Mitsuhiko Maesato

Spin liquid state in an organic Mott insulator with a triangular lattice

1H NMR and static susceptibility measurements have been performed in an organic Mott insulator with a nearly isotropic triangular lattice, kappa-(BEDT-TTF)2Cu2(CN)(3), which is a model system of frustrated quantum spins. The static susceptibility is described by the spin S=1/2 antiferromagnetic triangular-lattice Heisenberg model with the exchange constant J approximately 250 K. Regardless of the large magnetic interactions, the 1H NMR spectra show no indication of long-range magnetic ordering down to 32 mK, which is 4 orders of magnitude smaller than J. These results suggest that a quantum spin liquid state is realized in the close proximity of the superconducting state appearing under pressure.

Proton-Conductive Magnetic Metal–Organic Frameworks, {NR3(CH2COOH)}[MaIIMbIII(ox)3]: Effect of Carboxyl Residue upon Proton Conduction

Proton-conductive magnetic metal-organic frameworks (MOFs), {NR(3)(CH(2)COOH)}[M(a)(II)M(b)(III)(ox)(3)] (abbreviated as R-M(a)M(b): R = ethyl (Et), n-butyl (Bu); M(a)M(b) = MnCr, FeCr, FeFe) have been studied. The following six MOFs were prepared: Et-MnCr·2H(2)O, Et-FeCr·2H(2)O, Et-FeFe·2H(2)O, Bu-MnCr, Bu-FeCr, and Bu-FeFe. The structure of Bu-MnCr was determined by X-ray crystallography. Crystal data: trigonal, R3c (#161), a = 9.3928(13) Å, c = 51.0080(13) Å, Z = 6. The crystal consists of oxalate-bridged bimetallic layers interleaved by {NBu(3)(CH(2)COOH)}(+) ions. Et-MnCr·2H(2)O and Bu-MnCr (R-MnCr MOFs) show a ferromagnetic ordering with T(C) of 5.5-5.9 K, and Et-FeCr·2H(2)O and Bu-FeCr (R-FeCr MOFs) also show a ferromagnetic ordering with T(C) of 11.0-11.5 K. Et-FeFe·2H(2)O and Bu-FeFe (R-FeFe MOFs) belong to the class II of mixed-valence compounds and show the magnetism characteristic of Néel N-type ferrimagnets. The Et-MOFs (Et-MnCr·2H(2)O, Et-FeCr·2H(2)O and Et-FeFe·2H(2)O) show high proton conduction, whereas the Bu-MOFs (Bu-MnCr, Bu-FeCr, and Bu-FeFe) show moderate proton conduction. Together with water adsorption isotherm studies, the significance of the carboxyl residues as proton carriers is revealed. The R-MnCr MOFs and the R-FeCr MOFs are rare examples of coexistent ferromagnetism and proton conduction, and the R-FeFe MOFs are the first examples of coexistent Néel N-type ferrimagnetism and proton conduction.

Uniaxial strain method for soft crystals: Application to the control of the electronic properties of organic conductors

We developed the uniaxial strain method to compress a crystalline sample along any direction without involving Poisson’s effect. The uniaxial strain is realized by inserting a composite of either the sample embedded in epoxy or the sample in frozen oil into a cylinder much harder than the sample composite followed by the application of external forces to a piston put on the sample composite. We verified, by using a strain gauge embedded in the epoxy or the frozen oil, that the strain thus created has the uniaxial nature. Resistance measurements on two kinds of organic conductors, α-(BEDT–TTF)2KHg(SCN)4 and α-(BEDT–TTF)2I3 under the uniaxial strain showed novel electric properties that have never been found under hydrostatic pressures. Their properties were found to be largely dominated by the direction of the uniaxial strain even when it is applied along directions in the conducting plane having a two-dimensional nature.

Fabrication of Two‐Dimensional Polymer Arrays: Template Synthesis of Polypyrrole between Redox‐Active Coordination Nanoslits

1 / 1 Institute for Integrated Cell-Material Sciences (iCeMS), Kyoto University Title: Fabrication of Two-Dimensional Polymer Arrays: Template Synthesis of Polypyrrole between Redox-Active Coordination Nanoslits Author: N. Yanai, T. Uemura, M. Ohba, Y. Kadowaki, M. Maesato, M. Takenaka, S. Nishitsuji, H. Hasegawa, and S. Kitagawa Journal: Angew. Chem. Int. Ed., Vol. 47, No. 51, 9883-9886 (2008) Abstract: Oxidative and intercalative polymerization of pyrrole was conducted within the nanoslits of a layered coordination open framework containing redox-active sites. Isolation of polypyrrole from the host framework led to stacked sheet polymer objects whose orientation and morphology are directly related to the original coordination polymer template.

