Ethylenedithio Tetrathiafulvalene Research Articles

Effective Method for Multi-Probe Electrical Measurements of Organic Single Crystals: Four-Terminal Natural Adhesion Contact

A technique to establish electrical contact and perform multi-probe electrical measurements (e.g., four-probe measurements), even at low temperatures, is presented in this work. The natural adhesion contact (NAC) is applicable to the wide range of dimensions of organic crystals. Furthermore, the precise electrode patterns required to carry out multi-probe measurements are guaranteed, in contrast to fine conductive paste painting methods. We demonstrate four-probe electrical measurements of α-(BEDT-TTF)2I3 (where BEDT-TTF = bis(ethylenedithio) tetrathiafulvalene) at temperatures down to 100 K. The obtained temperature dependence showed a steep meta l–insulator transition and exhibited zero hysteresis throughout several measurement sequences.

Anion Arrangement Effects on Electronic States of κ-type BEDT-TTF Compounds

We investigate the anion arrangement effect on the electronic states of various bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) compounds composed of BEDT-TTF layers and counter-anion networks via...

Terahertz-field-induced polar charge order in electronic-type dielectrics

Ultrafast electronic-phase change in solids by light, called photoinduced phase transition, is a central issue in the field of non-equilibrium quantum physics, which has been developed very recently. In most of those phenomena, charge or spin orders in an original phase are melted by photocarrier generations, while an ordered state is usually difficult to be created from a non-ordered state by a photoexcitation. Here, we demonstrate that a strong terahertz electric-field pulse changes a Mott insulator of an organic molecular compound in κ-(ET)2Cu[N(CN)2]Cl (ET = bis(ethylenedithio)tetrathiafulvalene), to a macroscopically polarized charge-order state; herein, electronic ferroelectricity is induced by the collective intermolecular charge transfers in each dimer. In contrast, in an isostructural compound, κ-(ET)2Cu2(CN)3, which shows the spin-liquid state at low temperatures, a similar polar charge order is not stabilized by the same terahertz pulse. From the comparative studies of terahertz-field-induced second-harmonic-generation and reflectivity changes in the two compounds, we suggest the possibility that a coupling of charge and spin degrees of freedom would play important roles in the stabilization of polar charge order.

Radical cation salts of BETS and ET with dicyanamidocuprate anions demonstrating metal-insulator and semiconductor–semiconductor transitions

Electrocrystallization of bis(ethylenedithio)tetraselenafulvalene (BETS) and bis(ethylenedithio)tetrathiafulvalene (ET) in the presence of an electrolyte (Ph4P)[Cu(dca)]3⋅H2O [(dca) = N(CN)2] has been studied using different solvents. A new organic metal (BETS)2Cu(dca)3 (1), and the first radical cation salt with 3D dicyanamidocuprate anion, incorporating both diamagnetic Cu1+ and paramagnetic Cu2+atoms, (ET)2Cu1.8(dca)4 (2) have been obtained. Crystal structure, conducting properties of both salts, as well as the electronic structure of 2 and its structural analog (ET)2CuMn(dca)4 (3) were analysed. The salts 1 and 2 have layered structures. In contrast to the BETS radical cation salt 1, complex 2 is characterized by the presence of a 3D polymeric anion built into the ET radical cation layers. At ambient pressure, the resistance of the crystals 1 shows semimetal behaviour down to 30 K. Below 30 K, the resistance sharply increases and the sample becomes insulating. The application of a pressure of about 3 kbar suppresses the metal-insulator transition. The salt 2 undergoes a semiconductor I - semiconductor II phase transition, which is manifested by a jump in the resistance and a hysteresis in the R(T) curves in a very large temperature range (185 – 250 K). The phase transition is accompanied by changes in the charge state of the ET molecules, and notable structure changes in the anion layer, especially in the environment of Cu2+. For the salt 3 the calculated selfconsistent charges show upon cooling a sharp increase of charge order between 291 K and 285 K.

Interdigitated conducting tetrathiafulvalene-based coordination networks.

