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

Abstract

Organic conductors based on the unsymmetrical π donor molecule EDT-TTF (ethylenedithiotetrathiafulvalene) or its selenium-substituted analogs (EDST, EDTS) and tetrahedral anions GaCl ₄ ^– were prepared. The crystal structure determinations and the extended Hückel tight-binding band calculations indicate these systems to be quasi-one-dimensional conductors similar to TMTTF or TMTSF systems (TM systems). Electrical resistivity and magnetic susceptibility measurements and low-temperature X-ray diffraction experiments suggested a spin-Peierls ground state for (EDT-TTF) ₂ GaCl ₄ . (EDST) ₂ GaCl ₄ and (EDTS) ₂ GaCl ₄ exhibit metallic behavior down to ca. 40 K. The electric and magnetic properties of (EDST) ₂ GaCl ₄ 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-dimensional conductors do not share the same ‘generalized phase diagram’. The electron–lattice interaction seems to be important in EDT conductors. The electric and magnetic properties of the isostructural systems with magnetic FeCl ₄ ^– anions were also examined. The magnetic interaction between the high-spin Fe ³⁺ ions was found to be very weak.