Tatsuro Imakubo

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.

A supramolecular superconductor θ-(DIETS)2[Au(CN)4]

A supramolecular conductor θ-(DIETS)2[Au(CN)4] [DIETS = diiodo(ethylenedithio)diselenadithiafulvalene] has been revealed to be a new superconductor with Tc = 8.6 K (onset, 10 kbar) under uniaxial strain parallel to the crystallographic c-axis.

Supramolecular organic conductors based on diiodo-TTFs and spherical halide ion X−(X = Cl, Br)

Novel organic conductors based on four diiodotetrathiafulvalene derivatives, DIET (2-(4,5-diiodo-[1,3]dithiol-2-ylidene)-5,6-dihydro-[1,3]dithiolo[4,5-b][1,4]dithiine), DIETSe (2-(4,5-diiodo-[1,3]diselenol-2-ylidene)-5,6-dihydro-[1,3]diselenolo[4,5-b][1,4]dithiine), DIEDO (2-(4,5-diiodo-[1,3]dithiol-2-ylidene)-5,6-dihydro-[1,3]dithiolo[4,5-b][1,4]dioxine) and DIEDO-STF (2-(4,5-diiodo-[1,3]diselenol-2-ylidene)-5,6-dihydro-[1,3]dithiolo[4,5-b][1,4]dioxine) have been prepared using spherical halide ion X− (X = Cl, Br) as the counter anion. Crystal structure analyses have revealed that all halide salts contain supramolecular structures tailored by the strong I⋯X iodine bond and their molecular arrangement depends on the combination of the group 16 elements included in the donor molecule. The temperature dependence of the electrical resistivity of (DIET)2X(H2O)2 is metallic down to 4.2 K, and they have ideally two-dimensional Fermi surfaces within the donor layer. (DIETSe)2X(CH2Cl2) salts show small temperature dependence of the resistivity down to low temperatures and their “double column” structure is dominated by the Y-shaped architecture composed of the halide ion and the crystalline solvent. On the other hand, (DIEDO)2X and (DIEDO-STF)2X are semiconducting from room temperature. They have another type of “double column” structure, i.e. the adjacent donor molecules along the side-by-side direction are solid-crossing and two types of column are included in the donor layer. The packing motifs of the halide salts based on the oxygen-substituted donor molecules are the same but their electronic states are sensitive to changes in the chalcogen atoms on the inner TTF skeleton.

New organic conductors based on dibromo- and diiodo-TSeFs with magnetic and non-magnetic MX4 counter anions (M = Fe, Ga; X = Cl, Br)

Eight cation radical salts based on halogenated tetraselenafulvalene (TSeF) derivatives, dibromo(ethylenedithio)tetraselenafulvalene (DBrETSe) and diiodo(ethylenedithio)tetraselenafulvalene (DIETSe), were prepared using magnetic and non-magnetic MX4 counter anions (M = Fe, Ga; X = Cl, Br). Crystal structures of the DBrETSe salts depend on the halogen species on the MX4 counter anion. The MCl4 salts of DBrETSe are isostructural and crystallize in the orthorhombic space group Ibam and those of the MBr4 salts crystallize in the monoclinic space group C2/c. On the other hand, all four MX4 salts of DIETSe are isostructural and crystallize in the orthorhombic space group Ibam. In all eight crystals, donor molecules form a so-called β-type molecular arrangement and characteristic halogen bonds between the halogen atoms on the edge of the donor molecules and those of the counter anions are observed. (DBrETSe)2MX4 (M = Fe, Ga; X = Cl, Br) show stable metallic behaviour down to 4.2 K. This is in contrast to their iodinated analogues (DIETSe)2MCl4 (M = Fe, Ga), which show a metal–semiconductor transition at 11 K for the FeCl4 salt and at 12 K for the GaCl4 salt. No metal–semiconductor transition is observed for (DIETSe)2GaBr4, which contains the non-magnetic anion, but the transition is observed at 7.2 K for the corresponding FeBr4 salt, which contains a magnetic anion, indicating that the metal–semiconductor transition of (DIETSe)2FeBr4 correlates to the π–d electronic interaction through the I⋯Br halogen bonds. Antiferromagnetic orderings of d spins of the FeX4 anions are observed in (DBrETSe)2FeX4 and (DIETSe)2FeX4 (X = Cl, Br). In contrast to the low Neel temperature (TN ≈ 2.5 K) of the FeCl4 salts, the antiferromagnetic orderings occur at relatively high temperatures, i.e.TN = 7.5 K for (DBrETSe)2FeBr4 and TN = 7.0 K for (DIETSe)2FeBr4. Since the metallic state of (DBrETSe)2FeBr4 remains below TN, this salt is classified as a novel antiferromagnetic organic metal. On the other hand, the antiferromagnetic ordering of the d spins in (DIETSe)2FeBr4 takes place cooperatively with the metal–semiconductor transition around 7 K. These antiferromagnetic orderings of the d spins between the FeX4 anions cannot be explained by direct anion–anion interactions because of their long halogen⋯halogen distances between the FeX4 anions, and the importance of the π–d interaction between the donors and the counter anions through the halogen bonds is strongly suggested.

Novel molecular conductors, (DIETS)4M(CN)4(M = Ni, Pd, Pt): highly reticulated donor ⋯ anion contacts by –I ⋯ NC– interaction

The novel molecular conductors, (DIETS)4M(CN)4(M = Ni, Pd, Pt) where reticulated donor-anion contacts are constructed using the strong and directional –-I ⋯ NC– interaction, are synthesized and characterized.

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 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.

Hexagonal supramolecular organic conductors based on diiodo(pyrazino)tetraselenafulvalene: high yield recovery of the neutral π-donor by a simple chemical reaction

Conducting cation radical salts based on a pyrazine-fused iodine-bonded π-donor diiodo(pyrazino)tetraselenafulvalene (DIPSe) and octahedral anions AF6 (A = P, As, Sb) have been prepared by electrochemical oxidation. X-Ray structure analysis revealed that these three salts are isostructural and crystallize in the hexagonal P63/mcm space group. There is a strong and directional I⋯N iodine bond among the donor molecules, which is 18–19% shorter than the sum of the van der Waals radii. The hexagonal lattice is filled with the equilateral triangles of the donor molecules tailored by the I⋯N iodine bond and there are also two types of supramolecular channels including the counter anion and the crystalline solvent. The room temperature resistivities of these three salts are in the order of 10−2 Ω cm with metallic behaviour and they show a gentle upturn at around 250 K. In addition to the high-symmetrical crystal structure and the metallic conductivity, high yield recovery of the neutral π-donor from the cation radical salts has been accomplished by a simple chemical reaction. In situ1H-NMR monitoring of the reaction process indicates that the DIPSe cation radical was reduced by water and the characteristic supramolecular channels, which allow water molecules to access the cation radicals deep in the crystal, are essential for smooth progress of the recovery process.

Formation of two-dimensional weak localization in conducting Langmuir-Blodgett films

We report the magnetotransport properties up to 7 T in the organic highly conducting Langmuir-Blodgett(LB) films formed by a molecular association of the electroactive donor molecule bis(ethylendioxy)tetrathiafulvalene (BEDO-TTF) and stearic acid CH