Yohji Misaki

Synthesis and properties of 1,3-dithiole-[3]- and [4]-dendralenes, acyclic systems of the corresponding [3]- and [4]-radialenes

Abstract 1,3-Dithiole-[3]- and [4]-dendralenes ( 2 and 3 ) have successfully been synthesized by using Vilsmeyer reactions on 2,2′-(ethanediylidene)bis(1,3-dithiole) ( 5 ) and 2 and the following Wittig reaction. Their electrochemical properties are discussed in comparison with those of 5 and 1,3-dithiole[4]radialene ( 4 ). Furthermore, conversion of 2 and 3 to 1,3-dithiole-[3]radialene and 4 , respectively, was attempted by using zero-valent nickel complexes.

Tetrathiapentalene-based organic conductors

Abstract The synthesis, structure and properties of tetrathiapentalene-based (TTP) organic conductors are reviewed. Among various TTP-type donors, bis-fused tetrathiafulvalene, 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (BDT-TTP) and its derivatives afford many metallic radical cation salts stable down to low temperatures, regardless of the size and shape of the counter anions. Most BDT-TTP conductors have a β-type donor arrangement with almost uniform stacks. Introduction of appropriate substituents results in molecular packing that differs from the β-type. A vinylogous TTP, 2-(1,3-dithiol-2-ylidene)-5-(2-ethanediylidene-1,3-dithiole)-1,3,4,6-tetrathiapentalene (DTEDT) has yielded an organic superconductor (DTEDT)3Au(CN)2 as well as metallic radical cation salts, regardless of the counter anions. (Thio)pyran analogs of TTP, namely (T)PDT-TTP and its derivatives produce molecular conductors with novel molecular arrangements. A TTP analog with reduced π-electron system 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene (BDA-TTP) has afforded several organic superconductors. Highly conducting molecular metals with unusual oxidation states (+1, +5/3 and neutral) have been developed on the basis of 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (BDT-TTP) derivatives and analogous metal derivatives M(dt)2 (M = Ni, Au).

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.

Bis(2-methylidene-1,3-dithiolo[4,5-d])tetrathiafulvalene (BDT-TTF): A tetrathiafulvalene condensed with 1,3-dithiol-2-ylidene moieties

Abstract Four alkyl derivatives of the title donor ( 1a–d ) have been synthesized. The electrochemical properties investigated by cyclic voltammetry and the electric conductivities of charge-transfer complexes with tetrafluoro-tetracyanoquinodimethane and 2,3-dichloro-5,6-dicyano-p-benzoquinone are also presented.

Dimeric and trimeric tetrathiafulvalenes with strong intramolecular interactions in the oxidized states.

New dimeric and trimeric TTF derivatives with methylenedithio spacers (1a,b, 2a, and 2b) have been synthesized. X-ray structure analysis revealed that TTF units of the dimer 1b adopted distorted face-to-face overlapping arrangement both in intra- and intermolecular stacking. Cyclic voltammetric study indicated that trimeric 2a was in favor of taking di- and tetracationic states, while the dimeric 1a was in favor of taking a monocation. The absorption spectroscopic study suggested an existence of the strong face-to-face interaction particularly in di-, tri-, and tetracationic state of the trimeric TTF derivatives.

A vinylogue of bis-fused tetrathiafulvalene: novel π-electron framework for two-dimensional organic metals

Several derivatives of 2-(1,3-dithiol-2-ylidene)-5-(2-ethanediylidene-1,3-dithiole)-1,3,4,6-tetrathiapentalene (1Aa), DTEDT, which is a vinylogue of bis-fused TTF (BDT–TTP) containing one 2,2′-ethanediylidenebis(1,3-dithiole)(2), have been synthesized. The cyclic voltammograms of the DTEDTs consist of four pairs of single-electron redox waves. Comparison of the first oxidation potentials (E1) reveals that donating ability of 1Aa is rather weaker than those of 2 and TTF, in spite of the extension of the apparent π-conjugation. Substituent effects on the E1 values suggest that the first oneelectron oxidation occurs mainly in the vinylogous TTF moiety. The smaller E2–E1 value of 1Aa compared with those of BDT–TTP, TTF and 2 suggests a decrease in the on-site coulombic repulsion in the dication. An X-ray structure analysis of the neutral 4,5-dimethyl-4′,5′-bis(methylthio) derivatives (1Be) reveals that the crystal has a so-called ‘κ-type array’ of molecules. An MNDO molecular orbital calculation indicates that the sulfur atoms at the termini of the vinylogous 1,3-dithiole rings are out of phase with the other sulfur atoms in the HOMO. The present donors have produced many molecular complexes exhibiting high conductivity. In particular, all of the radical-cation salts based on 1Aa obtained so far exhibit metallic conducting behaviour down to 1.4–4.2 K, regardless of the counter-anions.

New donors for organic metals

Abstract Six kinds of new donors ( 1 – 6 ), in which formally two or three sp 2 carbons are inserted between two 1,3-dichalcogenoles or four 1,3-dithiol-2-ylidene moieties are combined into cyclobutaneylidene framework, were synthesized. From comparison of the first oxidation potentials between the new donors and TTF, it was shown that the formers have superior donating ability to the latter. The new donors formed charge transfer salts with TCNQ ot TCNQF 4 , and the room temperature conductivities of the salts on compressed pellets were in the range of 0.03 – 0.8 S/cm. In particular, the 1 - TCNQ saltt was obtained as a single crystal, and the conductivity increased with decreasing temperature in the range of 300 (16 S/cm) and 200 K (23 S/cm).

A pentakis-fused tetrathiafulvalene system extended by cyclohexene-1,4-diylidenes: a new positive electrode material for rechargeable batteries utilizing ten electron redox

Pentakis-fused TTF derivatives extended with two cyclohexene-1,4-diylidenes (2a and 2b) have been successfully synthesized. Cyclic voltammetry of the tetrakis(2-ethylhexylthio) derivative (2b) has revealed that it exhibits five stages of the redox process to form 2b10+. A coin-type cell composed of a positive electrode incorporating the tetrakis(methylthio) derivative (2a) exhibits a discharge capacity of 196 mA h g−1, which corresponds to participation of a ten electron redox. It shows a high performance of energy density of 700 mW h g−1 and an output power density of 69 W g−1 with a relatively stable cycle-life performance (72% of the initial discharge capacity after 30 cycles).

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.

A Vinylog of Bis-Fused TTF: Novel π-Electron Framework for Metallic and Superconducting Organic Solids

Abstract The first vinylog of bis-fused tetrathiafulvalene (DTEDT) has been synthesized as a new donor component for organic conductors. Many cation radical salts of DTEDT showed metallic conducting behavior down to liquid helium temperature regardless of counter anions. Further, (DTEDT)3Au(CN)2 exhibited superconducting transition at 4 K under ambient pressure. X-Ray crystal structure analysis of (DTEDT)3Au(CN)2 reveals that this salt has a “uniform β-type” arrangement of donor molecules in the conducting sheet. The band calculation indicates it has a closed Fermi surface.