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

By electrocrystallization of 2,6-[4,5-bis(n-butylsulfanyl)-1,3-dithiol-2-yl idene]-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 ra dical-ion salt [C42H60Cl2O2S12](2)[SiMo12O40] was prepared. It was characte rized by means of IR and ESR spectroscopy and X-ray diffraction. In the cry stal structure, organic radical dications and silicomolybdate anions are al ternatively arranged along the a axis to form a 1-D conducting layer. The o rganic layer consists of two isolated groups of BHBDTI divided by the (011) plane without short interatomic contacts. However, in each group, BHBDTI m olecules associate with each other in a head to tail manner running along t he [011] direction and face-to-face overlapping with a relative shift by ap proximately one TTF subunit along the long axis of the molecule and a sligh t shift along the short axis of the molecule with significantly short S ... S contacts. The room-temperature d.c. conductivity determined by the two-p robe method is 10(-4) S cm(-1), suggesting that the compound is a semicondu ctor.