Tunable Mixed-Valence Doping toward Record Electrical Conductivity in a Three-Dimensional Metal–Organic Framework

Abstract

Partial oxidation of an iron-tetrazolate metal-organic framework (MOF) upon exposure to ambient atmosphere yields a mixed-valence material with single-crystal conductivities tunable over 5 orders of magnitude and exceeding 1 S/cm, the highest for a three-dimensionally connected MOF. Variable-temperature conductivity measurements reveal a small activation energy of 160 meV. Electronic spectroscopy indicates the population of midgap states upon air exposure and corroborates intervalence charge transfer between Fe and Fe centers. These findings are consistent with low-lying Fe defect states predicted by electronic band structure calculations and demonstrate that inducing metal-based mixed valency is a powerful strategy toward realizing high and systematically tunable electrical conductivity in MOFs.

Reversible Thermochromism and Strong Ferromagnetism in Two‐Dimensional Hybrid Perovskites

“…Thet emperature-dependent conductivity change suggests athermally activated charge transport mechanism. Fitting the conducting data to the Arrhenius equation s = s 0 exp(ÀE a /k B T) [42,43] can give the activation energy (E a )o ft he materials for charge transport, where s is the electrical conductivity, s 0 is aprefactor, k B is the Boltzmann constant, and T is the absolute temperature.W eobtained an E a of 299 meV for the (PED)CuCl 4 ( Figure S14). In comparison, the E a of (BED) 2 CuCl 6 is estimated to be 960 meV.In2D perovskites,t he organic cations are considered as insulating groups between the conductive inorganic layers.…”

Coordination-induced reversible electrical conductivity variation in the MOF-74 analogue Fe2(DSBDC)

“…Chemically, the dopant molecules may engage with the MOF either through outer-sphere electron transfer (i.e. redox reactivity) [22][23][24][25] or through inner-sphere reactivity. The latter involves binding of guest molecules to coordinatively unsaturated metal centers to form charge transport pathways and/or to inject charge carriers.…”

Redox Tuning in Crystalline and Electronic Structure of Bimetal–Organic Frameworks Derived Cobalt/Nickel Boride/Sulfide for Boosted Faradaic Capacitance

“…However, the CV curves are not amplified proportionally, which is attributed to the absorption peaks with slow scan rates from the porous sheet stacked structure (Figure b). The Co‐Ni‐B‐S presents the highest capacitance with two pairs of redox peaks at the scan rate of 20 mV s −1 , whereas only one pair for the other materials (Co‐Ni MOF, Co‐Ni‐B, Co‐Ni‐S, and Co‐Ni‐S‐B) is resulted from the Co/Ni multivalences and amorphous structure after the redox treatment . The electrochemically active surface area (ECSA) of Co‐Ni MOF and its derivatives are also evaluated through the CV measurements at the potential window (0–0.1 V versus Hg/HgO) (Figure S10, Supporting Information) .…”