H. Sawa

Novel radical cation salts of organic π-donors containing iodine atom(s): the first application of strong intermolecular-I···X-(X = CN, halogen atom) interaction to molecular conductors

Abstract As a new architecture of crystal design in molecular conductors, an application of the intermolecular-I···X-(X = CN, halogen atom) interaction is presented. Novel radical cation salts of iodine-bonded tetrathiafulvalene (TTF) derivatives have been prepared and their unique crystal structures containing strong and directional cation-anion interactions are characterized.

Preparation and physical properties of an alloyed (DMe-DCNQI)2Cu with fully deuterated DMe-DCNQI (DMe-DCNQI = 2,5-dimethyl- N,N′-dicyanoquinonediimine)

Abstract Preparation, electrical resistivity, static magnetic susceptibility, and low-temperature X-ray study of the alloyed molecular conductor [(DMe-DCNQI-h 8 ) 1− x (DMe-DCNQI-d 8 ) x ] 2 Cu are described. The very low-pressure (P ca. 500 bar) region in the pressure-temperature phase diagram for (DMe-DCNQI) 2 Cu obtained by the helium gas pressure technique could be reproduced under ambient pressure by the alloying with DMe-DCNQI-d 8 . The results are discussed in terms of the strong correlation picture.

Magnetic Properties of Phenyl Nitronyl Nitroxides

Abstract Magnetic properties and crystal structures of several derivatives of phenyl nitronyl nitroxide (abbreviated as PNN; 2-phenyl-4,4,5,5-tetramethyl-4,5-dihydro-lH-imidazol-l-oxyl-3-N-oxide) are investigated. Some of them have the intermolecular interactions between the nitroxide group and the phenyl group, which are suggested to be favorable to ferromagnetic coupling. As a result of the coexistence of different types of magnetic interactions, anomalies in the temperature dependence of paramagnetic susceptibility are found for some compounds.

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.

Synthesis of DMe-DCNQI-d7 and deuterium-induced metal-insulator transition of (DMe-DCNQI-d7)2Cu

Abstract DMe-DCNQI-d 7 (DCNQI = dicyanoquiodiimine) was synthesized by applying 1 H/ 2 D exchange reaction, and its Cu and Li salts were prepared. An extremely sharp metal-insulator transition was brought about by deuteration, whereas (DMe-DCNQI-h 8 ) 2 Cu maintained its metallic state. A negligible isotope effect was observed on the resistivity behavior of the Li salt. The difference in reduction potential of the sole molecule in solution was found to be very small. Small but definite contraction of the stacking axis was caused by deuteration in both the Cu and Li salts. This ‘chemical pressure’ would be a plausible explanation of the drastic isotope effect observed in the Cu salt.

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.

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.

Metallic and superconducting salts based on an unsymmetrical π-donor dimethyl(ethylenedithio)tetraselenafulvalene (DMET-TSeF)

Abstract A series of radical cation salts (DMET-TSeF)2X (X = I3, AuI2, AuBr2, AuCl2, Au(CN)2) crystallize in the triclinic P 1 group. The DMET-TSeF molecules form zigzag columnar stacks. Short intermolecular chalcogen ⋯ chalcogen contacts are observed within and between stacks. The AuI2 salt exhibits a sample-dependent resistivity minimum around 25 K. The AuI2 salt without the resistivity minimum shows superconductivity with Tc = 0.58 K at ambient pressure. The AuBr2 salt exhibits a resistivity minimum around 35 K. Other salts remain metallic down to 4.2 K. These salts should be classified into a quasi one-dimensional system.

Anomalous pressure-temperature phase diagram of the molecular conductor, (DI-DCNQI)2Cu (DI-DCNQI=2,5-DIIODO-N,N′-dicyanoquinonediimine)

Abstract We report the temperature-dependent resistivity under pressure up to 22 kbar and the crystal and electronic band structures for the molecular conductor (DI-DCNQI) 2 Cu. In the (DCNQI) 2 Cu system, the application of pressure induces the metal-insulator (M-I) transition. (DI-DCNQI) 2 Cu shows the highest critical pressure (15.3 kbar). In contrast to previously reported (DCNQI) 2 Cu systems, however, this system turns into metallic state again above 20 kbar. This anomalous phenomenon is discussed in terms of an enhancement of the intercolumn LUMO…LUMO interaction.

Enhanced magnetic susceptibility of (DI-DCNQI)2Cu

Abstract The Cu salt of 2,5-diiodo-N,N′-dicyanoquinonediimine, (DI-DCNQI)2Cu, which is metallic down to 4 K, is found to exhibit enhanced and temperature dependent magnetic susceptibility, in contrast to other metallic DCNQI salts of Cu. The susceptibility shows a broad maximum around 110 K. The temperature dependence can be analyzed on the basis of a phenomenology using a characteristic temperature, T ∗ ≈ 200 K . This suggests an important role of spin fluctuations in a narrow 3d band near the Fermi level. To our knowledge, this is the first evidence for the effect of spin fluctuation in a molecular conductor based on π-d interactions.