Takehiko Mori

New Organic Metals Based on Bis-Fused TTF Donors

Abstract A large number of radical-cation salts that retain metallic conductivity down to low temperatures have been prepared on the basis of bis-fused tetrathiafulvalene (TTF) donors. The stable states are associated with inherent tendency of these extended molecules to form two-dimensional conducting sheets. Structural and conducting properties of various TTP salts so far obtained are summarized.

THREE-COMPONENT ORGANIC CONDUCTORS ; (BEDT-TTF)2MM'(SCN)4

Abstract New organic conductors which contain a magnetic cation of Co2+ (d7, S=3/2), (BEDT-TTF)2MCo(SCN)4 [M=K, Rb, Cs], and related materials were prepared. The crystal structure analyses clarify that α-(BEDT-TTF)2MM′(SCN)4 [M=Rb, Cs, M′=Co, Zn] are isostructural and that these donor arrangements are α-type (strictly speaking θ-type). Although the band structure calculation affords the closed Fermi surface due to the large transverse overlap integrals, a metal-insulator (M-I) transition occurs at 20 K for α-(BEDT-TTF)2CsM′(SCN)4 [M′=Co, Zn] and at 190 K for α-(BEDT-TTF)2RbCo(SCN)4, respectively. The M-I transition temperatures of the former M=Cs salts are elevated by applying pressure. The magnetic susceptibilities of the M′=Co salts obey the Curie-Weiss law with θ=3–6K from 300 K to 20K. The relatively large θ might be originated from the superexchange of an anion network like… Co2+… NCS− as well as interaction through itinerant electrons in BEDT-TTF layer. Below 20 K the anomaly of χT was observed, whi...

Reflectance spectra of bis-fused TTF radical-cation salts

Abstract Polarized reflectance spectra were measured on bis-fused TTF radical-cation salts. The conductivity spectra of (TTM-TTP)I 3 exhibit an optical gap around 1000 cm −1 at room temperature, despite the metallic behavior in DC conductivity down to 160 K. The effective onsite Coulomb repulsion in the Hubbard model, U, is evaluated to be 0.5 eV, by use of the one-dimensional regular-stack model. The reflectance spectra of (TMET-TTP)(PF 6 ) 0.27 exhibit two-dimensional weak dispersions in the infrared region, being consistent with semiconductive behavior of this salt.

Transport properties of organic metal containing magnetic ions (BEDT-TTF)2CsCo(SCN)4

Abstract In order to investigate the nature of the 20 K metal-to-insulator transition of the title organic metal, (BEDT-TTF) 2 Cs Co(SCN) 4 (BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene), which involves localized spins on Co 2+ in the anion layers in addition to the itinerant electrons on the donor molecules, measurements of electrical resistivity under pressure, magnetoresistance, and thermoelectric power have been carried out. The pressure raises the metal-to-insulator transition temperature, but the transition is not affected by the magnetic field. The thermoelectric power does not show any clear anomaly near the transition. These observations suggest that the origin of the metal-to-insulator transition is related neither to the magnetic order of the localized spins on Co 2+ nor to simple SDW or CDW, but preferably related to the correlation of the donor electrons.

Crystal structures and conducting properties of TTM-TTP salts

Abstract Conducting properties of various cation radical salts of the title donor have been investigated. Among them (TTM-TTP)I 3 and β-(TTM-TTP) 2 I 3 show metallic conductivity down to T MI = 160 and 20 K, respectively. The results of X-ray crystal structure analysis of (TTM-TTP)I 3 and (TTM-TTP)(PF 6 ) 0.267 (THF) 0.6 are also presented.

Electronic Structures of Organic Conductors, (BEDT-TTF)2CsM(SCN)4 (M = Co, Zn)

Abstract 1H-NMR and EPR investigations of new organic conductors, (BEDT-TTF)2CsM(SCN)4(M=Co, Zn), have been performed. In the Co containing salt, the 1H-NMR spin-lattice relaxation rate, T 1 −1, is governed by the fluctuation of the localized magnetic moments on the Co2+ ions. The evaluated exchange interaction, J/κ B, is 0.09 K. A large increase in the 1H-NMR linewidth has been observed below 20 K for the Co salt, which can be explained as the effect of the static magnetization of the paramagnetic Co2+ ions. For the Zn containing salt, which has a closed d-shell, the 1H-NMR T 1 −1 and EPR properties exhibit anomalous behavior below 20 K, indicating a change in the electronic structure of the π-system around 20 K. The low-temperature electronic structure of the title compounds is discussed in the microscopic view.

Preparation, properties, and structures of planar anion complexes

Abstract Metal 1,1-, 1,2-dithiolates and 1,2-dioxylates based upon BEDT-TTF are prepared. (BEDT-TTF)[Ni(mnt)2] and (BEDT-TTF)2[Pd(i-mnt)2] have mixed columns and show semiconducting behaviors, whereas (BEDT-TTF)4[Pd(ox)2] with a segregated column and (BEDT-TTF)4[Pd(i-mnt)2] indicate metallic behaviors down to 160K and 180K, respectively.

Conductivity of Radical-Cation Salts of TTP Series Donors under High Pressure

Abstract Anomalous conducting behavior in TTP series salts, particularly (CPTM-TTP)4PF6, where CPTM-TTP is 2-(4,5-cyclopenteno-1,3-dithiol-2-ylidene)-5-(4,5-dimethylthio-1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene, has been investigated in detail. This charge-transfer salt shows resistivity jumps around 100K, but is still metallic at low temperatures. These jumps are suppressed under applied pressures. Below 30K several sudden drops of resistivity like superconducting transitions are observed, but are not affected by magnetic fields. This anomalous behavior is discussed in view of hysteretic transitions between two metallic phases.

Conducting properties of radical-cation salts of BEDT-TTP

Abstract Compressed pellets of BEDT-TTP chemically doped by such oxydizing reagents as I2 and Br2 have shown high conductivity. Electrochemically obtained EDT-TTP salts have also exhibited metallic conductivity.

Synthesis and properties of bis-fused ttf donors

Abstract A general synthetic method of bis-fused TTF (BDT-TTP) donors has been developed. The parent BDT-TTP has yielded many cation radical salts showing metallic conducting property down to low temperature (≤1.2 K). Crystal and electronic structures of (BDT-TTP) 2 SbF 6 are also presented.