Structural diversity in charge transfer salts based on Mo3S7 and Mo3S4Se3 clusters complexes and bis(ethylenedithio)tetrathiafulvalene (ET)

Abstract

Chemical modification of the trinuclear [Mo₃(μ₃-S)(μ₂-S₂)₃Br₆]²⁻ cluster, at either the outer bromine or the disulfide ligands, allows the facile preparation of the dianions [Mo₃(μ₃-S)(μ₂-S₂)₃(tdas)₃]²⁻ ([1]²⁻) (tdas = 1,2,5-thiadiazole-3,4-dithiol), [Mo₃(μ₃-S)(μ₂-SSe)₃Br₆]²⁻ ([2]²⁻) and [Mo₃(μ₃-S)(μ₂-S₂)₃Cl₆]²⁻ ([3]²⁻). Electrocrystallization of bis(ethylenedithio)tetrathiafulvalene (ET) in the presence of these dianions affords a series of charge transfer salts, namely (ET_A)(ET_B)[1], (ET_A)(n-Bu₄N)[2], (ET_A)(ET_B)[3]₂·CH₃CN, and ((ET_A)(ET_B)(ET_C)(ET_D))₂{[3]₂Cl}·CH₃CN, where the ET subscripts denote crystallographically independent molecules. In all cases, the various cluster–cluster, cluster–donor and donor–donor interactions give rise to rich structural diversity in the inorganic and organic sublattices. Raman spectroscopy has been used to account for the degree of charge transfer in the organic donor ET. The ET molecules are oxidized to the integral 1+ oxidation state in compounds (ET_A)(ET_B)[1] and (ET)(n-Bu₄N)[2] and to the integral value of 2+ in compound (ET_A)(ET_B)[3]₂·CH₃CN. Their transport properties reveal semiconducting behaviour with a room temperature conductivity of 4 × 10⁻⁵ S· cm⁻¹ and an activation energy of 280 meV for compound (ET_A)(ET_B)[1] while the other two compounds are insulators. Non-integer values less than 1+ are observed for ((ET_A)(ET_B)(ET_C)(ET_D))₂{[3]₂Cl}·CH₃CN which shows metallic behavior at high temperatures with an irreversible transition to an activated conductivity at ca. 270 K.