TY - JOUR
T1 - Direct Observation of Modulated Radical Spin States in Metal-Organic Frameworks by Controlled Flexibility
AU - Chen, Xiaofeng
AU - Xie, Haomiao
AU - Lorenzo, Emmaline R.
AU - Zeman, Charles J.
AU - Qi, Yue
AU - Syed, Zoha H.
AU - Stone, Aaron E.B.S.
AU - Wang, Yao
AU - Goswami, Subhadip
AU - Li, Peng
AU - Islamoglu, Timur
AU - Weiss, Emily A.
AU - Hupp, Joseph T.
AU - Schatz, George C.
AU - Wasielewski, Michael R.
AU - Farha, Omar K.
N1 - Funding Information:
This work was supported as part of the Inorganometallic Catalyst Design Center, an EFRC funded by the DOE, Office of Science, Basic Energy Sciences (DE-SC0012702). This work made use of the IMSERC Crystallography facility at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-2025633), and Northwestern University. X.C. is grateful to Prof. Kirk S. Schanze for his support and acknowledges financial aid from the National Natural Science Foundation of China (21803038), Shanghai Municipal Education Commission, and China Scholarship Council (CSC) (202008310054) during her visit at Northwestern University. E.R.L. and Z.H.S. are supported by a National Science Foundation Graduate Research Fellowship (DGE-1842165). We thank Dr. Zhijie Chen for critical reading and comments. We also thank Dr. Matthew Krzyaniak, Dr. Ryan Young, and Dr. Yunfan Qiu for helpful discussions. Theory calculations (C.J.Z. and G.C.S.), EPR spectroscopy (E.R.L., Y.Q., and M.R.W.), and E.A.W. were supported as part of the Center for Molecular Quantum Transduction, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under Award No. DE-SC0021314.
Publisher Copyright:
© 2022 American Chemical Society.
PY - 2022/2/16
Y1 - 2022/2/16
N2 - Owing to their switchable spin states and dynamic electronic character, organic-based radical species have been invoked in phenomena unique to a variety of fields. When incorporated in solid state materials, generation of organic radicals proves challenging due to aggregation. Metal-organic frameworks (MOFs) are promising candidates for immobilization and stabilization of organic radicals because of the tunable spatial arrangement of organic linkers and metal nodes, which sequesters the reactive species. Herein, a flexible, redox-active tetracarboxylic acid linker bearing two imidazole units was chosen to construct a new Zr6-MOF, NU-910, with scu topology. By exploiting the structural flexibility of NU-910, we successfully modulate the dynamics between an isolated organic radical species and an organic radical π-dimer species in the MOF system. Single-crystal X-ray diffraction analysis reveals that through solvent exchange from N,N-diethylformamide to acetone, NU-910 undergoes a structural contraction with interlinker distances decreasing from 8.32 Å to 3.20 Å at 100 K. Organic radical species on the bridging linkers are generated via UV light irradiation. Direct observation of temperature-induced spin switches from an isolated radical species to a magnetically silent radical π-dimer in NU-910 after irradiation in the solid state was achieved via variable-temperature single-crystal X-ray diffraction and variable-temperature electron paramagnetic resonance spectroscopy. Ultraviolet-visible-near infrared spectroscopy and density functional theory calculations further substantiated the formation of a radical cation π-dimer upon irradiation. This work demonstrates the potential of using flexible MOFs as a platform to modulate radical spin states in the solid phase.
AB - Owing to their switchable spin states and dynamic electronic character, organic-based radical species have been invoked in phenomena unique to a variety of fields. When incorporated in solid state materials, generation of organic radicals proves challenging due to aggregation. Metal-organic frameworks (MOFs) are promising candidates for immobilization and stabilization of organic radicals because of the tunable spatial arrangement of organic linkers and metal nodes, which sequesters the reactive species. Herein, a flexible, redox-active tetracarboxylic acid linker bearing two imidazole units was chosen to construct a new Zr6-MOF, NU-910, with scu topology. By exploiting the structural flexibility of NU-910, we successfully modulate the dynamics between an isolated organic radical species and an organic radical π-dimer species in the MOF system. Single-crystal X-ray diffraction analysis reveals that through solvent exchange from N,N-diethylformamide to acetone, NU-910 undergoes a structural contraction with interlinker distances decreasing from 8.32 Å to 3.20 Å at 100 K. Organic radical species on the bridging linkers are generated via UV light irradiation. Direct observation of temperature-induced spin switches from an isolated radical species to a magnetically silent radical π-dimer in NU-910 after irradiation in the solid state was achieved via variable-temperature single-crystal X-ray diffraction and variable-temperature electron paramagnetic resonance spectroscopy. Ultraviolet-visible-near infrared spectroscopy and density functional theory calculations further substantiated the formation of a radical cation π-dimer upon irradiation. This work demonstrates the potential of using flexible MOFs as a platform to modulate radical spin states in the solid phase.
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U2 - 10.1021/jacs.1c11417
DO - 10.1021/jacs.1c11417
M3 - Article
C2 - 35129331
AN - SCOPUS:85124636045
VL - 144
SP - 2685
EP - 2693
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 6
ER -