Electron delocalization and charge mobility as a function of reduction in a metal–organic framework

Abstract

Conductive metal-organic frameworks are an emerging class of three-dimensional architectures with degrees of modularity, synthetic flexibility and structural predictability that are unprecedented in other porous materials. However, engendering long-range charge delocalization and establishing synthetic strategies that are broadly applicable to the diverse range of structures encountered for this class of materials remain challenging. Here, we report the synthesis of K Fe(BDP) (0 ≤ x ≤ 2; BDP = 1,4-benzenedipyrazolate), which exhibits full charge delocalization within the parent framework and charge mobilities comparable to technologically relevant polymers and ceramics. Through a battery of spectroscopic methods, computational techniques and single-microcrystal field-effect transistor measurements, we demonstrate that fractional reduction of Fe(BDP) results in a metal-organic framework that displays a nearly 10,000-fold enhancement in conductivity along a single crystallographic axis. The attainment of such properties in a K Fe(BDP) field-effect transistor represents the realization of a general synthetic strategy for the creation of new porous conductor-based devices.

A Phthalocyanine‐Based Layered Two‐Dimensional Conjugated Metal–Organic Framework as a Highly Efficient Electrocatalyst for the Oxygen Reduction Reaction

“…[1,2] Due to the diversity in composition/ structure,h igh surface area, and chemical/thermal stability, MOFs have been applied in many areas including gas separation/storage,s ensors,a nd catalysis. [3][4][5][6][7][8] Recently, MOFs have been rising as af ascinating family of electrocatalysts providing insight in both homogeneous and heterogeneous chemistry:t he well-defined structures and readily accessible active sites can be tuned at the molecular level to improve the catalytic performance and they also enable the MOFs to serve as model systems for the fundamental understanding of catalytic mechanisms.R ecently,v arious MOFs,s uch as [Cu 2 (OH)(bpy) 2 (btc) 3 ], [Fe 2 (Fe(tcpp))Cl], [Cu 3 (btc) 2 (H 2 O) 3 ], and [Co(mim) 2 ], have been explored as oxygen reduction reaction (ORR) electrocatalysts. [2,[9][10][11][12] However,g reat challenges still remain for conventional MOFs including electrical insulators and the blockage of metal centers by organic ligands;this leads to inferior activity (halfwave potential E 1/2 < 0.8 Vv s. RHE) and dramatically limits their broader applications in electrocatalysis.P yrolysis of MOFs to provide metal-and heteroatom-doped porous carbons has been widely demonstrated to improve the catalytic activity.…”

Coupled Electrical Conduction in Coordination Polymers: From Electrons/Ions to Mixed Charge Carriers

“…For example, K x Fe 2 (BDP) 3 is composed of mixed-valence metal node and BDP 2À (BDP 2À = 1,4-benzenedipyrazolate) Linkers. [56] A reduction process forces the obtained crystal to capture some K + ions into the frameworks. After incorporation of the K + ions, this compound showed remarkable enhancement in electronic conductivity by a four-order magnitude.…”

Strategies for Improving the Performance and Application of MOFs Photocatalysts

“…This strategy of using metal ion doping to change the internal energy level of the semiconductor to improve its photocatalytic performance is also useful in super capacitor. Aubrey et al [158] found that through the introduction of K + , the energy band delocalization of semiconductors could be realized, and the conductivity and mobility of MOFs were greatly improved, to a status comparable to these of organic polymers. The researchers believed that this excellent performance is mainly due to the introduction of K + and the resultant production of intervalence charge-transfer (IVÀ CT), which greatly enhanced charge delocalization.…”

“…The double-headed arrow indicates the (001) direction aligned with the long axis of the crystal. Reproduced with permission from Ref [158]…”