A new ET-based radical salt, θ-(ET)(C₇H₇SO₃)·3H₂O (ET=bis(ethylenedithio)tetrathiafulvalene, C₇H₇SO₃^-=p-toluenesulfonate anion), has been synthesized by oxidative electrocrystallization.The crystal structure was determined by four-circle X-ray diffraction.The crystal belongs to triclinic system, P-1 space group with the unit cell parameters: a=0.8682(1) nm, b=1.2027(1) nm, c=2.5890(3) nm, α=87.025(6)°, β=89.117(8)°, γ=69.071(7)°, V=2.5216(5) nm³, R=0.0570.In the title crystal, the ET radicals are stacked to form columns along the a-axis and there is 49.30° dihedral angle between adjacent ET molecular planes.The inter-stack side-by-side S...S short contacts along the b-axis help to form a kind of cationic conducting sheet parallel to (001) plane.Layers of ET cations and layers of C₇H₇SO₃^- counter anions alternate to arrange along the c-direction.The H₂O molecules between the cationic sheet and the anionic sheet result in strong H-bond net which is beneficial to electrical conductivity.The room temperature conductivity at a certain direction on (001) plane of θ-(ET)(C₇H₇SO₃)·3H₂O crystal was measured to be 0.011 S·cm^-1.From 120 to 278 K, the resistivity-temperature curve demonstrates its semiconductor behavior, with an activation energy of 0.316 eV.However, with a metal-semiconductor phase transition around 276 K, it exhibits metallic conductivity from 278 to 286 K.

Key words: ET, synthesis, structure, conductivity