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
Abstract
Abstract Lithium-ion-encapsulated fullerenes (Li + @C 60 ) are 3D superatoms with rich oxidative states. Here we show a conductive and magnetically frustrated metal–fullerene-bonded framework {[Cu 4 (Li@C 60 )(L)(py) 4 ](NTf 2 )(hexane)} n ( 1 ) ( L = 1,2,4,5-tetrakis(methanesulfonamido)benzene, py = pyridine, NTf 2 − = bis(trifluoromethane)sulfonamide anion) prepared from redox-active dinuclear metal complex Cu 2 (L)(py) 4 and lithium-ion-encapsulated fullerene salt (Li + @C 60 )(NTf 2 − ). Electron donor Cu 2 (L)(py) 2 bonds to acceptor Li + @C 60 via eight Cu‒C bonds. Cu–C bond formation stems from spontaneous charge transfer (CT) between Cu 2 (L)(py) 4 and (Li + @C 60 )(NTf 2 − ) by removing the two-terminal py molecules, yielding triplet ground state [Cu 2 (L)(py) 2 ] + (Li + @C 60 •− ), evidenced by absorption and electron paramagnetic resonance (EPR) spectra, magnetic properties and quantum chemical calculations. Moreover, Li + @C 60 •− radicals ( S = ½) and Cu 2+ 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).