Assembly of a novel ethylenedithio-tetrathiafulvalene (EDT-TTF) derivative bearing two adjacent 4-thiopyridyl groups with M(NCS)2 nodes (M = Fe, Co) leads to two isostructural 1D coordination polymers showing an enhancement of their electronic conductivity by six orders of magnitude (10-6vs. 10-12 S cm-1), upon surface oxidation by iodine and subsequent generation of EDT-TTF-based radicals.

Bis(ethylenedithio)tetrathiafulvalene Cation Radical Salts Composed of Nonuniform Silver(I) Complex Polyanions.

Rational control of the molecular arrangement in solids has been the subject of intense research for many years. In particular, the structural control of bis(ethylenedithio)tetrathiafulvalene (ET) radical cations has attracted special interest because of the primary effect on the electronic properties of the salts. In this study, we obtained the first ET cation radical salts formed with nonuniform silver(I) complex polyanions, which involve multiple kinds of openings in the anionic layer, by an electrocrystallization method. θ-(ET)2Ag2(CN)[N(CN)2]2 (1) with a θ-type ET packing motif contains double helical chains composed of AgN(CN)2, whereas α″-(ET)2Ag2(CN)(SCN)2 (2) with an α″-type ET packing motif contains zigzag ladders composed of AgSCN. Both silver(I)-based tube-like assemblies are connected to each other by a cyano group, affording nonuniform polyanionic structures. Although both salts show semiconducting behavior, there is a distinct difference in their spin geometry, with an S = 1/2 Heisenberg antiferromagnetic square lattice in 1, which is associated with charge disproportionation or dynamical charge fluctuation in the ET layers, and an S = 1/2 Heisenberg anisotropic triangular lattice in 2, which results in spin frustration in the ET layers. The ability of the nonuniform polymeric structures in the anionic layers to act as templates for various arrangements of ET radical cations is demonstrated.

Synthesis and mesocrystalline properties of liquid crystal compounds with tetrathiafulvalene and two cyanobiphenyl units

ABSTRACTA series of ethylenedithiotetrathiafulvalene (EDT-TTF) compounds with cyanobiphenyl moieties attached with different length alkyl chains has been designed and synthesized. The phase behavior of these derivatives was investigated by a combination of polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction. Among the derivatives, the derivatives with spacer group lengths of n = 6–12 (3b–3d) show a distinct glassy transition during the heating and cooling processes, and 3c (n = 8) and 3d (n = 12) show liquid crystal (LC) phases below the isotropic temperature. An electrochemical study shows that the longer the spacer group, the more readily the target compound is oxidized. Density functional theory calculations show that the LC molecules are typical donor–σ-bridge–acceptor molecules.

Thermodynamic investigation by heat capacity measurements of κ-type dimer-Mott organic compounds with chemical pressure tuning

Thermodynamic discussion on the physical properties around the Mott boundary of the dimer-Mott system of [Formula: see text]-type (BEDT-TTF)2X system, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene and X denotes monovalent counter anions is performed by heat capacity measurements of the [Formula: see text]-(d[n,n] BEDT-TTF)2Cu[N(CN)2]Br of which donor molecules are partially deuterated. We compare temperature dependences of heat capacity of d[2,2], d[3,3] and d[4,4] compounds (defined as shown in Fig. 1) obtained in rapidly cooled and slowly cooled conditions. While the heat capacity of d[2,2] compound shows cooling rate dependence with the slight change of the absolute values Cp between 25 K and 50 K, the temperature dependences of the other compounds do not give drastic change by changing the cooling rate. The compounds of d[2,2] and d[3,3] located very close to the Mott boundary show peculiar hump structure in the C[Formula: see text]T[Formula: see text] that is related to the existence of a kind of lattice instability region around the first-order phase boundary. The temperature and chemical pressure dependences of the anomalous region are discussed in terms of the phase diagram in which the Mott boundary has peculiar rounding at low-temperature region.

