STRUCTURE AND PHYSICAL-PROPERTIES OF (EP-TTP)(2)AU(CN)(2)

A new series of organic donors, bis-fused tetrathiafulvalenes (TTF), have afforded a number of highly conducting radical-cation salts that maintain metallic conductivity down to liquid helium temperatures.(1)) The main obstacle to preparing salts of these donors is, however, poor solubility of these donors in organic solvents; this makes the conventional electrochemical crystal growth difficult. In particular, ''capped'' moieties such as ethylenedithio group considerably diminish the solubility. Unsymmetrical substitution, however, considerably improve the solubility. For example, 2-(4,5-ethylenedithio-1,3-dithiol-2-ylidene)-5-(4,5- trimethylenedithio-1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (hereafter abbreviated symbolically as EP-TTP, Scheme 1) shows a little better solubility than its symmetrical analogs. Because fairly good crystals of its [Au(CN)(2)](-) salt was obtained and showed metallic conductivity down to low temperatures, the present paper describes the results of its single-crystal structure analysis, energy-band calculation, electrical conductivity, thermoelectric power, and ESR measurements.