BEDT-TTF Charge Transfer Salts Research Articles

BEDT-TTF Tris(oxalato)germanate(IV) Salts with Novel Donor Packing Motifs

Abstract The synthesis, crystal structure, and conducting properties of two new BEDT-TTF charge-transfer salts containing tris(oxalato)germanate(IV) anions are described. (BEDT-TTF)5[Ge(C2O4)3]2 (1) crystallizes in the monoclinic space group C2, a = 23.0994(11) Å, b = 11.0200(5) Å, c = 19.5455(9) Å, β = 117.628(4)°, V = 4408.1(4) Å3, T = 120(2) K, Z = 2, R1 = 0.0659 [F2 > 2σ(F2)]. Compound 2 (BEDT-TTF)7[(Ge(C2O4)3]2·0.87CH2Cl2·0.09H2O crystallizes in the monoclinic space group C2/c, a = 37.081(2) Å, b = 11.5449(7) Å, c = 28.6415(13) Å, β = 93.7767(9)°, V = 12234.8(12) Å3, T = 293(2) K, Z = 4, R1 = 0.0834 [F2 > 2σ(F2)]. Electrical resistivity measurements show that 1 and 2 are both semiconductors.

Multi-layered molecular charge-transfer salts containing alkali metal ions

The synthesis, crystal structure and physical properties of two new BEDT-TTF charge-transfer salts containing the tris(oxalato)ferrate(III) anion are described. The most commonly found tris(oxalato)metallate(III) salts of BEDT-TTF contain alternating layers of BEDT-TTF cations and tris(oxalato)metallate anions, but the two salts reported here are multi-layered structures. Compound I is of the type ABCDABCDA as observed previously in the proton-conducting compound β″-(BEDT-TTF)4[Fe(C2O4)3]2·18-crown-6·9HxO and the alpha–beta family of salts α,β″-(BEDT-TTF)4[(NH4)Ga/Fe(C2O4)3]·G (G = PhN(CH3)COH, PhCH2CN and PhCOCH3). In α‴-(BEDT-TTF)9[Fe(C2O4)3]8Na18(H2O)24 (I) the A layers consist of only BEDT-TTF, B/D layers consist of tris(oxalato)ferrate(III) and sodium, and the C layers consist of sodium and water. In α-(BEDT-TTF)10(18-crown-6)6K6[Fe(C2O4)3]4(H2O)24 (II) the packing is of a type not seen before, ABCBABCBA. The A layers in II consist of only BEDT-TTF, B layers consist of tris(oxalato)ferrate(III), potassium, water and 18-crown-6, and C layers consist of 18-crown-6, potassium and water. Both salts are semiconductors between room temperature and 140 K.

Spectroscopic investigations of the BEDT-TTF charge transfer salts with NO 3− anions (β″- and δ-phase)

We report the polarized reflectance spectra (650–6500 cm −1) as well FT-NIR Raman spectra of β″-(BEDT-TTF) 3(NO 3) 2 and δ-(BEDT-TTF) 2(NO 3) 0.9(NO 2) 0.1 salts as a function of temperature. Additionally, the crystal structure of δ-phase salt was determined at room temperature and the temperature dependence of electrical conductivity was measured. The reflectance spectra of metallic β″-phase salt were fitted with the Drude model; the metal–insulator transition at T = 20–27 K has practically no influence on IR spectra. The δ-phase salt shows semiconducting behavior; inside conducting organic layers the BEDT-TTF molecules are arranged in dimers. The specific vibrational features of the δ-salt are discussed in terms of hydrogen bonding between BEDT-TTF and anions.

BEDT–TTF charge-transfer salts: new structures, new functionalities

In the continuing search for new physical properties and combinations of properties in molecular materials, novel phenomena and structures are identified in three categories of TTF and BEDT–TTF (bis-ethylenedithiotetrathiafulvalene) charge-transfer salts with inorganic complex anions. When the anion is a 3d complex containing NCS – and an aromatic donor, long range π–d ferrimagnetic order is established by donor-anion π–π overlap; when the anion is a tris-oxalato-metallate(III) complex, both normal state and superconducting behaviour are dramatically influenced by changing guest molecules in the lattice, while incorporating columns of crown ether and H 3O +/H 2O leads to metallic conductors that simultaneously transport protons. To cite this article: P. Day, C. R. Chimie 6 (2003).

