivities and the shortest S center dot center dot center dot 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 neighboring S and C atoms. Density functional theory 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 analogue, with the largest cation and shortest S center dot center dot center dot S contact, shows the largest electrical conductivity, pi = 2.86 (+/- 0.53) X 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 controlling charge transport in MOFs with pi-stacked motifs.