Ethylenedithio Tetrathiafulvalene Salts Research Articles

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.

Many-body effect on the superconducting transition temperature in layered organic superconductors

We have calculated bare cyclotron masses of layered organic superconductors, $\ensuremath{\kappa}$-type bis(ethylenedithio)tetrathiafulvalene (ET) and bis(ethylenedithio)tetraselenafulvalene (BETS) salts, in which the effective cyclotron masses have been determined by quantum oscillations. The higher superconducting transition temperature $({T}_{c})$ materials show the larger ratios of the observed to the bare cyclotron masses. This indicates that the mass enhancement, i.e., strong many-body effect is quite important for a high-${T}_{c}$ organic superconductor. The $\ensuremath{\kappa}$-type BETS salts need a stronger many-body interaction than the ET salts to be a superconductor, and the magnetic exchange interaction with magnetic anions realizes this requirement.

The search for new superconductors at argonne national laboratory

The organic superconductors program at Argonne National Laboratory was started by Jack M. Williams in 1981. Initial studies centered around structural effects in the TMTSF salts. Since 1984, the major emphasis has been on salts of the electron donor bis(ethylenedithio)tetrathiafulvalene (ET). Important milestones include the discovery of a number of new superconductors, among them: β-(ET) 2 IBr 2 (T c =2.8 K) and β-(ET) 2 AuI 2 (T c =4−5 K). These salts led to the first structure-properties relationship in ET salts. κ-(ET) 2 Cu[N(CN) 2 ]Br (T c =11.8 K, ambient pressure) and κ-(ET) 2 Cu[N(CN) 2 ]Cl (T c =12.5 K at 0.3 kbar pressure) are still the cation radical superconductors with the highest known transition temperatures. The families of κ L - and κ H -(ET) 2 [M(CF 3 ) 4 ](solvent) salts (T c =2−11 K) yielded at least 25 new closely related organic superconductors with M=Cu, Ag, Au, and solvent=1,1,2-trihaloethane. β″-(ET) 2 SF 5 CH 2 CF 2 SO 3 (T c =5 K) was the first superconductor where both the radical cation and the charge balancing anion were organic. Recent results in the synthesis and characterization of ET salts with anions similar to SF 5 CH 2 CF 2 SO 3 − are presented.

Syntheses and Crystal Structures of ET and BETS Salts Containing Bis(dithiosquarato)metalate Anions

Abstract A series of cation radical salts of bis(ethylenedithio)tetrathiafulvalene (ET) and bis(ethylenedithio)tetraselenafulvalene (BETS) as donors and bis(dithiosquarato)metalate ([M(dts)2]n−) as anions were synthesized. The electrical resistivities of most of these salts ((BETS)2[Pd(dts)2] (1), (BETS)2[Pd(dts)2]·2(1,1,2,2-TCE) (2) (1,1,2,2-TCE = 1,1,2,2-tetrachloroethane), (BETS)[Au(dts)2] (4), (ET)2[Pd(dts)2] (5), (ET)2[Pt(dts)2] (6), and (ET)[Au(dts)2] (7)) were semiconductive. However, one of the BETS salts with [Pd(dts)2], whose donor : anion ratio was 5 : 1. (BETS)x[Pd(dts)2] (x ≈ 5.0) (3), showed a metallic behavior down to 4 K. Although the crystal structure of these semiconducting salts was a kind of mixed stacks, many short contacts within the sum of the van der Waals radii were seen between chalcogens of the donors, and between chalcogens of the donor and anion. In addition, four terminal oxygen atoms of bis(dithiosquarato)metalate anion had C–H···O hydrogen bonds with terminal ethylene groups of ET and BETS, which was one of the factors determining the conformation of the terminal ethylene groups in these crystals.

First salt of bis(ethylenedithio)tetrathiafulvalene containing mono- and dications

The radical-cation salts of bis(ethylenedithio)tetrathiafulvalene (ET) hold interest since many of these species are organic metals and some are superconductors [i, 2]. We have synthesized a series of salts of ET with metal complex anions, (MX~) =-, where M = Zn, Mn, Co, and Cd and X = CI, Br having different physical properties. Among these compounds, we have found the salt (ET)3(ZnCI~) 2, which holds interest not so much for its physical properties but in light of the circumstance that it contains the previously undescribed ET 2+ dication. Crystals of this salt were obtained by the electrochemical oxidation of 0.002 mole/liter ET in benzonitrile on a platinum anode using direct current of 2 ~A at 80~ We used 0.005 mole/liter (Bu4N)2(ZnCI~) as the electrolyte.