Thermodynamic Picture of Dimer-Mott Organic Superconductors Revealed by Heat Capacity Measurements with External and Chemical Pressure Control

This article reviews and discusses the thermodynamic properties of dimer-Mott-type molecular superconductive compounds with (BEDT-TTF)2X composition, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene and X denotes counter-anions, respectively. We focus mainly on the features occurring in the κ-type structure in which the d-wave superconductive phase appears depending on the Coulomb repulsion U and the bandwidth W, which is tunable by external and chemical pressures. First, we report the high-pressure ac (alternating current) calorimetry technique and experimental system constructed to measure single-crystal samples of molecule-based compounds to derive low-temperature thermodynamic parameters. Using extremely small resistance chips as a heater and a thermometer allows four-terminal detection of an accurate temperature and its oscillation in the sample part with sufficient sensitivity. From the analyses of the temperature dependence of the ac heat capacity of κ-(BEDT-TTF)2Cu(NCS)2 under external pressures, we discuss the changes in the peak shape of the thermal anomaly at the superconductive transition temperature Tc at various external pressures p. The rather sharp peak in CpT−1 at Tc = 9.1 K with a strong coupling character at ambient pressure is gradually reduced to weaker coupling as the pressure increases to 0.45 GPa concomitant with suppression of the transition temperature. This feature is compared with the systematic argument of the chemical–pressure effect on the basis of thermal anomalies around the superconductive transition of κ-(BEDT-TTF)2X compounds and other previously studied typical dimer-Mott 2:1 compounds. Finally, the discussion is extended to the chemical pressure effect on the normal state electronic heat capacity coefficient γ obtained by applying magnetic fields higher than Hc2 and the residual γ*, which remains in the superconductive state due to the induced electron density of states around the node structure. From the overall arguments with respect to both chemical and external pressures, we suggest that a crossover of the electronic state inside the superconductive phase occurs and the coupling strength of electron pairs varies from the electron correlation region near the metal-insulator boundary to the band picture region.

Synthesis and Physical Properties of Purely Organic BEDT-TTF-Based Conductors Containing Hetero-/Homosubstituted Cl/CN-Anilate Derivatives.

Radical cation salts composed of a bis(ethylenedithio)tetrathiafulvalene (ET) donor with homo-/heterosubstituted Cl/CN anilic acids as purely organic molecular conducting materials formulated as [BEDT-TTF]2[HClCNAn] (1) and [BEDT-TTF][HCl2An] (2) have been prepared by electrocrystallization. Compounds 1 and 2 crystallized in the monoclinic space group P2/c for 1 and I2/a for 2, showing segregated donor-anion layers arranged in a α'-type donor packing pattern (1) and twisted parallel columns (2), respectively. Single-crystal conductivity measurements show that 1 is a semiconductor with room-temperature conductivity of 10-2 S cm-1 and an activation energy Ea of 1900 K.

Cyanobenzene–Ethylenedithio–Tetrathiafulvalene Salts with ClO4–: Bilayer Polymorphs and Different Stoichiometries

The electrocrystallization from dichloromethane or tetrahydrofuran solutions of the dissymmetrical bis(ethylenedithio)tetrathiafulvalene (ET) derivative cyanobenzene–ethylenedithio–tetrathiafulvalene (CNB-EDT-TTF) in the presence of perchlorate anion ClO4– affords two different polymorphs of salts with 4:1 stoichiometry, a previously described triclinic phase β″T-(CNB-EDT-TTF)4ClO4 (1a), and a new monoclinic phase β″M-(CNB-EDT-TTF)4ClO4, (1b), as well as a compound with 1:1 stoichiometry, (CNB-EDT-TTF)ClO4 (2), depending on the solvent and crystallization conditions. The special conditions necessary for the growth of the unusual 4:1 salts, requiring low current densities to oxidize the donors and subsequent slow diffusion controlled association processes, are discussed. Both 4:1 polymorphs present a bilayer structure of the donors induced by head-to-head C–N···H pairing interactions associated with a combination of R22(10) and R24(10) synthons between donors in nearby layers. These polymorphs share the sa...

