Series Of Molecular Conductors Research Articles

Molecular conductors from bis(ethylenedithio)tetrathiafulvalene with tris(oxalato)rhodate.

This article reports a family of new radical-cation salts of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) with tris(oxalato)rhodate: three salts with the formula β''-(BEDT-TTF)4[(cation)Rh(C2O4)3]·solvent (solvent = fluorobenzene, chlorobenzene, or bromobenzene) and one with the formula pseudo-κ-(BEDT-TTF)4[(NH4)Rh(C2O4)3]·benzonitrile. We report here the syntheses, crystal structures, electrical properties and Raman spectroscopy of these new molecular conductors. The bromobenzene salt shows a decrease in resistivity below 2.5 K indicative of a superconducting transition and a Shubnikov-de Haas oscillation with a frequency of 232 T and effective mass m* of 1.27me.

The Series of Molecular Conductors and Superconductors ET4[AFe(C2O4)3]·PhX (ET = bis(ethylenedithio)tetrathiafulvalene; (C2O4)2–= oxalate; A+= H3O+, K+; X = F, Cl, Br, and I): Influence of the Halobenzene Guest Molecules on the Crystal Structure and Superconducting Properties

An extensive series of radical salts formed by the organic donor bis(ethylenedithio)tetrathiafulvalene (ET), the paramagnetic tris(oxalato)ferrate(III) anion [Fe(C(2)O(4))(3)](3-), and halobenzene guest molecules has been synthesized and characterized. The change of the halogen atom in this series has allowed the study of the effect of the size and charge polarization on the crystal structures and physical properties while keeping the geometry of the guest molecule. The general formula of the salts is ET(4)[A(I)Fe(C(2)O(4))(3)]·G with A/G = H(3)O(+)/PhF (1); H(3)O(+)/PhCl (2); H(3)O(+)/PhBr (3), and K(+)/PhI (4), (crystal data at room temperature: (1) monoclinic, space group C2/c with a = 10.3123(2) Å, b = 20.0205(3) Å, c = 35.2732(4) Å, β = 92.511(2)°, V = 7275.4(2) Å(3), Z = 4; (2) monoclinic, space group C2/c with a = 10.2899(4) Å, b = 20.026(10) Å, c = 35.411(10) Å, β = 92.974°, V = 7287(4) Å(3), Z = 4; (3) monoclinic, space group C2/c with a = 10.2875(3) Å, b = 20.0546(15) Å, c = 35.513(2) Å, β = 93.238(5)°, V = 7315.0(7) Å(3), Z = 4; (4) monoclinic, space group C2/c with a = 10.2260(2) Å, b = 19.9234(2) Å, c = 35.9064(6) Å, β = 93.3664(6)°, V = 7302.83(18) Å(3), Z = 4). The crystal structures at 120 K evidence that compounds 1-3 undergo a structural transition to a lower symmetry phase when the temperature is lowered (crystal data at 120 K: (1) triclinic, space group P1 with a = 10.2595(3) Å, b = 11.1403(3) Å, c = 34.9516(9) Å, α = 89.149(2)°, β = 86.762(2)°, γ = 62.578(3)°, V = 3539.96(19) Å(3), Z = 2; (2) triclinic, space group P1 with a = 10.25276(14) Å, b = 11.15081(13) Å, c = 35.1363(5) Å, α = 89.0829(10)°, β = 86.5203(11)°, γ = 62.6678(13)°, V = 3561.65(8) Å(3), Z = 2; (3) triclinic, space group P1 with a = 10.25554(17) Å, b = 11.16966(18) Å, c = 35.1997(5) Å, α = 62.7251(16)°, β = 86.3083(12)°, γ = 62.7251(16)°, V = 3575.99(10) Å(3), Z = 2; (4) monoclinic, space group C2/c with a = 10.1637(3) Å, b = 19.7251(6) Å, c = 35.6405(11) Å, β = 93.895(3)°, V = 7128.7(4) Å(3), Z = 4). A detailed crystallographic study shows a change in the symmetry of the crystal for compound 3 at about 200 K. This structural transition arises from the partial ordering of some ethylene groups in the ET molecules and involves a slight movement of the halobenzene guest molecules (which occupy hexagonal cavities in the anionic layers) toward one of the adjacent organic layers, giving rise to two nonequivalent organic layers at 120 K (compared to only one at room temperature). The structural transition at about 200 K is also observed in the electrical properties of 1-3 and in the magnetic properties of 1. The direct current (dc) conductivity shows metallic behavior in salts 1-3 with superconducting transitions at about 4.0 and 1.0 K in salts 3 and 1, respectively. Salt 4 shows a semiconductor behavior in the temperature range 300-50 K with an activation energy of 64 meV. The magnetic measurements confirm the presence of high spin S = 5/2 [Fe(C(2)O(4))(3)](3-) isolated monomers together with a Pauli paramagnetism, typical of metals, in compounds 1-3. The magnetic properties can be very well reproduced in the whole temperature range with a simple model of isolated S = 5/2 ions with a zero field splitting plus a temperature independent paramagnetism (Nα) with the following parameters: g = 1.965, |D| = 0.31 cm(-1), and Nα = 1.5 × 10(-3) emu mol(-1) for 1, g = 2.024, |D| = 0.65 cm(-1), and Nα = 1.4 × 10(-3) emu mol(-1) for 2, and g = 2.001, |D| = 0.52 cm(-1), and Nα = 1.5 × 10(-3) emu mol(-1) for 3.

