Novel tellurium containing fulvalene-type electron donors, triselenatellurafulvalene (TSTeF) and diselenaditellurafulvalene (DSDTeF); synthesis, conductivities and crystal structures of their TCNQ complexes

Novel tellurium containing fulvalene-type electron donors, triselenatellura fulvalene (TSTeF) and diselenaditellurafulvalene (DSDTeF) are synthesized b y an efficient two- or three-stage procedure. They behave as superior elect ron donors to give highly conductive charge-transfer (CT) complexes with TC NQ. TSTeF-TCNQ shows a high conductivity of 2000 S cm(-1) at room temperatu re and is metallic down to 85 K, where a metal-insulator (MI) transition ta kes place. In contrast, the conductivity of DSDTeF-TCNQ is 1400 S cm(-1) at room temperature and monotonously increases down to 4.2 K without any MI t ransition. An X-ray structural analysis shows that TSTeF-TCNQ is crystallog raphically isostructural with TTF-TCNQ comprising typical one-dimensional d onor and acceptor columns. On the other hand, the crystal structure of DSDT eF-TCNQ is characterized by quasi one-dimensional donor stacks with side-by -side intercolumnar interactions through Te-Se contacts, which stabilize th e metallic state at low temperature.