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. 2020 Sep 1;11(41):11154-11161.
doi: 10.1039/d0sc04040a.

Simultaneous manifestation of metallic conductivity and single-molecule magnetism in a layered molecule-based compound

Yongbing Shen  1 , Hiroshi Ito  2 , Haitao Zhang  3 , Hideki Yamochi  4   5 , Seiu Katagiri  2 , Shinji K Yoshina  2 , Akihiro Otsuka  4   5 , Manabu Ishikawa  4 , Goulven Cosquer  6 , Kaiji Uchida  1 , Carmen Herrmann  3 , Takefumi Yoshida  1 , Brian K Breedlove  1 , Masahiro Yamashita  1   7
Affiliations

Simultaneous manifestation of metallic conductivity and single-molecule magnetism in a layered molecule-based compound

Yongbing Shen et al. Chem Sci. .

Abstract

Single-molecule magnets (SMMs) show superparamagnetic behaviour below blocking temperature at the molecular scale, so they exhibit large magnetic density compared to the conventional magnets. Combining SMMs and molecular conductors in one compound will bring about new physical phenomena, however, the synergetic effects between them still remain unexplored. Here we present a layered molecule-based compound, β''-(BEDO-TTF)4 [Co(pdms)2]·3H2O (BO4), (BEDO-TTF (BO) and H2pdms are bis(ethylenedioxy)tetrathiafulvalene and 1,2-bis(methanesulfonamido)benzene, respectively), which was synthesized by using an electrochemical approach and studied by using crystal X-ray diffraction. This compound simultaneously exhibited metallic conductivity and SMM behaviour up to 11 K for the first time. The highest electrical conductivity was 400-650 S cm-1 at 6.5 K, which is the highest among those reported so far for conducting SMM materials. Furthermore, antiferromagnetic ordering occurred below 6.5 K, along with a decrease in conductivity, and the angle-independent negative magnetoresistance suggested an effective electron correlation between the conducting BO and Co(pdms)2 SMM layers (d-π interactions). The strong magnetic anisotropy and two-dimensional conducting plane play key roles in the low-temperature antiferromagnetic semiconducting state. BO4 is the first compound exhibiting antiferromagnetic ordering among SMMs mediated by π-electrons, demonstrating the synergetic effects between SMMs and molecular conductors.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. Organic conductors and single-molecule magnets. (a) Structural diagrams of BEDT-TTF (ET) and BEDO-TTF (BO). (b) Tetrahedrally coordinated structure of [Co(pdms)2]2−. (c) The evolution of the highest σ by year for the reported conducting SMM materials: black and red dots represent semiconductors and metals, respectively. The original literature abbreviated in this panel is listed in ref. 12.
Fig. 2
Fig. 2. Crystal structure of BO4 at 120 K. (a) A unit cell projected along the b-axis (black: C, blue: Co, pale blue: N, red: O and yellow: S). (b) Packing structure in the bc plane. The SMM layer (green background) alternates with the conducting layer (violet background) via short contacts, and the thicknesses of the SMM and conducting layers are 7.2 Å and 11.0 Å, respectively. (c) The arrangement of the Co ions in the SMM layer in the ab plane. The arrows represent the direction of the easy axis of the Co ions in the Co(pdms)2 molecules. The angle (φ) between three Co ions in one parallelogram is 42°, and the distances between two adjacent Co ions are 8.6 Å and 13.7 Å. (d) The BO molecules arranged side-by-side along the a-axis and face-to-face in the a–b direction. The black dotted lines represent the short contacts (S⋯S and S⋯O) between BO molecules along the a-axis and a–b direction. All hydrogen atoms are omitted for clarity.
Fig. 3
Fig. 3. Magnetic properties. (a) Temperature dependence χT (black circles) in a 0.1 T field in field cooling (FC) and zero field cooling (ZFC) modes, respectively. The solid red lines represent the best fit using anisotropic spins. (b) Magnetic hysteresis of the magnetization at a sweep rate of 200 Oe·s−1 at 2.5 K and the first differential curve of dM/dH (dashed curves) in the range of −0.8 to +0.8 T. (c) A comparison of frequency dependences of out-of-phase ac magnetic susceptibilities χ′′ of BO4 and (HNEt3)2[Co(pdms)2] in a field of 0 Oe. (d) τ as a function of T in fields of 0 and 1500 Oe for BO4 and (HNEt3)2[Co(pdms)2]. The black circles, pink circles and the red curve represent the experimental data and best fit, respectively.
Fig. 4
Fig. 4. Electrical conductivity and magnetoresistance effects. (a) Temperature dependence of σ of two single-crystals using a standard four-probe technique. (b) Magnetic field dependence of MR at different temperatures with the magnetic field perpendicular to the 2D plane, θ = 0°, B‖c-axis. (c) MR–B plot in the range of 0–1.5 T at 2 K, 5 K and 7.5 K at θ = 0°. (d) Magnetic field dependence of MR at different temperatures with the magnetic field parallel to the 2D plane, θ = 90°, B‖b-axis. (e) MR–B plot in the range of 0–1.5 T at 2, 5 and 7.5 K with θ = 90°. (f) The MR–B plot in the range of 0–1.5 T at 2 K with θ = 0° and 90°.
Fig. 5
Fig. 5. DFT calculations. Electronic band structure based on the crystal structure determined by using DFT calculations. High symmetry points in the crystal reciprocal lattice: Γ = (0, 0, 0), X = (0.5, 0, 0), Y = (0, 0.5, 0), Z = (0, 0, 0.5), R = (0.5, −0.5, 0.5), T = (0, 0.5, −0.5), U = (0.5, 0, −0.5), and V = (0.5, −0.5, 0). The Fermi energy level (green dashed line) is set at 2.32 eV. The magenta and black areas and curves indicate Co and BO electrons, respectively.
Fig. 6
Fig. 6. DFT calculations. Fermi surface of BO4 in an extended Brillouin zone, which is composed of electron (blue) and hole (red) pockets associated with the (Γ, X and Y) symmetry points in the bands. Black lines represent the first Brillouin zone, and green dotted lines represent the hidden 1D Fermi surface.
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