New Molecular Charge Transfer Salts of BEDT-TTF, Bis(ethylenedithio) Tetrathiafulvalene, with Thiocyanato-Complex Anions: (BEDT-TTF)4[Fe(NCS)6]·CH2Cl2 and (BEDT-TTF)2[Cr(NCS)4(bipym)]·0.15H2O

Two new charge transfer salts of BEDT-TTF, bis (ethylenedithio) tetrathiafulvalene, with thiocyanato-metal complex anions have been synthesized and characterized as (BEDT-TTF)4[Fe(NCS)6]·CH2Cl2 and (BEDT-TTF)2[Cr(NCS)4 (bipym)]·0.15H2O, where bipym=2,2′-bipyrimidine. The Fe salt, I, crystallizes in the P-1 (No. 2) space group at 150 K with a=10.629(1) Å, b=12.099(1) Å, c=16.062(2) Å, α=99.61(1)°, β=90.87(1)°, γ=112.92(1)°, and V=1868.5(6) Å3. At 150 K the Cr salt, II, crystallizes in the P-1 (No. 2) space group with a=9.243(2), b=11.781(2), c=22.925(5) Å, α=93.76(3), β=101.51(3), γ=105.45(3)°, V=2339.0(8) Å3, and Z=2. Both salts exhibit close S···S contacts between the anion and cation components and in II there is no π-stacking between the bipym group and the BEDT-TTF molecules. Both salts are paramagnetic with C=4.926 I and C=1.819 II with small negative Weiss constants of −0.19 and −0.26, respectively. Therefore, the S···S contacts alone do not promote correlated magnetic effects as seen in other thiocyanato salts that also contain π-stacking. Each compound is a semiconductor and has two crystallographically independent BEDT-TTF molecules for which bond length analysis give charges of +0.9±0.1/+0.6±0.1 for I and +0.3±0.1/+0.9±0.1 for II.

Novel charge transfer salts of BEDT-TTF with metal oxalate counterions

The preparation, crystal structures and properties of three new BEDT-TTF, bis(ethylenedithio)tetrathiafulvalene, (ET for short), charge transfer salts beta (ET)(4).[(H3O)Cr(C2O4)(3)].C6H5NO2 I, beta (ET)(4).[(H3O)Fe(C2O4)(3)].C6H5NO2 II and (ET)(4). Fe-2(C2O4)(5)] III are reported. The structures of I and II consist of alternating layers of ET and an approximately hexagonal network formed by H3O+ and the metal with the solvent molecule, C6H5NO2, occupying hexagonal cavities in the anion layer. Both C6H5NO2 salts are superconducting, the iron salt having a T-c of 6.2 K and the chromium salt having a T-c of 5.8 K. The structure of(ET)(4)Fe-2(C2O4)(5)] consists of an iron oxalate bridged dimer, (Fe-Fe distance 5.472 Angstrom), interspersed with ET in a checker board arrangement. It is monoclinic and crystallises in the P2(1)/n space group. At 150 K a = 16.8068 (3) Angstrom, b = 10.9556 (2) Angstrom, c = 19.4109 (3) Angstrom, beta = 102.1593 (9) degrees and V = 3493.92 (10) Angstrom (3). Squid measurements show short range antiferromagnetic ordering.