New Ethylenedithio-TTF Containing a 2,2,5,5-Tetramethylpyrrolin-1-yloxyl Radical through a Vinylene Spacer and Its FeCl4− Salt—Synthesis, Physical Properties and Crystal Structure Analyses

To develop novel magnetic conductors exhibiting conducting/magnetic bifunctionalities and peculiar responses to applied magnetic fields, we synthesized new EDT-TTF (ethylenedithiotetrathiafulvalene) donor containing a 2,2,5,5-tetramethylpyrrolin-1-yloxyl radical through a π-conjugated vinylene spacer 1 and examined its electronic and crystal structures, and physical properties. We also prepared its cation radical salts by an electrochemical oxidation method and successfully cleared the crystal structures and magnetic properties of the cation radical salts, 1·FeCl4 and 1·GaCl4. These salts have strongly dimerized one-dimensional arrays of the fully oxidized donor molecules, giving rise to the formation of spin-singlet state of the π cation radical spins in the dimer. On the other hand, the FeCl4- anion locates on the side of the dimers with very short S-Cl contacts and mediates very strong π-d interaction between the donor and anion moieties, resulting in the antiferromagnetic behavior of the Weiss temperature of θ = -3.9 K through its d-π-d interaction.

First radical cаtion salt of bis(ethylenedithio)tetrathiafulvalene with organic anion [С(NCN)2NH2]–: synthesis, structure, and conducting properties

The electrochemical oxidation of bis(ethylenedithio)tetrathiafulvalene (ET) in the presence of simple dicyanamide salts of rare-earth metals with the general formula M[N(CN)2]3 (M = Gd3+, Dy3+, and Ho3+) as electrolytes was studied for the first time. A novel radicalcаtion salt α-ЕТ2[С(NCN)2NH2] with the unexpected (2,1-dicyano)guanidine anion was synthesized. The crystal structure of the salt and its conducting properties were studied. The structure of the salt is layered with alternating conducting radical-cation and insulating anionic layers. The cationic layers of the α-type are formed by two crystallographically independent radical-cations of ET of various charges. The anionic layers are formed of [С(NCN)2NH2]– anions linked by hydrogen contacts into chains. The crystals of ЕТ2[С(NCN)2NH2] demonstrate a semiconducting character of conductivity in a temperature range of 300—100 K.

Crystal structure of bis-(ethyl-enedi-thio)-tetra-thia-fulvalenium μ2-acetato-bis-[tri-bromido-rhenate(III)] 1,1,2-tri-chloro-ethane hemisolvate.

The asymmetric unit of the title salt, (C10H8S8)[Re2Br6(CH3COO)]·0.5C2H3Cl3, contains one bis-(ethyl-enedi-thio)-tetra-thia-fulvalene (ET) radical cation, one μ2-acetato-bis-[tri-bromido-rhenate(III)] anion and a 1,1,2-tri-chloro-ethane mol-ecule with half-occupancy disordered about a twofold rotation axis. The tetra-thia-fulvalene fragment adopts an almost planar configuration typical of the ET radical cation. The C atoms of both ethyl-enedi-thio fragments in the cation are disordered over two orientations with occupancy factors 0.65:0.35 and 0.77:0.23. In the anion, six Br atoms and a μ2-acetate ligand form a strongly distorted cubic O2Br6 coordination polyhedron around the Re2 dinuclear centre. In the crystal, centrosymmetrically related ET cations and Re2O2Br6 anions are linked into dimers by π-π stacking inter-actions [centroid-to-centroid distance = 3.826 (8) Å] and by pairs of additional Re⋯Br contacts [3.131 (3) Å], respectively. The dimers are further packed into a three-dimensional network by non-directional inter-ionic electrostatic forces and by C-H⋯Br and C-H⋯S hydrogen bonds. The disordered 1,1,2-tri-chloro-ethane mol-ecules occupy solvent-accessible channels along the b axis.

Ambient-Pressure Organic Superconductor κ-(ET)2Ag(CN)[N(CN)2] Formed with Polymeric Silver(I) Complex Anion

We obtained a new cation radical salt of bis(ethylenedithio)tetrathiafulvalene (ET) with a κ-type packing motif, κ-(ET)2Ag(CN)[N(CN)2], by electrooxidation. In the salt, each ET layer is separated by polymeric {Ag(CN)[N(CN)2]−}∞ layers, which are composed of Ag(I) ions trigonally coordinated to form an infinite zigzag chain of –NC–Ag–NC–Ag– with pendant dicyanamides. The salt undergoes a superconducting transition with a midpoint critical temperature (Tc) of 6.6 K and an onset Tc of 7.2 K, thereby indicating the highest Tc among ET superconductors formed with a polymeric Ag(I) complex anion.

