Investigations on a new series of organic conductors: The tetraselenotetracene iodides (TSeT-Ix)

A new series of radical-cation salts, the tetraselenotetracene iodides TSeT-Ix, have been synthesized by a cosublimation process. Three different stoichiometries have been obtained on which the structural and physical properties have been investigated. Phases B and C, TSeT-I0, 71 and TSeT-I0, 77, respectively, are semiconducting materials with incommensurate iodine sublattices; phase B exhibits a strong hysteresis effect detected by dc electrical conductivity and EPR linewidth measurements. The existence of elastic microdomains is postulated to explain this behavior. Concerning phase A, which is an ordered structure (TSeT-I0,5) we show that it is a molecular metal (the quality of which is sensitive to the preparation conditions). By using a general diagrammatic representation we are able to compare this salt to other one-chain compounds. We conclude that systems, the conductivity of which is dominated by radical cation chains, are organic metals potentially as good as charge transfer complexes belonging to TTF TCNQ series.