Sulfur K-edge X-ray absorption spectra for BETS and BEDT-TTF charge transfer salts: a novel probe for the determination of hole concentration

High-resolution linearly polarized S K-edge X-ray absorption spectra for charge-transfer salts, λ-(BETS) 2GaCl 4 and β-(BEDT-TTF) 2PF 6 (BETS: bis(ethylenedithio)tetraselenafulvalene; BEDT-TTF: bis(ethylenedithiolo)tetrathiafulvalene) have been measured using undulator radiation. For both the compounds, weak bands below the most intense σ ∗ transition are found. These characteristic bands are absent for the corresponding neutral compounds, BETS and BEDT-TTF. They are assigned to the transition to the highest occupied molecular orbital based on linear polarization dependence. These bands are proposed as a novel probe for determination of the hole concentration in the charge-transfer salts containing BETS and BEDT-TTF analogues.

Electrodynamics of quasi-two-dimensional BEDT-TTF charge transfer salts

We consider the millimeter-wave electrodynamics specific to quasi-two-dimensional conductors and superconductors based on the organic donor molecule BEDT-TTF. Using realistic physical parameters, we examine the current polarizations that result for different oscillating (GHz) electric and magnetic-field polarizations. We show that, in general, it is possible to discriminate between effects (dissipation and dispersion) due to in-plane and interlayer ac currents. However, we also show that it is not possible to selectively probe any single component of the in-plane conductivity tensor, and that excitation of interlayer currents is strongly influenced by the sample geometry and the electromagnetic field polarization.

TTF based charge transfer salts of [M(NCS)4(C9H7N)2]− where M = Cr, Fe and C9H7N = isoquinoline; observation of bulk ferrimagnetic order

Three new charge transfer salts of BEDT-TTF and TTF with the counter ions [M(NCS)4(C9H7N)2]− (M = Cr, Fe; C9H7N = isoquinoline) are described. The materials are prepared by standard electrocrystallisation techniques. The nature of the anion is verified in the crystal structure of the salt [C9H8N][Cr(NCS)4(C9H7N)]·C12H24O6·H2O which is used as the electrolyte when M = Cr. All of the charge transfer salts display long range ferrimagnetic order originating from the interaction between M (S = 3/2 or S = 5/2) and the donor (S = 1/2). The measured critical temperatures are 4.2 K (BEDT-TTF, M = Cr), 4.5 K (BEDT-TTF, M = Fe) and 8.9 K (TTF, M = Cr). Each of the compounds also shows a modest magnetic hysteresis of 338, 18 and 75 Oe for BEDT-TTF salts of M = Cr, Fe and the TTF salt of Cr, respectively.

Anion-cation interdependency in bedt-ttf charge transfer salts of [M III(C 2O 4)] 3−

Metal(III)tris(oxalate) charge transfer salts of bis(ethylenedithio)tetrathiafulvalene, bedt-ttf, display a rich variety of magnetic and conducting properties. The series contains both semiconductors and the first molecular superconductor containing paramagnetic d electrons. Most of the compounds in the series follow the general formula (bedt-ttf) 4M(C 2O 4) 3. A.solvent (M = metal(III); A = K +, NH 4 + or H 2O). The conducting properties arise from different arrangements of the bedt-ttf molecules; packing motifs, conformational changes and charge distribution. We examine how changes in the oxalate co-ordination mode can promote specific donor packing motifs.

A periodic density functional study of BEDT–TTF salts†

We report the first ab initio computational study of the structural and electronic properties of BEDT–TTF charge transfer salts, which have wide ranging physical properties which are derived primarily from the packing of the donor-radical cations. The calculations accurately reproduce the observed crystal structure of the material and provide new information on the electronic structure of the (BEDT-TTF)[FeBr4] salt.

Crystal structures and physical properties of BEDT-TTF charge transfer salts with (Mo 6 Cl 8 )X 2- 6 anions (BEDT-TTF = bis(ethylenedithio)-tetrathiafulvalene; X=Cl, Br)

