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

Abstract

Isostructural metal-organic frameworks (MOFs) 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 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···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 controlling charge transport in MOFs with π-stacked motifs.

Electrically Conductive Porous Metal–Organic Frameworks

“…[72,73] All four of these MOFs are isostructural, with TTF moieties forming p-p stacked 1D helical columns with relatively short S···S interactions between neighboring TTF molecules running parallel to infinite metal carboxylate SBUs ( Figure 6). They exhibit BET surface areas between 470 and 540 m 2 mmol À1 .…”

“…Mn 2 (TTFTB) [73] 8.6 10 À5 (crystal, 2-probe) [ [52] 3.9 10 À6 (pellet, 2-probe) [g,i] N.R. Fe 2 (DOBDC) [52] 3.2 10 À7 Scm À1 (pellet, 2-probe) [g,i] N.R.…”

Recent Progress in Metal‐Organic Frameworks for Applications in Electrocatalytic and Photocatalytic Water Splitting

“…Park et al found that isostructural MOFs M 2 (TTFTB) (M = Mn, Co, Zn and Cd; H 4 TTFTB = tetrathiafulvalene tetrabenzoate) exhibited a striking correlation between their single‐crystal conductivities and the shortest S···S interaction defined by neighboring tetrathiafulvalene (TTF) cores, which inversely correlated with the ionic radius of the metal ions 132. The Cd analogue, with the largest cation and shortest S···S contact, showed the highest electrical conductivity (2.86 × 10 −4 S cm −1 ) that was 72 times higher than that of Zn 2 (TTFTB) (3.95 × 10 −6 S cm −1 ).…”

Magnetic functionalities in MOFs: from the framework to the pore

“…Thus, the introduction of electrical conductivity into a MOF remains an almost unexplored topic since for the most part these materials are insulators. 3 A recent review that covers this topic has recently been published. 4 As far as luminescent MOFs are concerned, this area has also been extensively reviewed recently for their use in chemical sensing and explosive detection, 5 light-harvesting sensitizers, 6 and light emitting applications.…”