Heterospin frustration in a metal-fullerene-bonded semiconductive antiferromagnet

Yongbing Shen; Mengxing Cui; Shinya Takaishi; Hideyuki Kawasoko; Kunihisa Sugimoto; Takao Tsumuraya; Akihiro Otsuka; Eunsang Kwon; Takefumi Yoshida; Norihisa Hoshino; Kazuhiko Kawachi; Yasuhiko Kasama; Tomoyuki Akutagawa; Tomoteru Fukumura; Masahiro Yamashita

doi:10.1038/s41467-022-28134-w

Heterospin frustration in a metal-fullerene-bonded semiconductive antiferromagnet

Nat Commun. 2022 Jan 25;13(1):495. doi: 10.1038/s41467-022-28134-w.

Authors

Yongbing Shen¹, Mengxing Cui², Shinya Takaishi², Hideyuki Kawasoko², Kunihisa Sugimoto³, Takao Tsumuraya⁴, Akihiro Otsuka^{5

6}, Eunsang Kwon⁷, Takefumi Yoshida², Norihisa Hoshino⁸, Kazuhiko Kawachi⁹, Yasuhiko Kasama⁹, Tomoyuki Akutagawa⁸, Tomoteru Fukumura^{2

10}, Masahiro Yamashita^{11

12}

Affiliations

¹ Department of Chemistry, Graduate School of Science, Tohoku University, 6-3 Aza-Aoba, Aramaki, Sendai, 980-8578, Japan. shen.yongbing.b1@tohoku.ac.jp.
² Department of Chemistry, Graduate School of Science, Tohoku University, 6-3 Aza-Aoba, Aramaki, Sendai, 980-8578, Japan.
³ Diffraction & Scattering Division Synchrotron Radiation Research Institute, Hyogo, 679-5198, Japan.
⁴ Priority Organization for Innovation and Excellence, Kumamoto University, 2-39-1 Kurokami, Kumamoto, 860-8555, Japan.
⁵ Division of Chemistry, Graduate School of Science, Kyoto University, Sakyo-Ku, Kyoto, 606-8502, Japan.
⁶ Research Center for Low Temperature and Materials Sciences, Kyoto University, Sakyo-Ku, Kyoto, 606-8501, Japan.
⁷ Research and Analytical Center for Giant Molecules, Tohoku University, 6-3, Aramaki-Aza-Aoba, Aoba-ku, Sendai, 980-8578, Japan.
⁸ Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-Ku, Sendai, 980-8577, Japan.
⁹ Idea International Co., Ltd., 1-15-35 Sagigamori, Aoba-ku, Sendai, 981-0922, Japan.
¹⁰ Advanced Institute for Materials Research and Core Research Cluster, Tohoku University, Sendai, 980-8577, Japan.
¹¹ Department of Chemistry, Graduate School of Science, Tohoku University, 6-3 Aza-Aoba, Aramaki, Sendai, 980-8578, Japan. yamasita@agnus.chem.tohoku.ac.jp.
¹² School of Materials Science and Engineering, Nankai University, Tianjin, 300350, China. yamasita@agnus.chem.tohoku.ac.jp.

Abstract

Lithium-ion-encapsulated fullerenes (Li⁺@C₆₀) are 3D superatoms with rich oxidative states. Here we show a conductive and magnetically frustrated metal-fullerene-bonded framework {[Cu₄(Li@C₆₀)(L)(py)₄](NTf₂)(hexane)}_n (1) (L = 1,2,4,5-tetrakis(methanesulfonamido)benzene, py = pyridine, NTf₂^- = bis(trifluoromethane)sulfonamide anion) prepared from redox-active dinuclear metal complex Cu₂(L)(py)₄ and lithium-ion-encapsulated fullerene salt (Li⁺@C₆₀)(NTf₂^-). Electron donor Cu₂(L)(py)₂ bonds to acceptor Li⁺@C₆₀ via eight Cu‒C bonds. Cu-C bond formation stems from spontaneous charge transfer (CT) between Cu₂(L)(py)₄ and (Li⁺@C₆₀)(NTf₂^-) by removing the two-terminal py molecules, yielding triplet ground state [Cu₂(L)(py)₂]⁺(Li⁺@C₆₀^•-), evidenced by absorption and electron paramagnetic resonance (EPR) spectra, magnetic properties and quantum chemical calculations. Moreover, Li⁺@C₆₀^•- radicals (S = ½) and Cu²⁺ ions (S = ½) interact antiferromagnetically in triangular spin lattices in the absence of long-range magnetic ordering to 1.8 K. The low-temperature heat capacity indicated that compound 1 is a potential candidate for an S = ½ quantum spin liquid (QSL).