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Metallic and Mott Insulating Spin‐Frustrated Antiferromagnetic States in Ionic Fullerene Complexes with a Two‐Dimensional Hexagonal C 60 .− Packing Motif
Author(s) -
Konarev Dmitri V.,
Khasanov Salavat S.,
Otsuka Akihiro,
Maesato Mitsuhiko,
Uruichi Mikio,
Yakushi Kyuya,
Shevchun Artem F.,
Yamochi Hideki,
Saito Gunzi,
Lyubovskaya Rimma N.
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201304763
Subject(s) - antiferromagnetism , fullerene , condensed matter physics , materials science , metal , crystallography , optical conductivity , spins , frustration , chemistry , physics , organic chemistry , metallurgy
(MDABCO + )(C 60 .− )(TPC) ( 1 ), in which MDABCO + is N ‐methyldiazabicyclooctanium, TPC is triptycene, and both have threefold symmetry, is a rare example of a fullerene‐based quasi‐2D metal and contains closely packed hexagonal fullerene layers with interfullerene center‐to‐center distances of 10.07 Å at 300 K. Evidence for the metallic nature of 1 was obtained by optical and microwave conductivity measurements on single crystals. The metal is characterized by a nontypical Drude response and relatively large optical mass ( m */ m 0 =6.7). The latter indicates a narrow‐band nature, which is consistent with the calculated bandwidth of 0.10–0.15 eV. The coexistence of metallic and antiferromagnetic nonmetallic 2D layers was observed in 1 above 200–230 K. It was assumed that the nonmetallic layers undergo a transition to the metallic state below 200 K due to ordering of the fullerene and cationic sublattices. New layered complex (MQ + )(C 60 .− )(TPC) ( 2 ) with a hexagonal arrangement of C 60 .− was obtained by increasing the interfullerene distance with the bulkier N ‐methylquinuclidinium cations (MQ + ) having threefold symmetry. The structure of 2 is characterized by increased interfullerene center‐to‐center distances in the layers (10.124, 10.155, and 10.177 Å at 250 K). Unit‐cell doubling parallel to the 2D layer (along the b axis) was observed at low temperatures. In contrast to metallic 1 , 2 exhibits a nonmetallic spin‐frustrated state with an antiferromagnetic interaction of spins (the Weiss temperature is −27 K) and no magnetic ordering down to 1.9 K. It was supposed that the expanded interfullerene distances in the triangular arrangement decrease the bandwidth and suppress metallic conductivity in 2 , and thus a Mott–Hubbard insulating state with antiferromagnetically frustrated spins results.