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, triselenatellurafulvalene (TSTeF) and diselenaditellurafulvalene (DSDTeF) are synthesized by an efficient two- or three-stage procedure. They behave as superior electron donors to give highly conductive charge-transfer (CT) complexes with TCNQ. TSTeFTCNQ shows a high conductivity of 2000 S cm^-1 at room temperature and is metallic down to 85 K, where a metal-insulator (MI) transition takes place. In contrast, the conductivity of DSDTeF-TCNQ is 1400 Scm^-1 at room temperature and monotonously increases down to 4.2 K without any MI transition. An X-ray structural analysis shows that TSTeF-TCNQ is crystallographically isostructural with TTF-TCNQ comprising typical one-dimensional donor and acceptor columns. On the other hand, the crystal structure of DSDTeF-TCNQ is characterized by quasi one-dimensional donor stacks with side-by-side intercolumnar interactions through Te-Se contacts, which stabilize the metallic state at low temperature.