Ni@onion-like carbon and Co@amorphous carbon: control of carbon structures by metal ion species in MOFs

We first report the facile synthesis of metal-carbon composites consisting of metal nanoparticles (NPs) and different types of carbon species: onion-like and amorphous carbon, Ni@onion-like carbon and Co@amorphous carbon. By simply changing the metal species in an isostructural metal-organic framework, thermal decompositions of MOF-74 directly afforded different types of metal NPs and carbon composites, which exhibited good electrical conductivity. In particular, the Ni@onion-like carbon, having a well-ordered carbon structure, had high electrical conductivity (sigma = 5.3 omega(-1) cm(-1) at 295 K), explained by a modified model of the Efros-Shklovskii variable range hopping

Anomalous magnetoresistance and hidden spin canting in (DIETSe)_{2}MCl_{4} (M=Fe, Ga)

The quasi-one-dimensional (Q1D) molecular conductors (DIETSe)_{2}MCl_{4} [M=Fe, Ga] undergo a spin density wave (SDW) transition below 12 K. The SDW ground state is suppressed by applying high pressure, recovering the Q1D Fermi surface which is confirmed by the appearance of Lebed resonance in the angle-dependent magnetoresistance (MR). Above the critical pressure of SDW, MR shows kink structures at high magnetic fields, reminiscent of field-induced spin density wave (FISDW) transition in both salts. The π-d hybrid (DIETSe)_{2}MCl_{4} also exhibits an antiferromagnetic (AF) transition of d-electron spins at 2.5 K, below which the spin-flop-induced positive large MR are observed. The change in the interlayer MR reaches 130% at 10.5 kbar. The resistance anomalies associated with spin flop are also observed in the angle-dependent MR at low magnetic fields below 5 T, associated with clear hysteresis. A polar plot of these anomalies reveals the presence of hidden spin canting. Two magnetic easy axes of d-electron spins are found to be tilted ±16 degrees from the b axis towards the c axis. The interplay between the SDW instability of Q1D π electrons and the local moments of AF d-electron spins is considered as the origin of the anomalous transport behaviors

High‐Performance All‐Solid‐State Proton Rectifier Using a Heterogeneous Membrane Composed of Coordination Polymer and Layered Double Hydroxide

Rational control of unidirectional proton transport is highly challenging, primarily owing to the difficulty in introducing an asymmetric factor into proton conducting media. In this study, freestanding membranes of a proton-conducting two-dimensional porous coordination polymer, Cu₂ (CuTCPP) (H₂ TCPP: 5, 10, 15, 20-tetrakis(4-carboxyphenyl)porphyrin) and a hydroxide ion-conducting layered double hydroxide, Mg-Al-LDH(NO₃ ), were combined to generate a pH gradient in the conducting media. The current–voltage measurements revealed that the heterogeneous membrane exhibits a significant unidirectional proton transport with a proton rectification ratio exceeding 200 under 90% relative humidity in the initial voltage scan. This value is the highest among the reported all-solid-state proton rectifiers. The high designability of both components with well-defined structures, which is in contrast to the organic polymers used so far, provides a new avenue for developing and understanding the protonrectifying behavior in the solid state

Rational Construction of Molecular Electron-Conducting Nanowires Encapsulated in a Proton-Conducting Matrix in a Charge Transfer Salt

Insulated molecular wires have gained significant attention owing to their potential contribution in the fields of nanoelectronics and low-dimensional chemistry/physics. Based on molecular charge transfer salts, we demonstrate, for the first time, the rational construction of molecular electron-conducting wires encapsulated in a proton-conducting matrix, which possibly paves the way to ionoelectronics. As expected from the molecular structure of the newly designed complex anion (i.e., propeller-shaped structure with hydrogen-bonding sites at four edges), a three-dimensional hydrogen-bonded framework was constructed within the crystal, which contains a one-dimensional array of an electron donor, tetrathiafulvalene (TTF). From the single-crystal crystallographic and spectroscopic studies, it was clarified that the nonstoichiometric deprotonation of anions and partial oxidation of TTFs occur, whereas the anion is electronically inert. Moderate conductivities of electron and proton were confirmed by dc and ac conductivity measurements. In addition, the electronic isolation of TTF wires was confirmed by the magnetic susceptibility data

