Synthesis, electrical properties and crystal structure of a new radical-ion salt based on π-extended bis(TTF) and a Keggin heteropolymolybdate

Abstract

By electrocrystallization of 2,6-[4,5-bis(n-butylsulfanyl)-1,3-dithiol-2-ylidene]-4,8-bis(6-iodo-n-hexyloxy)-1,3,5,7-tetrathia-s-indacene (BHBDTI) and [NBu₄]₄[SiMo₁₂O₄₀] in the mixed solvent CHCl₂CH₂Cl and CH₃CN, the new radical-ion salt [C₄₂H₆₀Cl₂O₂S₁₂]₂[SiMo₁₂O₄₀] was prepared. It was characterized by means of IR and ESR spectroscopy and X-ray diffraction. In the crystal structure, organic radical dications and silicomolybdate anions are alternatively arranged along the a axis to form a 1-D conducting layer. The organic layer consists of two isolated groups of BHBDTI divided by the (011) plane without short interatomic contacts. However, in each group, BHBDTI molecules associate with each other in a head to tail manner running along the [011] direction and face-to-face overlapping with a relative shift by approximately one TTF subunit along the long axis of the molecule and a slight shift along the short axis of the molecule with significantly short S· · ·S contacts. The room-temperature d.c. conductivity determined by the two-probe method is 10^–4 S cm^–1, suggesting that the compound is a semiconductor.