Polymorphism and Metallic Behavior in BEDT-TTF Radical Salts with Polycyano Anions

Up to five different crystalline radical salts have been prepared with the organic donor BEDT-TTF and three different polynitrile anions. With the polynitrile dianion tcpd 2− (=C[C(CN)2]3 2− ), two closely related radical salts: α'-(ET)4tcpd·THF (1) (THF = tetrahydrofurane) and α'-(ET)4tcpd·H2O (2) have been prepared, depending on the solvent used in the synthesis. With the mono-anion tcnoetOH − (=[(NC)2CC(OCH2CH2OH)C(CN)2] − ) two polymorphs with similar physical properties but different crystal packings have been synthesized: θ-(ET)2(tcnoetOH) (3) and β''-(ET)2(tcnoetOH) (4). Finally, with the mono-anion tcnoprOH − (=[(NC)2CC(OCH2CH2CH2OH)C(CN)2] − ) we have prepared a metallic radical salt: β''-(ET)2(tcnoprOH)(CH2Cl2CH3Cl)0.5 (5). Salts 1-4 are semiconductors with high room temperature conductivities and activation energies in the range 0.1–0.5 eV, whereas salt 5 is metallic down to 0.4 K although it does not show any superconducting transition above this temperature.