Novel Electronic States of Partially Deuterated (DMe-DCNQI)2Cu
15 Jul 1993-Journal of the Physical Society of Japan (THE PHYSICAL SOCIETY OF JAPAN)-Vol. 62, Iss: 7, pp 2224-2228
TL;DR: Magnetic and structural studies of giant metal (M)-insulator (I)-metal reentrant transitions in the partially deuterated molecular conductors (DMe-DCNQI- d n ) 2 Cu ( n =2, 3) are presented in this paper.
Abstract: Magnetic and structural studies of giant metal (M)-insulator (I)-metal reentrant transitions in the partially deuterated molecular conductors (DMe-DCNQI- d n ) 2 Cu ( n =2, 3) are presented. In the insulating phase, Curie-Weiss-like susceptibilities with reduced Curie constants and diffusive satellite reflections showing a threefold superstructure were observed. The results are discussed in terms of novel electronic states associated with the 3D narrow ` d -band' in the 1D 2 p π conduction band.
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TL;DR: In this paper, structural and physical properties of the Cu salts of a series of π-acceptors N,N′-dicyanobenzoquinonediimines (DCNQIs) are described.
Abstract: Structural and physical properties of the Cu salts of a series of π-acceptors N,N′-dicyanobenzoquinonediimines (DCNQIs) are described. The most notable feature of this system is that 3d electrons in Cu interact with pπ electrons in DCNQI near the Fermi level. This unique feature has provided a lot of interesting solid state properties: the Mott transition triggered by the Peierls transition, the pressure-induced metal-insulator transition, the metal-insulator-metal (reentrant) transition, the three-dimensional Fermi surface, the anomalous isotope effects, the antiferromagnetic transition, the weak ferromagnetism, and the electron mass enhancement. The aim of this account is to give an overview of this unique pπ-d system.
101 citations
66 citations
TL;DR: Electron spin resonance measurements indicate that the UV irradiation reversibly generates carriers and localized spins on the Ni( dmit)(2) and the BPY, respectively, which can be explained by charge transfer transitions between Ni(dmit)( 2) and BPY in the UV region.
Abstract: UV irradiation reversibly switches a new insulating and nonmagnetic molecular crystal, BPY[Ni(dmit)2]2 (BPY = N,N′-ethylene-2,2′-bipyridinium; Ni(dmit)2 = bis(1,3-dithiole-2-thione-4,5-dithiolato)nickelate(III)), into a magnetic conductor. This is possible because the bipyridyl derivative cations (BPY2+) trigger a photochemical redox reaction in the crystal to produce a change of ∼10% in the filling of the Ni(dmit)2 valence band, leaving localized spins on the BPY themselves. In the dark, almost all of the BPY molecules are closed-shell cations, and most of the Ni(dmit)2 radical anions form spin-singlet pairs; thus, this material is a diamagnetic semiconductor. Under UV irradiation, a photocurrent is observed, which enhances the conductivity by 1 order of magnitude. Electron spin resonance measurements indicate that the UV irradiation reversibly generates carriers and localized spins on the Ni(dmit)2 and the BPY, respectively. This high photoconductivity can be explained by charge transfer (CT) transition...
31 citations
20 Jul 2021
TL;DR: A short review article as discussed by the authors provides the reader with a summary of the history of organic conductors and how they have evolved over the last two decades, focusing on the last 20 years.
Abstract: This short review article provides the reader with a summary of the history of organic conductors. To retain a neutral and objective point of view regarding the history, background, novelty, and details of each research subject within this field, a thousand references have been cited with full titles and arranged in chronological order. Among the research conducted over ~70 years, topics from the last two decades are discussed in more detail than the rest. Unlike other papers in this issue, this review will help readers to understand the origin of each topic within the field of organic conductors and how they have evolved. Due to the advancements achieved over these 70 years, the field is nearing new horizons. As history is often a reflection of the future, this review is expected to show the future directions of this research field.
28 citations
TL;DR: In this paper, the temperature dependence of magnetic susceptibility of Cu salt of DMe-DCNQI-α, α'-d 2 has been investigated over the temperature range of the metal-insulator-metal (M-I-M) reentrant transition.
Abstract: Temperature dependence of magnetic susceptibility of Cu salt of DMe-DCNQI-α, α'- d 2 has been investigated over the temperature range of the metal-insulator-metal (M-I-M) reentrant transition. The insulating phase of this salt has been revealed to exhibit the same temperature dependence of susceptibility as that of the insulator phase of (DMe-DCNQI- d 8 ) 2 Cu, which shows only a M-I transition. In the reentrant metallic phase, there is no sizable enhancement of susceptibility such as expected from the specific heat enhancement.
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TL;DR: In this article, the X-ray satellite reflections that indicate the periodic lattice distortion with a period of 3c appear below the metal-insulator transition temperature (T{sub M-1}).