The crystal structures of three charge transfer salts of BEDT-TTF (bis(ethyl-enedithio)tetrathiafulvalene) with metal cluster anions [Mo6Cl8]X2-6 (X = Cl, Br) are reported, together with their electrical conductivity and magnetic properties. g4[Mo6Cl8]Br6-2THF is triclinic P1, a 9.690(2), b 12.540(5), c A, n 92.89(2)°, Z = 1 and isostructural with the corresponding X = Cl salt. Both salts show metal-insulator transitions, at 190 and 265 K, respectively. (BEDT-TTF)4[Mo6Cl8]Cl6.2CH2Cl2 is triclinic P1, a 10.290(1), b 12.877(1), c 18.024(3) A, n 91.50(1)°, Z = 1 and likewise undergoes a metal-insulator transition, at 60 K. Though the BEDT-TTF packing mode is also g , the symmetry of the stacks is different. f -(BEDT TTF)4[Mo6Cl8]Cl6.2DMF is monoclinic P21/n, a 9.676(9), b 10.20(1), c 43.37(5)°, Z =2. It is semiconducting due to charge localization within the BEDT-TTF layer.

Magnetic molecular semiconductors and superconductors: BEDT-TTF tris-oxalato-metallate(III) salts

Making new compounds that combine different physical properties in the same crystal lattice is a significant goal for chemists working on synthetic metals. As part of our ongoing programme to synthesise molecular conductors containing embedded magnetic moments we have investigated charge transfer salts of BEDT-TTF with tris-oxalatometallate (III) ions M(C 2O 4) 3 3− (M = Cr, Fe). The series (BEDT-TTF) ×[AM(C 2O 4) 3] y(C 6H 5CN) z is especially rich and interesting since it contains semiconductors (A = K, NH 4; M = Cr, Fe) and the first molecular superconductor containing paramagnetic ions (A = H 2O; M = Fe; x = 4, y = z = 1). The steric and charge factors determining the geometry of cation and anion layers in these compounds are surveyed, as well as the relation between the crystal structures and physical properties.

Calculations of quantum oscillations in quasi-two-dimensional charge-transfer salts

A numerical model is used to derive the quantum oscillations in the magnetisation and magnetoresistance of quasi-two-dimensional α-phase BEDT-TTF charge-transfer salts in high magnetic fields. Recent experimental results are simulated and the standard Lifshitz-Kosevich formalism is shown to be no longer appropriate.

Quasi-one-dimensional bis(ethylenedithio)tetrathiafulvalene charge- transfer salts with paramagnetic Group 6 anions

C. J. Kepert, M. Kurmoo, M. R. Truter and P. Day, J. Chem. Soc., Dalton Trans., 1997, 607 DOI: 10.1039/A606025K

OVERVIEW OF ORGANIC SUPERCONDUCTORS

Organic materials which are usually used for insulators, were shown to be an electrical conductor by H. Akamatsu, H. Inokuchi, and Y. Matsunaga in 1954. Moreover, J.P. Ferraris et al. showed that TTF [center dot] TCNQ was stably metallic down to around 60 K in 1973. Because of a low dimensionality of organic compound, however, a stabilization of an electronic state and a destabilization of a periodic lattice constructed a charge density wave which led a metal-insulator transition (a Peierls transition). After overcoming this low dimensionality, D. Jerome et al. discovered the first organic superconductor, (TMTSF)[sub 2] PF[sub 6] ([Tc] = 0.9 K (12kbar)) in 1980. Then with the resisting up of [Tc] constantly, the superconductor [kappa]-(BEDT-TTF)[sub 2](NCS)[sub 2] ([Tc] = 10.4 K) was found in 1987 and the [Tc] of [kappa]-(BEDT-TTF)[sub 2]Cu[N(CN)[sub 2]]Cl, 12.8 K at 0.3kbar, is the highest among the TTF family. Moreover, when the authors included the C[sub 60] system is included as molecular superconductor, the [Tc] = 33 K of Cs[sub 2]RbC[sub 60] reaches the starting point of oxide superconductors. In this paper, the history of organic conductors is described in Sec. 2. In Sec. 3, the author chooses the typical example of organic superconductor,more » [kappa]-(BEDT-TTF)[sub 2]Cu(NCS)[sub 2], and the preparation, crystal structure, chemical and physical properties are reviewed. In Sec. 4, the mechanism of organic superconductors is discussed and the future of organic superconductors is finally presented. 118 refs.« less