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Issue 26, 2020
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Two-dimensional, conductive niobium and molybdenum metal–organic frameworks

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Abstract

The incorporation of second-row transition metals into metal–organic frameworks could greatly improve the performance of these materials across a wide variety of applications due to the enhanced covalency, redox activity, and spin–orbit coupling of late-row metals relative to their first-row analogues. Thus far, however, the synthesis of such materials has been limited to a small number of metals and structural motifs. Here, we report the syntheses of the two-dimensional metal–organic framework materials (H2NMe2)2Nb2(Cl2dhbq)3 and Mo2(Cl2dhbq)3 (H2Cl2dhbq = 3,6-dichloro-2,5-dihydroxybenzoquinone), which feature mononuclear niobium or molybdenum metal nodes and are formed through reactions driven by metal-to-ligand electron transfer. Characterization of these materials via X-ray absorption spectroscopy suggests a local trigonal prismatic coordination geometry for both niobium and molybdenum, consistent with their increased covalency relative to related first-row transition metal compounds. A combination of vibrational spectroscopy, magnetic susceptibility, and electronic conductivity measurements reveal that these two frameworks possess distinct electronic structures. In particular, while the niobium compound displays evidence for redox-trapping and strong magnetic interactions, the molybdenum phase is valence-delocalized with evidence of large polaron formation. Weak interlayer interactions in the neutral molybdenum phase enable solvent-assisted exfoliation to yield few-layer hexagonal nanosheets. Together, these results represent the first syntheses of metal–organic frameworks containing mononuclear niobium and molybdenum nodes, establishing a route to frameworks incorporating a more diverse range of second- and third-row transition metals with increased covalency and the potential for improved charge transport and stronger magnetic coupling.

Graphical abstract: Two-dimensional, conductive niobium and molybdenum metal–organic frameworks

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Supplementary files

Article information


Submitted
04 May 2020
Accepted
01 Jun 2020
First published
02 Jun 2020

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2020,11, 6690-6700
Article type
Edge Article

Two-dimensional, conductive niobium and molybdenum metal–organic frameworks

M. E. Ziebel, J. C. Ondry and J. R. Long, Chem. Sci., 2020, 11, 6690 DOI: 10.1039/D0SC02515A

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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