Bromide and Tribromide 4-Cyanobenzene-Ethylenedithio-Tetrathiafulvalene Radical Salts by Chemical and Electrochemical Routes

Abstract

Two salts of the dissymmetric TTF-derivative 4-cyanobenzene-ethylenedithio-tetrathiafulvalene (4-CNB-EDT-TTF) with bromide and tribromide anions and with different stoichiometries, namely, (1:1) (4-CNB-EDT-TTF)-Br 3 (1) and (4:1) (4-CNB-EDT-TTF) 4 Br (2), were obtained by electrocrystallization and diffusion methods, respectively. The crystal structures of these compounds, as determined by single-crystal X-ray diffraction, are based on head-to-tail donor dimers with ring over ring overlap and donor stack arrangement, interleaved by anions depending on the (1:1) or (4:1) salt, respectively. The 4:1 salt behaves as a Mott insulator. In both salts, the donors are connected to adjacent donors through C−N•••H−C interactions, which can be described as an modified R 2 4 (10)* synthon for 1 and a combination of R 2 2 (10) and R 2 4 (10) synthons for 2.

C–H⋯NC hydrogen bonding in cyanobenzene-ethylenedithio-tetrathiafulvalene compounds

“…1), and a large number of salts of this isomer with different anions were subsequently described. [24][25][26][27] The bilayer structure observed in 5-CNB-EDT-TTF (4 : 1) cation salts was never observed in the 4-CNB-EDT-TTF cation salts reported thus far, but C-H⋯NC interactions were always found to be present in a variety of different patterns. Therefore, the relative role of the weak hydrogen C-H⋯NC bonding, among the other intermolecular interactions, in the crystal packing of these compounds remains a relevant topic of discussion.…”

Bilayer Molecular Metal with a Polymeric Anion, β′′-(CNB-EDT-TTF)6 Ag∼7.95I∼9.19

“…6 The CN group position in the donor benzene ring, also plays a crucial role on the bilayer arrangement, as shown by several similar compounds based on the recently synthetized donor isomer 4-CNB-EDT-TTF without the bilayer arrangement. 7,8,9,10…”

“…In these salts, the partially oxidized donors are tightly packed and held head to head in bilayers, by a network of effective C–N···H–C interactions. − This unique bilayer arrangement has so far been restricted to salts with small discrete monoanions with linear, tetrahedral, or octahedral geometry, such as I 3 , ClO 4 , and PF 6 , and quite different structures are obtained with larger anions such as FeBr 4 , or complexes with square planar geometry . The CN group position in the donor benzene ring also plays a crucial role in the bilayer arrangement, as shown by several similar compounds based on the recently synthesized donor isomer 4-CNB-EDT-TTF without the bilayer arrangement. − …”