ChemInform Abstract: Bis(vinylenedithio)tetrathiafulvalene Analogues of BEDT‐TTF

AbstractReview: synthesis and characterization; 58 refs.

Controlling superconductivity by light

In the growing field of nanotechnology, there is an interest in developing hybrid organic–inorganic devices that have controllable electrical or magnetic properties.1 Because of the nanoscale involved, the surface-to-volume ratio in these devices is large; hence, the devices can be controlled by varying their surface properties. Exerting control by using light is particularly attractive because making conventional hard electric contacts may be difficult due to size and material properties. The work of Suda et al.2 presents a device in which superconductivity is controlled by light through the excitation of a gate made from spiropyran.3 Figure 1 schematically presents the device and its mode of operation (right panel) relative to that of a common field effect transistor (left panel). Spiropyran serves as the gate and is reversibly photoisomerized from a nonionic to a zwitterionic form. In its neutral form, no field is applied to the thin single crystal of κ-(BEDT-TTF)2Cu[N(CN)2]Br (κ-Br) (BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene). Upon photoexcitation with UV light, zwitterions are formed in the spiropyran film, and as a result, holes are injected into the κ-Br, converting it to a superconductor at low temperatures. Irradiation with visible light returns the film to its neutral state.

Bis(vinylenedithio)tetrathiafulvalene analogues of BEDT-TTF.

This review aims to give an overview of the current status of our research on the synthesis of π-electron donor bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF, ET) analogues prepared from 1,8-diketones via a ring forming reaction. The new synthesized π-electron donors have vinyl moieties producing extended π-electron delocalization over the substituent phenyl rings at the peripheries.

Nonelectrochemical Synthesis, Crystal Structure, and Physical Properties of the Radical Salt [ET]2[CuCl4] (ET = Bis(ethylenedithio)tetrathiafulvalene)

The radical salt [ET]2[CuCl4] was obtained by chemical oxidation of bis(ethylenedithio)tetrathiafulvalene (ET) with the tetranuclear copper(II) halide cluster [Cu4OCl10](4-). Although a complex mixture of anions forms in solution during the redox reaction, only this product is obtained as large (>3 mm) single crystals. X-ray diffraction analysis determined that the ET molecules stack in the solid state forming dimerized 1D chains along the a axis, interleaved by [CuCl4](2-) anions. The ET dimers show very short S···S contacts (<3.41 Å). The physical properties are dominated by these intradimer ET interactions. The magnetic behavior shows antiferromagnetic coupling with a singlet-triplet gap >620 K (430 cm(-1)). The Cu(2+) (S = 1/2) centers are magnetically isolated and yield a narrow EPR line in the X-band at g = 2.01. The ET moieties are EPR silent.

Synthesis and studies of new organic conductors based on ET and EDT-TTF with the [ZnBr4]2− anions

New layer organic conductors based on bis(ethylenedithio)tetrathiafulvalene (ET)4ZnBr4Solv (Solv stands for solvent) were synthesized in various halobenzenes as solvents (C6H5X, X = Cl, Br, F and C6H4Y2, Y = Cl, Br), as well as based on ethylenedithiotetrathiafulvalene (EDT-TTF)4MBr4(1,1,2-C2H3Cl3) (M = Zn, Mn) and (EDT-TTF)9(ZnBr4)2. The crystal structure of (ET)4ZnBr4(C6H4Cl2) at room temperature was established. It was found to be composed of alternating conducting layers with various structure of stacks formed of the ET radical cations. Their conductivity and ESR spectra were measured. The ET compounds obtained are organic metals up to the temperatures of 4.2, 72, 80, or 183 K (depending on the solvent: C6H4Cl2, C6H5Cl, C6H5Br, or C6H5F, respectively); the replacement of the solvent with more bulky 1,2-dibromobenzene led to the formation of a semiconductor. The compounds (EDT-TTF)4MBr4(C2H3Cl3) with M = Zn, Mn and (EDT-TTF)9(ZnBr4)2 retain metallic character of conductivity up to the temperatures of 260, 280, and 210 K.