Cationic π-Stacking Columns of Coronene Molecules with Fully Charged and Charge-Disproportionated States

Electrochemical oxidation of a polycyclic aromatic hydrocarbon, coronene, with D6h symmetry in the presence of tetrahedral GaCl4– anions gave two cation salts, (coronene)(GaCl4) (1) and (coronene)5(GaCl4)2 (2), with unprecedented charge arrangements. Salt 1 involves π-stacking columns in a zigzag manner, which are composed of the crystallographically equivalent coronene monocations. First-principle calculations revealed that the dimerization of coronene cations gives rise to a band gap opening at the Fermi level, and thus, semiconducting behavior. On the other hand, in salt 2, two crystallographically independent coronene molecules (A and B) form π-stacking columns with an AABB repeating unit, which are flanked by another coronene molecule (C). The crystallographic features, such as interplanar distances and in-plane molecular distortions arising from the Jahn–Teller effect, as well as the first-principle calculations, strongly suggested the emergence of charge disproportionation within the π-stacking columns. As in the case of 1, the calculated band structure exhibits a band gap opening at the Fermi level, which corresponds to the observed semiconducting behavior

三角格子を持つ新しい有機伝導体の合成と物性

Recently, materials with a triangular lattice have attracted much attention due to their interesting physical properties, such as a quantum spin liquid. It has been reported that organic conductors κ-(ET)2Cu2(CN)3 (1) and κ-(ET)2Ag2(CN)3 (2) show quantum spin liquid behavior, where ET is bis(ethylenedithio) tetrathiafulvalene. These two salts are the only ones known as κ-type ET salt organic conductors with a nearly regular triangular lattice. Therefore, in order to develop new materials with a regular triangular lattice, we synthesized κ-(ET)2Cu2xAg2(1-x)(CN)3 (3) by mixing Cu+ and Ag+ ions. We analyzed the element distribution and composition ratio in the crystal by scanning electron microscope (SEM) and energy dispersive x-ray spectroscope (EDX). The Cu+ and Ag+ ions were distributed uniformly in the crystals. The x was found to be x = 0.82 ± 0.01 for batch #1, and x = 0.81 ± 0.06 for batch #2. The mixed crystal showed semiconducting behavior with activation energy (Ea/kB) of 711 K. This material is considered a Mott insulator.近年, 三角格子を持つ物質はスピン液体などの興味深い性質を持つことで注目されている. κ-(ET)2Cu2(CN)3 とκ-(ET)2Ag2(CN)3は三角格子を持つモット絶縁体であり, スピン液体の振る舞いを示すことが報告されている. しかし, ほぼ正三角形の構造を持つκ 型ET塩有機伝導体はこの二つしか知られていない. そこで, 今回我々は新しい正三角形の構造を持つ物質を開発するために, 銅イオンと銀イオンを混ぜて, 有機伝導体の混晶試料κ-(ET)2Cu2xAg2(1-x)(CN)3 を合成した. 2 種類のバッチ（#1, #2）について結晶構造と物性を調べた. X線構造解析によって, この混晶は同形構造を持つことが分かった. SEM/EDX分析により, 結晶内の元素分布や組成比を調べた結果, 銅イオンと銀イオンはともに結晶内に一様に分布し, その比は上記の化学式において, #1 ではx = 0.82±0.01, #2 ではx = 0.81±0.06であることが分かった. また, #2 の結晶について面内の電気抵抗を測定した結果, 半導体的な挙動を示し, その活性化エネルギー（Ea/kB）は711 K であった. これは二つの母物質の活性化エネルギーの値の中間であることから, 得られた混晶はモット絶縁体であると考えられる