New BETS Conductors with Magnetic Anions (BETS = bis(ethylenedithio)tetraselenafulvalene)

Abstract

The preparation, crystal structures, and electric and magnetic properties of (BETS)2MX4 molecular conductors (BETS = bis(ethylenedithio)tetraselenafulvalene; M = Mn2+, Fe3+, Co2+, Ni2+, Cu2+; X = Cl, Br, CN) are reported. Resistivity measurements down to 2 K reveal the coexistence of the BETS π conduction electrons and the localized magnetic moments of the anions in the κ-(BETS)2FeCl4 and κ-(BETS)4(CoCl4)(C2H3Cl3) salts. Another FeCl4 phase, λ-(BETS)2FeCl4, undergoes a sharp metal-insulator (MI) transition around 8 K. At the same temperature, a magnetic transition of the FeCl4-anions takes place cooperatively. A superconducting transition is observed at 4.6 K in λ-(BETS)2(FeCl4)0.5(GaCl4)0.5, where half of the anion sites are occupied by magnetic ions. The crystals prepared from 1,1,2-trichloroethane solutions with the NiCl4 2- and MnCl4 2- anions exhibit the behavior of a semimetal down to ≈100 K. The (BETS)4(Cu2Cl6) salt remains metallic down to 4.2 K. ESR studies show that the Fe3+ ions in κ- and λ-(BETS)2FeCl4 are in a high-spin state. The temperature dependencies of the spin susceptibilities of κ- and λ-(BETS)2FeCl4 indicate antiferromagnetic interactions between the Fe3+ ions. The crystal structure analyses of κ- and λ-(BETS)2FeCl4 have been carried out at 298 and 10 K. Closer BETS···FeCl4 contacts in λ-(BETS)2FeCl4 are observed, which is consistent with the larger Weiss temperature of this compound.

Hydrogen bond-promoted metallic state in a purely organic single-component conductor under pressure

“…3b). They were obtained by the extended Hückel method calculations [40][41][42] . Figure 4a,b show the electronic band structure consisting of four independent HOMOs for j-S and j-Se, respectively.…”

Antiferromagnetic Ordering in Organic Conductor λ-(BEDT-TTF)2GaCl4 Probed by 13C NMR

“…Although the arrangements of the dimers are different from each other, the overlap characteristics of two BEDT-TTF molecules in a dimer are almost the same. The interplanar distance between two BEDT-TTF molecules forming a dimer is 3.769Å 10 for λ-type salts and 3.45-3.53Åfor κ-type salts 18 , and the intradimer transfer integral of λ-(BEDT-TTF) 2 GaCl 4 is more than twice as large as the other transfer integrals 11,19 , suggesting that λ-type salts have a dimerized structure as in κ-type salts. The extended Huckel tight-binding band calculation showed the upper two and lower two bands with the large energy gap due to dimerization in λ-type salts, as shown in Fig.…”

Superconductivity in an Organic Insulator at Very High Magnetic Fields

“…These conducting layers alternate along the b-axis with layers containing linear chains of FeCl − 4 magnetic anions, hence the b-axis is the least conducting direction. Spin interactions between localized Fe 3+ 3d electrons and π conducting electrons are expected due to the short interatomic distance between the BETS molecules and the FeCl 4 anions.Single crystals of λ-(BETS) 2 FeCl 4 were obtained by electro-crystallization [7]. Annealed (low strain) gold wires (φ = 12.5 µm) were attached with graphite paint in a four-terminal arrangement along the c-axis.…”

“…Single crystals of λ-(BETS) 2 FeCl 4 were obtained by electro-crystallization [7]. Annealed (low strain) gold wires (φ = 12.5 µm) were attached with graphite paint in a four-terminal arrangement along the c-axis.…”