A Two-Dimensional Organic Metal Based on Fullerene†

We report the synthesis and studies of the physical properties of the first two-dimensional (2D) fullerene organic metal to have 2D layers with a honeycomb arrangement of C60C , (MDABCO)·TPC·(C60C ) (1); we employed a multicomponent and molecular symmetry synthetic approach, starting from the N-methyldiazabicyclooctane cation (MDABCO) and triptycene (TPC). Compound 1 is a fascinating example of a material composed of only light elements (C, H, N) that exhibits a metallic state down to 1.9 K. Salts of fullerene C60 with a number of different inorganic cations have previously shown metallic or superconducting properties. Among the fullerene metals, the best known families are MC60 salts (M = K, Rb, Cs), which contain linearly polymerized C60C , and superconducting M3C60 salts (M = alkali metals), obtained by doping C60 with alkali metals, which have transition temperatures (Tc) of up to 38 K. [1–4] As metal cations expand the three-dimensional (3D) lattice of the initial C60 framework, M3C60 salts exhibit 3D metallic conductivity, whereas MC60 salts are either 3D (when M = K) or quasi-1D metals (when M = Rb or Cs). 2D fullerene metals have not yet been obtained, whilst the various possible ways of modifying MxC60 salts have almost been exhausted. The idea of obtaining purely organic molecular metals or superconductors from fullerenes has remained unrealized, despite being considered for many years. None of the C60C salts of organic cations have exhibited metallic properties. The salt (NMe4 )·(C60C )·THF1.5 showed rather high conductivity, yet was a semiconductor. By synthesizing organic molecular crystals from C60 and organic electron donor molecules, it is possible to produce conductors with unique structures and properties. We have developed a multicomponent approach for synthesizing ionic fullerene compounds that enables the synthesis of ionic fullerene solids DI ·DII·C60C of various structures. 7] DI + is a small, strong donor or cation that ionizes C60 and determines its charged state, whereas DII is a large, neutral molecule that defines the crystal packing of the complex. In order to exhibit metallic properties, the fullerene sublattice should have a close-packed structure. However, C60C radical anions have a strong tendency for dimerization, and when they are allowed to approach each other they normally form diamagnetic single-bonded (C60 )2 dimers. [7–9] In this study, by choosing DII molecules with suitable spatial geometry and size, we were able to synthesize a complex with a close-packed fullerene 2D sublattice in which the C60C monomers preferentially form a 2D honeycomb network of C60C rather than undergo dimerization. We expected that TPC (Figure 1), which forms molecular complexes with C60, [10, 11] would offer a suitable geometrical space and spatial regulation as the DII component for C60C ions in ionic multicomponent complexes. Indeed, it forms hexagonal layers with voids that accommodate foreign cations, such as MDABCO (DI ), in the first key–keyhole relationship (Figure 1a). Docking C60C into the periodic hollow sites in the (MDABCO)·TPC network (second key–keyhole relationship; Figure 1a,b) leads to hexagonal packing of the fullerene layers without dimerization of the C60C monomers. We used diffusion to obtain good-quality single crystals of complex 1, which have a rhombohedral structure at 300 K. The C60C radical anions (the charged state was confirmed spectroscopically) formed uniform hexagonal close-packed layers of two types, A and B, which alternate with the (MDABCO)·TPC layers along the c axis (Figure 2a). In type A layers, the C60C radical anions are ordered and packed as shown in Figure 1, with the uncharged nitrogen atoms of the MDABCO cations arranged directly above the fullerene hexagons (Figure 2a,b). Layers of type B show dynamic disorder of the C60C anions at 300 K, with methyl groups of MDABCO cations slightly penetrating into the periodic hollow sites in the hexagonal packing of disordered C60C ions (Figure 2a,c). In both types of layers, each C60C has six fullerene neighbors with an equal center-to-center distance of 10.073(1) at 300 K, which decreases to 9.967(1) at 185 K. In type B layers, the disorder of C60C ions at 300 K could be described as flipping between three symmetrically related orientations of C60C with 1/3 occupancy for each [*] D. V. Konarev, Prof. R. N. Lyubovskaya Institute of Problems of Chemical Physics RAS Chernogolovka, Moscow region, 142432 (Russia) E-mail: konarev@icp.ac.ru

Emergence of inhomogeneous moments from spin liquid in the triangular-lattice Mott insulator κ − ( ET ) 2 Cu 2 ( CN ) 3

The static and dynamic local spin susceptibility of the organic Mott insulator

New organic conductors based on dibromo- and diiodo-TSeFs with magnetic and non-magnetic MX4 counter anions (M = Fe, Ga; X = Cl, Br)

\ensuremath{\kappa}\text{\ensuremath{-}}(\mathrm{ET}{)}_{2}{\mathrm{Cu}}_{2}(\mathrm{CN}{)}_{3}

Single component betainic conductor: pyrimido-fused TTF derivatives having ethylenedioxy group ☆

, a model material of the spin-1/2 triangular lattice, is studied by

Metal-insulator transition of the 1-D half-filled band metal (TTM-TTP)I3

^{13}\mathrm{C}

Pressure-Tuned Exchange Coupling of a Quantum Spin Liquid in the Molecular Triangular Lattice κ-(ET)_{2}Ag_{2}(CN)_{3}.

NMR spectroscopy from room temperature down to