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The physical properties of a series of organic superconductors with fourfold quasistacking structures, -BETS 2 GaX z Y 4Ϫz ͓BETSϭbis͑ethylenedithiotetraselenafulvalene; X,Y ϭF, Cl, Br; 0ϽzϽ2)] are changed continuously by tuning the value of z. The compound -BETS 2 GaBr z Cl 4Ϫz , has a superconducting ground state for 0ϽzϽz c ͑Ϸ0.8͒ and a semiconducting state for z c ϽzϽ2.0. The maximum T c is about 10 K, showing the existence of a 10-K class of non-ET organic superconductors ͓ETϭbis͑ethylenedithio͒tetrathiafulvalene͔. The temperature dependence of the resistivity closely resembles that for -type ET superconductors but the susceptibility behavior is different. The susceptibility of -BETS 2 GaBr 1.5 Cl 2.5 is isotropic and decreases fairly sharply below 30 K. No indication of a spin-flop transition was observed at 10 K, suggesting that the insulating phase that neighbors the superconducting phase is not antiferromagnetic at least down to 10 K.Since the discovery of the organic superconductor TMTSF 2 PF 6 , 1 a number of molecular superconductors have been developed by using planar molecules such as TMTSF, BEDT-ITF, 2 M (dmit) 2 , 3 etc. Bechgaard salts TMTSF 2 X (XϭPF 6 ,ClO 4 ,...͒ and -type BEDT-TTF ͑or ET͒ conductors are representative organic superconductors whose low-temperature properties have been intensively investigated. In spite of the large difference in the dimensionality of -metal bands, the phase diagrams of these two organic superconductors seem to share a common nature, that is, the superconducting phase neighbors in the antiferromagnetic insulating phase. In Bechgaard salts, the magnetic insulating ground state originates from the one dimensionality of the metallic band, whereas the strong electron correlation in twodimensional metal is considered to be responsible for the appearance of the magnetic phase of -type ET superconductors. At high pressure, the magnetic insulating states of TMTSF and ET systems are changed to superconducting states. A typical example of the phase diagram of organic conductors can be seen in the series of the isomorphous Bechgaard salts of TMTCF 2 X, ͓C͑chalcogen atom͒ϭS or Se͔. With increasing pressure, the ground state of TMTCF 2 X system tends to change in the following manner: spin-Peierls state→spin-density wave ͑SDW͒ state→superconducting state→metallic state. 4 The antiferromagnetic insulating phase was also found in the dmit superconductor, ␤-͓(CH 3 ͒ 4 N͔͓Pd(dmit) 2 ͔ 2 . 5,6 Contrary to a Bechgaard salt, this system is composed of the closed-shell cations and -acceptor molecules ͓Pd(dmit) 2 ]. ␤-͓(CH 3 ͒ 4 N͔͓Pd(dmit) 2 ͔ 2 exhibits a superconducting transition above 5 kbar (T c Ϸ6 K͒, 5 while NMR and ESR studies gave an evidence of the antiferromagnetic ground state at ambient pressure. 7 The dimeric molecular arrangement of ␤-͓(CH 3 ͒ 4 N͔͓Pd(dmit) 2 ͔ 2 resembles that of TMTCF 2 X and is quite different from the dimeric arrangement of the so-called -type ET superconductor. But the weakly semiconducting behavior of ␤-͓(CH 3 ͒ 4 N͔ ͓Pd(dmit) 2 ͔ 2 at ambient p...

We have synthesized novel trisulfide-bridged tetrathiafulvalene (TTF) dimer molecule in which two TTF moieties are connected to each other by two trisulfide chains. X-Ray crystal structure analysis reveals that the molecule has a unique cyclophane-like U-shape structure. The structure of the ClO 4 salt is also described.Research towards new donors for organic conductors based on the tetrathiafulvalene (TTF) framework has been actively pursued since the discovery of the metallic TTF-tetracyanoquinodimethane complex.1 Among them, the synthesis of tetrathiafulvalenophane was first reported in 1980 and extensively developed in the 1990s because of its unusual molecular structure and interesting intramolecular interaction.2,3 In particular several of these compounds have molecular structures like the dimeric structure of the coventional conducting salts such as the k-type bis(ethylenedithio)-TTF salts,4 which is related to the strong electron correlation system and Mott

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The first stable organic metals of the peri-ditellurium-bridged polyacene donor TMTTeN were obtained as TMTTeN2M(CN)2 (M = Ag, Au). Crystal structure analyses revealed three-dimensional networks through intermolecular Te···Te contacts. The salts are highly conductive (500−1000 S cm-1) and keep the metallic states down to low temperature. The extended Hückel tight-binding band calculation gave the quasi-three-dimensional Fermi surfaces.