Synthesis, Crystal Structure, and Electrical Properties of Novel Radical Cation Salts of Iodine‐Substituted TTF‐Derived Donors with the Nitroprusside Anion Exhibiting Strong ‐I ··· NC‐ Interactions

Radical‐cation salts of iodine‐substituted TTF derivatives [diiodoethylenedithiotetrathiafulvalene ( 1 ) diiodoethylenedithiodiselenadithiafulvalene ( 2 ), or iodoethylenedithiotetrathiafulvalene ( 3 )] with the [Fe(CN) 5 NO] 2− nitroprusside anion, namely, 1 4 ·[Fe(CN) 5 NO], 2 4 ·[Fe(CN) 5 NO] and 3 3 ·[Fe(CN) 5 NO], were synthesized by electrocrystallization from solutions of the appropriate TTF derivative in CH 2 Cl 2 with bis(tetraphenylphosphonium)nitroprusside [(PPh 4 ) 2 {Fe(CN) 5 NO}] as electrolyte. An X‐ray structure analysis indicates that the crystal structures of 1 4 ·[Fe(CN) 5 NO] and 2 4 ·[Fe(CN) 5 NO] are very similar. In both cases, molecules 1 and 2 are stacked along the c direction, with their long molecular axis parallel to each other. By contrast, in 3 3 ·[Fe(CN) 5 NO], molecules 3 are stacked in triad units in which two of the molecules are arranged in a face‐to‐face fashion and the remaining molecule is arranged in a head‐to‐tail fashion with respect to its neighboring molecules. In all cases, several effective iodine‐nitrogen contacts between donor molecules and [Fe(CN) 5 NO] 2− anions are observed. The room temperature electrical conductivities of 1 4 ·[Fe(CN) 5 NO], 2 4 ·[Fe(CN) 5 NO] and 3 3 ·[Fe(CN) 5 NO] are <10 −6 , 2.2 × 10 −2 and 5 S cm −1 , respectively. The temperature dependence of the electrical conductivity of 3 3 ·[Fe(CN) 5 NO] reveals semiconducting behavior with a small activation energy of 30 meV. The temperature dependence of the electrical conductivity of 2 4 ·[Fe(CN) 5 NO] also reveals a semiconducting behavior, but with two regimes: above 200 K the activation energy is 60 meV and becomes much smaller — 0.2 meV — below this temperature. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)