Metal-organic frameworks (MOFs) containing redox active linkers have led to hybrid compounds exhibiting high electrical conductivity, which enables their use in applications in electronics and electrocatalysis. While many computational studies predict two-dimensional (2D) MOFs to be metallic, the majority of experiments show decreasing conductivity on cooling, indicative of a gap in the electronic band structure. To date, only a handful of MOFs have been reported that exhibit increased electrical conductivity upon cooling indicative of a metallic character, which highlights the need for a better understanding of the origin of the conductivity. A 2D MOF containing iron bis(dithiolene) motifs was recently reported to exhibit semiconducting behavior with record carrier mobility. Herein, we report that high crystallinity and the elimination of guest species results in an iron 2,3,6,7,10,11-tripheylenehexathiolate (THT) MOF, FeTHT, exhibiting a complex transition from semiconducting to metallic upon cooling, similar to what was shown for the analogous CoTHT. Remarkably, exposing the FeTHT to air significantly influences the semiconducting-to-metallic transition temperature (100 to 300 K) and ultimately results in a material showing metallic-like character at, and above, room temperature. This study indicates these materials can tolerate a substantial degree of doping that ultimately results in charge delocalization and metallic-like conductivity, an important step toward enabling their use in chemiresistive sensing and optoelectronics.
Bibliographical noteFunding Information:
We are grateful to the University of Southern California (USC) and the USC Women in Science and Engineering for funding. A.J.C. gratefully acknowledges support from the Norma and Jerol Sonosky Fellowship and the USC Wrigley Institute. A.J.N and B.C.M. gratefully acknowledge funding through Office of Naval Research Grant No. N00014-15-1-2411. S.A.H. was supported as part of the Multidisciplinary GAANN in Smart Energy Materials, a Graduate Areas of National Need, funded by the U.S. Department of Education, under Award P200A150135. J.M.S. is grateful to the UK Engineering and Physical Sciences Council (Grant No. EP/P007821/1) and to the University of Manchester for the support of a Presidential Fellowship. SEM data were collected at the Center for Electron Microscopy and Microanalysis (CEMMA), USC. Use of the Advanced Photon Source at Argonne National Laboratory was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. We are grateful to Prof. Mark Thompson for allowing the use of the Agilent 5420 SPM instrument for AFM studies. We thank Sara Smock for assistance with the BET measurements. The computational modelling studies were carried out using the UK Archer HPC facility through the UK Materials Chemistry Consortium, which is funded by the EPSRC (Grant. No. EP/L000202).
Copyright © 2019 American Chemical Society.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry