Activation of C-HHalogen (Cl, Br, and I) Hydrogen Bonds at the Organic/Inorganic Interface in Fluorinated Tetrathiafulvalenes Salts
Résumé
The electrocrystallization of fluorinated bis(2,2-difluoropropylenedithio)tetrathiafulvalene (1) in the presence of linear (ICl2-, IBr2-, I2Br-) or cluster ([Mo6Cl14]2-) anions affords 1:1 and 2:1 cation radical salts such as [1][ICl2] and [1]2[Mo6Cl14](CH3CN)2. In both salts, the 1.+ radical ion adopts a boat conformation and envelops the anion through C-HHalanion (Halanion=Cl, Br, I) hydrogen bonds. This demonstrates the activating role of the neighboring electron-withdrawing CF2 moieties in the stabilization of bi- or trimolecular neutral entities. With smaller linear anions, fluorine segregation controls the solid-state associations of the bimolecular [1].+[X]- entities, and gives rise to layered materials with a limited overlap interaction between the open-shell organic cations and magnetic spin chain behavior. With the larger [Mo6Cl14]2- ions, a strong overlap interaction between radical cations gives rise to diamagnetic [1]22+ dimers, which alternate with the cluster anions to form hybrid organic/inorganic [1]22+[Mo6Cl14]2- chains. This behavior is also observed in [2]22+[Mo6Cl14]2-(CH2Cl2)2, in which compound 2 is the unsymmetrically substituted (ethylenedithio)(2,2-difluoropropylenedithio)tetrathiafulvalene. On the other hand, the unsymmetrically substituted 2,2-difluoropropylenedithiotetrathiafulvalene (3) affords a mixed-valence 4:1 salt with [Mo6Cl14]2-, which is formulated as [3]4[Mo6Cl14](CH3CN)2. This semiconducting salt is characterized by the coexistence of both the fluorine/fluorine segregation (with solvent inclusion) and the organic/inorganic segregation (with delocalized overlap interactions). Both Csp2-HCl and Csp3-HCl hydrogen bonds facilitate the stabilization of the organic/inorganic interface and the presence of conducting organic slabs.