Abstract: Crystal structures of a series of highly conductive anion-radical salts with formula (2,5-R{sub 1},R{sub 2}-DCNQI){sub 2}Cu (DCNQI = N,N{prime}-dicyanoquinonediimine; R{sub 1}, R{sub 2} = CH{sub 3}, CH{sub 3}O, Cl, Br) have been studied at room temperature and 100 K. at room temperature, all these compounds are isostructural (tetragonal, space group I4{sub 1}/a). The structure consists of a face-to-face DCNQI column along the crystallographic c axis. The Cu cation is coordinated in D{sub 2d} distorted tetrahedral fashion to the N atoms of the DCNQI molecules. The metal-insulator transition in this system is attended by an abrupt concentration of the c axis. The X-ray satellite reflections that indicate the periodic lattice distortion with a period of 3c appear below the metal-insulator transition temperature (T{sub M-1}).
255 citations
TL;DR: In this article, the structural and electrical properties of new radical anion salts of dicyanoquinodiimine derivatives have been investigated (R1,R2-DCNQI)2M (R 1,R 2-CH3,Cl, MCu).
193 citations
TL;DR: A new family of organic molecules, 2-${R}_{1}$-5-${ R}_{2}$ -DCNQI (with ${R}{1}$,${R}µ$=${\mathrm{CH}}_{3}$, ${\Mathrm{NH}}_{4}$), were investigated by the measurements of electrical conductivity, thermoelectric power, and electron spin resonance, which are appropriately understood by classifying them into three groups as discussed by the authors.
Abstract: A new family of organic molecules, 2-${R}_{1}$-5-${R}_{2}$-DCNQI (with ${R}_{1}$,${R}_{2}$=${\mathrm{CH}}_{3}$, ${\mathrm{CH}}_{3}$O, Cl, or Br; DCNQI=N,N'-dicyanoquinonediimine) works as a ligand as well as an electron acceptor to form highly conducting, charge-transfer and coordination compounds as (2-${R}_{1}$-5-${R}_{2}$-DCNQI${)}_{2}$M (with M=Cu, Ag, Li, Na, K, or ${\mathrm{NH}}_{4}$) These salts are investigated by the measurements of electrical conductivity, thermoelectric power, and electron spin resonance, which are appropriately understood by classifying them into three groups Group-I DCNQI salts consisting of the salts with cations M other than Cu, undergo the Peierls transitions between 50 and 100 K Their thermoelectric power is interpreted by the large-U limit of the Hubbard model Group-II DCNQI salts, the Cu salts of the halogen-substituted DCNQI, also exhibit the Peierls transitions between 150 and 250 K, followed by the antiferromagnetic transitions around 10 K With the one-dimensional tight-binding approximation, the bandwidth is estimated to be 04--05 eV Group-III DCNQI salts, the Cu salts with ${R}_{1}$=${R}_{2}$=${\mathrm{CH}}_{3}$ or ${\mathrm{CH}}_{3}$O retain metallic conductivity down to 15 K, whereas a magnetic transition takes place at 55 K This may be the first organic conductor in which metallic conduction and a magnetic order coexist The magnetic order is attributed to the comparatively localized ${\mathrm{Cu}}^{2+}$ spins present independently of the conduction electrons on DCNQI, where the average oxidation state of Cu has been estimated to be ${\mathrm{Cu}}^{13+}$ AE
105 citations
TL;DR: The mixed valency of Cu in the DCNQI-Cu system suggests a large enhancement of the electron mass at the critical situation where the system begins to exhibit a characteristic metal instability.
Abstract: The unique molecular conductors with p\ensuremath{\pi}-d mixing band structures (${\mathit{R}}_{1}$,${\mathit{R}}_{2\mathrm{\ensuremath{-}}}$N,N'-dicyanoquinonediimine${)}_{2}$Cu [(${\mathit{R}}_{1}$,${\mathit{R}}_{2\mathrm{\ensuremath{-}}}$DCNQI${)}_{2}$Cu] (${\mathit{R}}_{1}$,${\mathit{R}}_{2}$=${\mathrm{CH}}_{3}$,${\mathrm{CH}}_{3}$O,Cl,Br) were examined. General features of the phase diagram of the DCNQI-Cu system were depicted. A region that is related to the existence of anomalously heavy-metal electrons has been found. The ${\mathit{T}}^{2}$ dependence of the low-temperature resistivity of the alloyed system (${\mathrm{DMe}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{MeBr}}_{\mathit{x}\mathrm{\ensuremath{-}}}$DCNQI${)}_{2}$Cu (where Me=${\mathrm{CH}}_{3}$) suggests a large enhancement of the electron mass at the critical situation where the system begins to exhibit a characteristic metal instability. The mixed valency of Cu (${\mathrm{Cu}}^{+1.3}$) in (DMe-DCNQI${)}_{2}$Cu was confirmed by ir experiments performed on neutral DMe-DCNQI crystals and (DMe-DCNQI${)}_{2}$M (M=Li, Ba, Cu).
88 citations