Thomas Roy

Trifluoromethylmetallate anions as components of molecular charge transfer salts and superconductors

Abstract Whereas polymeric and common inorganic anions frequently deprive the synthetic chemist of a chance to modify a charge transfer salt’s structure through anion alterations, discrete organometallic anions provide a vast opportunity to probe the structure/property correlations of a material through rational synthetic methods. We have recently undertaken a research effort aimed at the crystallization of conducting charge transfer salts which possess modifiable, organometallic anions as the charge compensating entities. This research has been richly rewarded with the discovery of a new family of bis(ethylenedithio)tetrathiafulvalene (BEDT–TTF or ET) based molecular superconductors. Herein is presented a summary of over 20 κ(ET) 2 M(CF 3 ) 4 (1,1,2-trihaloethane) (M=Cu, Ag, Au) superconducting salts. Three new related salts are also reported: (ET) 2 [ trans- Ag(CF 3 ) 2 (CN) 2 ], κ L (BEDT-TSF) 2 Ag(CF 3 ) 4 (TCE), and κ L (ET) 2 Ag(CF 3 ) 3 Cl(TCE).

The first organic cation-radical salt superconductor (Tc= 4 K) with an organometallic anion: superconductivity, synthesis and structure of κL-(BEDT-TTF)2Cu(CF3)4·TCE

Superconductivity at ambient pressure with onset Tc= 4.00 ± 0.05 K is reported in a unique organic cation-radical salt κL-(ET)2Cu(CF3)4·TCE, [ET = bis(ethylenedithio)tetrathiafulvalene, TCE = 1,1,2-trichloroethane] with the Cu(CF3)4– species being the first Cu3+ and F containing organometallic anion in an organic superconductor.

Synthesis and characterization of two new organic superconductors, κL- and κH-[bis(ethylenedisulfanyl)tetrathiafulvalene]2Au(CF3)4·(1,1,2-trichloroethane)via microelectrocrystallization

A novel microelectrocrystallization (MEC) procedure (ten-fold decrease in halogenated solvent use, micromolar quantities of electron donor molecule and supporting electrolyte, and Hg free electrodes), necessitated by the very small available quantities of the novel organometallic Au(CF3)4– anion, has been developed to prepare two distinct phases of κ-(ET)2Au(CF3)4·(TCE)[ET = bis(ethylenedisulfanyl)tetrathiafulvalene, TCE = 1,1,2-trichloroethane] which exhibit ambient pressure superconductivity with onset temperatures of 2.1 and 10.5 K.

Synthesen und Eigenschaften von Pentafluorethylkupfer(I)‐ und ‐(III)‐Verbindungen: Cu(C2F5) · D, [Cu(C2F5)2]– und (C2F5)2CuSC(S)N(C2H5)2

Cd(C2F5)2 · D bzw. Zn(C2F5)2 · D (D = 2 CH3CN, 2 DMF) reagieren mit Kupfer(I)halogeniden in Gegenwart von Halogeniden quantitativ zu den CuC2F5-Verbindungen CuC2F5 · D und [Cu(C2F5)2]–. Die CuC2F5-Komplexe werden NMR-spektroskopisch identifiziert, [Cu(C2F5)2]– wird als PNP-Salz (PNP = (C6H5)3PNP(C6H5)3+) isoliert. Beide Pentafluorethylkupfer(I)-Verbindungen sind bei tiefer Temperatur sehr reaktive Pentafluorethylierungs-Reagenzien. Die Oxidation von [Cu(C2F5)2]– mit [(C2H5)2NC(S)S]2 ergibt die kristalline Cu(III)-Verbindung (C2F5)2CuSC(S)N(C2H5)2 (monoklin, C2/c). Syntheses and Properties of Pentafluoroethylcopper(I) and -copper(III) Compounds: CuC2F5 · D, [Cu(C2F5)2]–, and (C2F5)2CuSC(S)N(C2H5)2 The reactions of Cd(C2F5)2 · D and Zn(C2F5)2 · D (D = 2 CH3CN, 2 DMF), respectively, with copper(I) halides in the presence of halides quantitatively yield the CuC2F5 compounds CuC2F5 · D and [Cu(C2F5)2]–. The CuC2F5 complexes are identified by NMR spectroscopy, while [Cu(C2F5)2]– is isolated as PNP salt (PNP = (C6H5)3PNP(C6H5)3+). Both compounds are excellent C2F5 group transfer reagents, even at low temperature. Oxidation of [Cu(C2F5)2]– with [(C2H5)2NC(S)S]2 yields the crystalline Cu(III) compound (C2F5)2CuSC(S)N(C2H5)2 (monoclinic, C2/c).