An approach to the origin of transport properties in a series of molecular conductors, based on XPS and spectroscopic studies

An approach to the origin of transport properties in a series of molecular conductors, based on XPS and spectroscopic studies

An Approach to the Origin of Transport Properties in a Series of Molecular Conductors, Based on XPS and Spectroscopic Studies

X-ray Photoelectron Spectroscopy and Raman spectroscopy are combined to evaluate the stoichiometry and charge state of building units in conductive films containing TTF, ET or TMTSF donors and [Ni(dmit)2] or [M(dcbdt)2] acceptors.

Effect of Hydrostatic Pressure on Molecular Conductors, Pd(dmit) 2 Salts

A series of molecular conductors β′-( cation)[Pd(dmit) 2] 2 ( cation = Et 2Me 2 P and Me 4P) exhibit various complicated pressure-induced phenomena. Resistivity measurements under high pressure up to 8 GPa have been carried out using a clamp-type piston-cylinder cell and cubic anvil type high pressure apparatus. The Et 2Me 2P salt shows non-metallic phases at low and high pressure regions, between which a metallic phase appears. The application of pressure suppresses the low-temperature resistivity of this salt. However, the non-metallic behavior still remains at low temperature under 8 GPa. For the Me 4P salt, the metal-to-non-metal transition temperature reaches a minimum at 0.83 GPa and turns to increase with increasing pressure up to 8 GPa, showing no metallic state stable at low temperature

Low Temperature Electronic States of B′-Type Pd(dmit)2 Compounds

Magnetic resonance investigations of metal dithiolene complexes, β′-R 4Z[Pd(dmit)2]2, have been performed. Although they are isostructural with little differences in lattice parameters, their spin-spin correlation and antiferromagnetic transition temperature, T N, show huge sample dependence. We found a close relationship between the T N and inter-dimer interactions. The low temperature electronic states of a series of molecular conductors based on Pd(dmit)2 at ambient pressure are discussed from microscopic points of view.

Novel electronic states in the (DCNQI) 2Cu system

A series of molecular conductors (R 1,R 2-DCNQI) 2Cu exhibit unique physical properties associated with the interaction between the pπ organic one-dimensional band and the d-orbital of Cu atom. The DCNQI-Cu salts are classified into three types: type I salt shows a metallic behavior down to low temperature, type II salt shows a metal-insulator (M-I) transition, and type III salt shows a M-I-M (reentrant) transition. All the types of transitions are first-order. In addition, the DI-system (R 1=R 2=I) shows another metallic phase accompanied by the small resistivity anomaly in the higher-pressure region. There are two important parameters that govern the electronic states of this system. The one is the amount of charge transfer from Cu to DCNQI which is quite sensitive to pressure or substituent (R 1,R 2). The other parameter is an inter-chain LUMO···LUMO interaction which plays an important role in the iodine-containing system. This interaction significantly affects the electronic structure. A complicated P-T phase diagram of the DI-system could be explained by these two parameters.

(DCNQI)2Cu: Variety of Magnetism Arising from pπ-d Interactions

Abstract Recent advances of our study of magnetic properties of a series of molecular conductors, Cu salts of DCNQIs, are presented. First, we have found weak ferromagnetism in the antiferromagnetically ordered state of Cu spins in the insulating phase. Second, the metal-insulator (M-I) transitions of these systems have been characterized by the abrupt change of Cu 3d spins from the itinerant state to the completely localized state, even in the metal-insulator-metal (M-I-M) reentrant system, (DMe-DCNQI-α,α'-d 2)2Cu. Finally, (DI-DCNQI)2Cu is found to exhibit enhanced and temperature dependent susceptibility, suggesting the effect of spin fluctuations of itinerant electrons in a Cu 3d narrow band.

Magnetic properties of DCNQI-Cu systems

Abstract Recent advances in the study of magnetic properties of a series of molecular conductors, Cu salts of DCNQIs, are presented. First, the antiferromagnetic order of Cu spins in the insulating phases below about 10 K is found to be accompanied by weak ferromagnetism with the spontaneous moment perpendicular to the tetragonal c -axis. Second, our susceptibility study of the metal-insulator-metal (M-I-M) reentrant system, (DMe-DCNQI-α,α′- d 2 ) 2 Cu, has lead to the absence of many-body enhancement of the susceptibility in the low temperature metallic phase. Finally, (DI-DCNQI) 2 Cu is found to exhibit considerably enhanced and temperature dependent susceptibility, suggesting the effect of spin fluctuation in the metallic state.