Structural, electrical and magnetic properties of low-dimensional conductors based on unsymmetrical pi donor EDT-TTF and analogous selenium-substituted molecules

Organic conductors based on the unsymmetrical pi donor molecule EDT-TTF (et hylenedithiotetrathiafulvalene) or its selenium-substituted analogs (EDST, EDTS) and tetrahedral anions GaCl4- were prepared. The crystal structure de terminations and the extended Huckel tight-binding band calculations indica te these systems to be quasi-one-dimensional conductors similar to TMTTF or TMTSF systems (TM systems). Electrical resistivity and magnetic susceptibi lity measurements and low-temperature X-ray diffraction experiments suggest ed a spin-Peierls ground state for (EDT-TTF)(2)GaCl4. (EDST)(2)GaCl4 and (E DTS)(2)GaCl4 exhibit metallic behavior down to ca. 40 K. The electric and m agnetic properties of (EDST)(2)GaCl4 suggested a semimetallic state at low temperature. In spite of the similarity in the crystal and electronic band structures between TM and EDT systems, these two series of quasi-one-dimens ional conductors do not share the same 'generalized phase diagram'. The ele ctron-lattice interaction seems to be important in EDT conductors. The elec tric and magnetic properties of the isostructural systems with magnetic FeC l4- anions were also examined. The magnetic interaction between the high-sp in Fe3+ ions was found to be very weak.