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Interpenetration as a Mechanism for Negative Thermal Expansion in the Metal–Organic Framework Cu3(btb)2 (MOF-14)

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  • This work was supported by research and fellowship funding from the Australian Research Council (C.J.K.), and Post-Graduate Research Awards (Y.W.) from the Australian Government and the Australian Institute of Nuclear Science and Engineering (AINSE). Work was undertaken at the Australian Synchrotron MX-1 (M2200) and PD beamlines (M2919) and at the Advanced Photon Source 1-BM-C beamline (GUP-12462). Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. We thank Gregory J. Halder for beamline support.

Abstract

Metal–organic framework materials (MOFs) have recently been shown in some cases to exhibit strong negative thermal expansion (NTE) behavior, while framework interpenetration has been found to reduce NTE in many materials. Using powder and single-crystal diffraction methods we investigate the thermal expansion behavior of interpenetrated Cu3(btb)2 (MOF-14) and find that it exhibits an anomalously large NTE effect. Temperature-dependent structural analysis shows that, contrary to other interpenetrated materials, in MOF-14 the large positive thermal expansion of weak interactions that hold the interpenetrating networks together results in a low-energy contractive distortion of the overall framework structure, demonstrating a new mechanism for NTE.

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