Mie Kodani

Synthesis and properties of novel heterocycle-fusedTTF-type electron donors: bis(propylenethio)tetrathiafulvalene (BPT-TTF),bis(propyleneseleno)tetrathiafulvalene (BPS-TTF), andtheir tetraselenafulvalene analogues (BPT-TSF and BPS-TSF)

A series of novel heterocycle-fused TTF-type electron donors, bis(propylenethio)tetrathiafulvalene (BPT-TTF, 5), bis(propyleneseleno)tetrathiafulvalene (BPS-TTF, 6), and their tetraselenafulvalene analogues (BPT-TSF, 7 and BPS-TSF, 8) have been effectively synthesized from a common starting compound, THP-protected pent-4-yn-1-ol. The solution electrochemistry reveals that all the new donors have good electron donating properties. Formation of their radical cation salts by electrocrystallization technique has been successfully achieved. All the radical salts derived from the TTF derivatives (5 and 6) are insulating owing to the complete charge transfer. On the other hand, the TSF derivatives (7 and 8) afford different types of highly conductive radical cation salts. Of these, 7·PF6, 7·AsF6 and 7·FeCl4 remain metallic down to liquid helium temperature.

Control of electronic states by bandwidth and band filling in organic conductors

In order to control the electronic states of organic conductors, two methods, (a)band filling and (b)bandwidth controls. have been applied. As for (a), it is the first time in organic conductors that the band filling in α-ET 3 (GaCl 4 ) -1 1-x (CoCl 4 ) -2 x (TCE) (x = 0.38, 0.43, 0.46, 0.64, 1.00) is controlled systematically. For (b). the bandwidth control has been carried out by chemical and physical methods in λ-D 2 GaCl 4 (D = ET, us-STF. BETS). By applying pressure, the system transfers from an antiferromagnetic insulator (λ-ET 2 GaCl 4 ). a metallic state down to 1.3 K (λ-(us-STF) 2 GaCl 4 under 18 kbar). to a superconductor (λ-BETS 2 GaCl 4 ). It is clarified that the λ-type organic superconductor has been obtained by the bandwidth control of the antiferromagnetic insulator.

Synthesis and properties of ethylenethiotetraselenafulvalene (ET-TSF) and its conductive radical cation salts

The title heterocycle-fused tetraselenafulvalene derivative, ET-TSF (ethylenethiotetraselenafulvalene) has been synthesized as a novel electron donor. Electrocrystallization of ET-TSF gave highly conductive radical cation salts with I 3 - , Cl - , Br - , and AuI 2 - counter anions. Among them, the AuI 2 salt isostructural with the organic superconductor (MDT-TSF)-AuI 2 (MDT-TSF = methylenedithiotetraselenafulvalene) was highly conductive (1600 S cm -1 ) and metallic down to 1.8 K with no superconducting transition.

Structures and Properties of Radical Cation Salts of Novel Tetraselenafulvalene Derivatives (BPT-TSF, EDT-PT-TSF, and BEST-TSF) with MX 4 (M = Fe, Ga, X = Cl, Br)-Type Anions

Using three different BETS variants (BPT-TSF 2 , EDT-PT-TSF 3 , and BEST-TSF 4 ), six new radical cation salts of D 2 MX 4 -type are prepared. The κ-type salts with FeCl 4 − anion obtained from the donors 2 and 3 are isostructural with the corresponding BETS salts. From the donor 3 , a radical salt with β-type donor packing is obtained with GaCl 4 − anion. All these salts from donors 2 and 3 are metallic down to low temperature. On the other hand, the donor 4 possessing selenium atoms in outer heterocycles gives two λ-type salts. They are highly conductive at room temperature, but not metallic at low temperature range.

Synthesis and properties of novel unsymmetrical tetraselenafulvalene donors, EDT-PT-TSF and EDT-PS-TSF

In order to develop novel electron donors, by structural modification to a superior electron donor, bis(ethylenedithio)-tetraselenafulvalene (BETS 2 ), unsymmetrical TSF derivatives ethylenedithio-propylenethio-TSF (EDT-PT-TSF 5 ) and ethylenedithio-propyleneseleno-TSF (EDT-PS-TSF 6 ) have been effectively synthesized. The synthetic method involves a one-pot formation of 1,3-diselenole-2-selones from acetylene derivatives, a cross-coupling to the TSF system, and finally a ring construction of the outer heterocycles. Electrocrystallization of 5 affords a series of conductive radical cation salts with BF 4 − , PF 6 − , AsF 6 − , ClO 4 − , and SbF 6 − anions, which are of the 2:1 or 3:2 composition ratio. All of the salts with 2:1 ratio are stable metals down to 4.2 K without any specific phase transitions. X-ray crystallographic analyses confirm that they have so-called κ-type donor arrangements.