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

Michael L. Aubrey, Brian M. Wiers, Sean C. Andrews, Tsuneaki Sakurai, Sebastian E. Reyes-Lillo, Samia M. Hamed, Chung-Jui Yu, Lucy E. Darago, Jarad A. Mason, Jin-Ook Baeg, Fernande Grandjean, Gary J. Long, Shu Seki, Jeffrey B. Neaton, Peidong Yang, Jeffrey R. Long

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 x Fe2(BDP)3 (0 ≤ x ≤ 2; BDP2- = 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 Fe2(BDP)3 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 x Fe2(BDP)3 field-effect transistor represents the realization of a general synthetic strategy for the creation of new porous conductor-based devices.