Variety of molecular conducting layers in the family of radical cation salts based on BEDT-TTF with the metal mononitrosyl complex [OsNOCl5]2−

Abstract

Four new BEDT-TTF radical cation salts with the [OsNOCl₅]²⁻ anion have been synthesized: α′-(BEDT-TTF)₄[OsNOCl₅]·C₆H₅NO₂ (1), δ-(BEDT-TTF)₄[OsNOCl₅]_1.33·(C₆H₅NO₂)_0.67 (2), κ-(BEDT-TTF)₄[OsNOCl₅]·C₆H₅CN (3) and β-(BEDT-TTF)₂[OsNOCl₅] (4). The salts were characterized by single-crystal X-ray diffraction, electrical resistance measurements, and electronic band-structure calculations. Evidence for commensurate structural modulations was found for 2 and 3. The crystals of 1, 3 and 4 are semiconductors while those of 2 exhibit a metal-to-insulator transition around 160 K. Analysis of the correlation between the crystal structure, transport properties and electronic structure of these and related salts suggests the possibility of smoothly changing the conductivity of κ-phases with two types of donors and dimers from semiconducting to metallic as well as the need to reconsider the origin of the metal-to-insulator transitions of δ-type salts.