R. Kato

Transport properties of ((CH3)4N) (Ni(dmit)2)2: A new organic superconductor

Abstract Transport properties of ((CH 3 ) 4 N) (Ni(dmit) 2 ) 2 crystals are studied in the temperature region from 300 to 1.5 K under hydrostatic pressure up to 15 kbar. A resistivity jump at around 100 K and a sharp rise of resistivity below 20 K are characteristic of this crystal. Hydrostatic pressure reduces both anomalies. In the sample where the low temperature anomaly was suppressed by high pressure, we have observed an onset of a superconducting transition under 3.2 kbar at 3.0 K. The transition temperature becomes high with increasing pressure. At 7 kbar, we find T c = 5.0 K .

Synthesis and properties of novel iodine-bonded π-donors containing selenium atoms, oxygen atoms or extended π-system

Abstract A new route for the syntheses of novel iodine-bonded unsymmetrical π-donors containing selenium atoms, oxygen atoms and extended π-system are reported. Especially on the syntheses of iodine-bonded EDT-TSeF derivatives, novel H 2 Se-free method has been developed.

Thermal and magnetic properties in organic metals (DMe-DCNQI)2Cu, (DMeO-DCNQI)2Cu and (DMe1-xMeBrx-DCNQI)2Cu: Enhancement of density of states

We have studied the electronic state in new type of organic conductors (DMe-DCNQI)2Cu, (DMeO-DCNQI)2Cu and (DMe1-xMcBrx-DCNQI)2 Cu (0<x<0.10), measuring the low temperature specific heat and magnetic susceptibility. For the sample of (DMe0.945MeBr0.055-DCNQI)2Cu, which reveals puzzling reentrant behavior in resistivity (metal- insulator- metal) with lowering temperature, an extraordinary enhancement of density of states at Fermi level is observed. Such remarkable properties of these Cu salts are discussed based on the mixed-valency of Cu atoms, which implies the mixing of 3d electrons of Cu into 2pπ conduction band of DCNQI through Cu-N coordination bond.

Magnetic properties and crystal structures of 2-hydro and 2-halo nitronyl nitroxide radical crystals

Abstract Magnetic properties and crystal structures of 2-hydro, 2-bromo and 2-iodo nitronyl nitroxide radicals (abbreviated as HNN, BrNN and INN, respectively), [HNN = 2-hydro-4,4,5,5,-tetramethyl 4,5-dihydro-1H-imidazol-1-oxyl 3-oxide], were investigated. These three radical crystals have similar structural units. In particular, BrNN and INN have almost the same molecular packings. However, only INN exhibits dominant ferromagnetic interactions.

Principal axis rotation of magnetoresistance in α-EDT-TTF[Ni(dmit)2] salt

Abstract The transverse magnetoresistance of α-EDT-TTF[Ni(dmit) 2 ] was investigated with the magnetic field rotated within a conducting ab-plane. It was found that the magnetic-field-orientation dependence of the magnetoresistance, δ R ( B )/ R (0) has the form P sin 2 (θ-δ)+ Q cos 2 (θ-δ), where θ is the angle between b-axis and magnetic field direction and ( P , Q , δ) are temperature dependent parameters. By examining the results based on the classical theory of magnetoresistance, it was concluded that the electrical conduction in this salt is made by both EDT-TTF and Ni(dmit) 2 above 20K, mainly by Ni(dmit) 2 below 10K.

Synthesis and physical properties of (DIETS)2[Au(CN)4]: A new θ-salt with a unique donor⋯anion network

A new θ-type salt, (DIETS) 2 [Au(CN) 4 ] (DIETS = diiodo(ethylenedithio)dithiadiselenafulvalene) has been prepared. A characteristic I…N intermolecular contact (d I … N = 3.018(7) A) exists in the crystal and forms a unique supramolecular donor…anion network. Although the calculated Fermi surface is a closed two-dimensional one, a sharp metal-insulator transition occurs at 226 K. The transition temperature is lowered under high pressure, which is in contrast to the pressure effect in the conventional θ-salts of BEDT-TTF (ET = bis (ethylenedithio)tetrathiafulvalene).

Crystal engineering in molecular conductors based on iodine-bonded π-donors

Abstract From the viewpoint of the “ crystal engineering ”, an application of the iodine-based cation···anion interactions is proposed as a new architecture of molecular conductors. Unique crystal structures and conducting properties are reviewed.

Selectively deuterated molecular conductor (DMe-DCNQI)2Cu —phase diagram and dimensionality—

Abstract The mixed-valence Cu salt of the π—acceptor DMe-DCNQI exhibits a unique pressure-temperature phase diagram. We present fine tuning of the effective pressure (0–500 bar) by selective deuteration of the DMe-DCNQI molecule. Especially, the selective deuteration at the methyl group(s) has made it possible to observe the giant metal-insulator-metal (reentrant) transition at ambient pressure. The 13 C-substitution at the cyano groups also positively shifts the effective pressure by ca 100 bar. In all these isotope effects, the coordination around the Cu ion is considered to play an important role. A simple tight-binding band calculation indicates that the hybridization between the organic pπ band and 3d orbital provides the three-dimensional Fermi surface, which well explains the result of the de-Haas van Alphen effect measurement.

Strange electric/magnetic behaviour of new (BEDT-TTF)(TCNQ)

Electric and magnetic properties for the third phase of (BEDT-TTF)(TCNQ) are investigated. The resistivity exhibits strange hysteresis in a wide range of temperature, with anomalies at 20 K, 80 K, and 175 K. The resistivity under pressure implies that the anomaly at 80 K originates from a kind of phase separation. The anomalies disappear when only 5 % of F1-TCNQ is doped. The magnetic susceptibility measured by SQUID showed apparent change at 20 K and 175 K, but no significant change was observed at 80 K. The spin susceptibility measured by ESR, on the other hand, exhibited gradual increase at the temperature from 80 K down to 20 K.

π-f Composite metals

Using the heavy rare-earth complex anions, [Ln(NCS) 6 ] 3- (Ln = Ho, Er, Yb and Y), we have synthesized three series of metallic compounds, (BO) x [Ln(NCS) 6 ], (TTP) x [Ln(NCS) 6 ] (x = 8) and (DIEDO) 6 [Ln(NCS) 6 ]. The BO and TTP salts are metallic down to very low temperature, while the resistivity of the DIEDO salts increases below about 40 K. These are the first examples of stable metals based on organic π-donors and rare-earth 4f ions.