Cyanobenzene–Ethylenedithio–Tetrathiafulvalene Salts with ClO4–: Bilayer Polymorphs and Different Stoichiometries

The electrocrystallization from dichloromethane or tetrahydrofuran solutions of the dissymmetrical bis(ethylenedithio)-tetrathiafulvalene (ET) derivative cyanohenzene ethylenedithio tetrathiafulvalene (CNB-EDT-TTF) in the presence of perchlorate anion ClO4- affords two different polymorphs of salts with 4:1 stoichiometry, a previously described triclinic phase beta "(T)-(CNB-EDT-TTF)(4)ClO4 (1a), and a new monoclinic phase beta " M-(CNB-EDT-TTF)(4)ClO4, (1b), as well as a compound with 1:1 stoichiometry, (CNB-EDT-TTF)ClO4 (2), depending on the solvent and crystallization conditions:, The special conditions necessary for the growth of the untual 4:1 salts, requiring low 'current densities to oxidize the donors and subsequent slow diffusion,controlled association processes, are discussed. Both 4:1 -polyrriorphs present a bilayer structure of the donors induced by head-to-head C-N center dot center dot center dot H pairing interactions associated with a combination of R-2(2)(10) and R-4(2)(10) synthons between donors in nearby layers: These polymorphs share the same beta "-type donor packing pattern in the layers, but the anions which are disordered over two possible orientations in the triclinic phase appear ordered in the monoclinic one, with 4 doubling of the interlayer Cell axis, due to an alternation of the orientation of the molecules in the bilayers. The 1:1 salt 2 presents a crystal structure with dirgerized donors stacks. The donor molecules in nearby stacks are connected by a helical network of C-N center dot center dot center dot H pairing-interactions. A new polymorph of the neutral donor beta-CNB-EDT-TTF (3) is also described.