Highly Conducting and Superconducting Synthetic Metals

Research in the area of new synthetic metal (synmetal) superconductors continues to be stimulated by rapid developments in the chemistry and physics of these materials.1 Synmetals are unique in that they have metallic properties even though they contain no metals. However, this field remains very much materials limited because, as yet, it is not possible to predict which new materials will exhibit metallic properties. This situation is improving because structure-property correlations have been developed recently that may be used to predict likely candidates for superconductivity in the 4,4 j5,5 -tetramethyl-2,2 -bi-l-3-diselenolylidene, often called the tetra-methyltetraselenafulvalene (TMTSF) class of materials.2 

The synthesis of BEDT-TTF III was first reported in 1978 and was accomplished by phosphite coupling of the key thione intermediate, 1,3-dithiolo[4,5-b][l,4]dithiin-2-thione, commonly known as EDT-DTT 

Compound I may be prepared by the reduction of carbon disulfide either electrochemically6 or by use of an alkali metal.7 In this report we present the synthesis of BEDT-TTF, and derivatives, via the procedure just described beginning with the alkali metal reduction of carbon disulfide. In our hands we find this procedure easier to set up and use than that involving the electrolytic reduction of carbon disulfide. 

Submitted by PETER E. REED, JULIE M. BRAAM, LAUREN M. SOWA, ROBERT A. BARKHAU, GREGORY S. BLACKMAN, DAVID D. COX, GERALD A. BALL, HAU. H. WANG,f and JACK M. WILLIAMSf Checked by ALLEN E. UNDERHILL8 

Chemistry and Materials Science Divisions. Argonne National Laboratory, Argonne, IL. Correspondent, Chemistry and Materials Science Divisions, Argonne National Laboratory, Argonne, IL. 

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The search for new organic metals and superconductors has attracted a great deal of attention in synthetic chemistry and material science since the discovery of high electrical conductivity in conjugated polymers such as polyacetylene [1], Lots of theoretical studies have been carried out in order to understand the mechanism of conductivity and superconductivity in the conjugated polymers and related... 

Molecule-based materials exhibiting cooperative physical properties constitute one of the most active areas of interest in contemporary materials chemistry and science. An attractive chemical feature of these materials is the synthetic versatility provided by molecular chemistry. From the point of view of the physical properties, molecule-based materials can exhibit the properties of interest usually associated with the inorganic network solids, " as for example, high DC metal-like electrical conductivity and superconductivity, ferromagnetism, and non-linear optical responses. ... 

Polythiazyl (SN), . is an intrinsically metallic polymer. Fibrous highly crystalline samples are obtained by the solid-state polymerization of S2N2. The SN repeat unit has one excess electron and the polymer has a half-filled band. The density of states at Fp is low and (SN) is an anisotropic three-dimensional semimetal. Below 0.4 K, (SN) becomes superconducting both the transition-temperature and the room-temperature conductivity (2x 10 Scm ) are sample dependent. The conductivity of fibrous (SN) is enhanced to 2-4 x lO Scm" by exposure to halogens, which are assumed to form a layer on the surface of the fibres. Although efforts to prepare polymers related to (SN)j, have proved unsuccessful, new synthetic routes to SN) have yielded a better material. Despite the demonstration of efficient carrier-injection into semiconductors, the problems of preparation and manipulation have hindered the commercial use of (SN), ... 

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