New Organic Superconductors in the System (ET)2M(CF3)4(Solvent) (M = Cu, Ag, Au): Dramatic Effects of Organometallic Anion and Solvent Replacement

Abstract Over twenty molecular-based superconductors have been synthesized recently via electrocrystallization of the organic bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) electron donor molecule with the novel organometallic M(CF3)4 − (M = Cu, Ag, and Au) anions in a variety of 1,1,2-trihaloethane solvents. The highly anisotropic physical properties of these solvated (ET)2 M(CF3)4(1,1,2-trihaloethane) salts can be tuned via modifications of each of their three discrete molecular components. These unique salts crystallize in two distinct structural modifications of the κ-type packing motif (sheets of dimerized electron-donor molecules arranged in a parquet fashion). Crystals of the lower T c phase (κL) have a plate-like morphology and superconducting transition temperatures in the 2–6 K range, while the transitions of the higher T c phase (κH), which typically have a needle-like morphology, are in the 9–11 K range. The synthesis, structure, and physical properties of this new family of materials ...

New ET-based organic superconductors with the organometallic anion Cu(CF3)4-

Abstract Electrocrystallization of bis(ethylenedithio)tetrathiafulvalene (ET) with (PNP)Cu(CF 3 ) 4 in 1,1,2-trichloroethane (TCE) results in two new superconductors, κ L -(ET) 2 Cu(CF 3 ) 4 ·(TCE), 1 , with T c = 4.0 K, and κ H -(ET) 2 Cu(CF 3 ) 4 ·(TCE) x , 2 , with T c = 9.2 K. 1 forms well-developed plate-like crystals whose structure was determined by X-ray crystallography. Its band electronic structure is reported. The κ H -phase forms long, thin needle bundles.

Esr studies of two new organic superconductors: β″-(BEDT-TTF)2SF5CH2CF2SO3 and κL′-(BEDT-TTF)2Cu(CF3)4(DBCE)

Abstract The normal-state ESR properties of two new organic superconductors, β″-(BEDT-TTF) 2 SF 5 CH 2 CF 2 SO 3 and κ L ′-(BEDTTTF) 2 Cu(CF 3 ) 4 (DBCE) are reported. Both compounds showed metallic properties below 140 K. The former gave ESR line widths and g -values of 23 to 34 G and 2.004 to 2.012, respectively. The latter gave line widths and g -values of 45 to 58 G and 2.006 to 2.012, respectively. The orientation-dependent line widths and g -values of the κ L ′-phase were found to be similar to that of the κ-(ET) 4 Hg 3 Br 8 but not to the κ L -phases in general.

Rational design of organic superconductors through the use of the large, discrete molecular anions M(CF3)4-(M = Cu, Ag, Au) and SO3CF2CH2SF5-

A new approach to the synthesis of organic superconductors has recently been pioneered which involves the use of large, discrete, molecular anions as the charge-compensating entities in these charge transfer salts. The organic electron-donor molecule bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) has been electrocrystallized with the novel organometallic M(CF3)4 (M = Cu, Ag, and Au) anions in a variety of 1,1,2-trihaloethane solvents. Over twenty organic superconductors have been synthesized which can be described by the general formula (ET) 2 M(CF 3 ) 4 (1,1,2-trihaloethane). These solvated salts are shown to have highly anisotropic physical properties which can be tuned via modifications of each of their three molecular components: ET electron donor molecule, M(CF3)4 anion, and neutral 1,1,2-trihaloethane solvent molecule. Superconductivity has also been observed in an ET salt containing the discrete SF 5 CH 2 CF 2 SO 3 - anion with an onset temperature near 5.2 K.

Polymorphism in κ-(BEDT-TTF)2M(CF3)4(solvent) superconductors

Abstract A new crystallographic modification (κ L ′) was found in the BEDT-TTF: M (CF 3 ) 4 − :solvent ( M = Cu, Ag, Au) system. The structure of monoclinic κ L ′-(BEDT-TTF) 2 Cu(CF 3 ) 4 (1,2-dibromo-1-chloroethane = DBCE) is reported. It differs from the orthorhombic κ L − phase by having all BEDT-TTF molecules tilted in the same direction with respect to the conducting plane normal, whereas in κ L the tilt direction alternates between layers.

Thermodynamic properties of the organic superconductor κL-(ET)2Ag(CF3)4·TCE

Abstract We present specific-heat, magnetization, and ac-susceptibility measurements of the recently discovered organic superconductor κL-(ET)2Ag(CF3)4·TCE, where ET (= BEDT-TTF) stands for bisethylenedithio-tetrathiafulvalene and TCE is the neutral solvent 1,1,2-trichloroethane. We observed a very large anisotropy of the critical field B ∗ extracted from ac-susceptibility data in accord with the enhanced ET-layer separation due to the large anions. The strong frequency dependence of B ∗ reveals the weak pinning forces in the material. Magnetization and specific-heat, C, measurements prove the bulk effect of superconductivity. The linear coefficient of C is γ ≈ 50 mJ/molK2 which is a factor 9 larger than expected from a free-electron picture. Indications for strong coupling are found.