A variety of intermolecular interactions in tetracyanotetrafluoroquinodimethane (TCNQF4) charge transfer salts of fluorinated tetrathiafulvalenes

Abstract

The preparation and crystal structures of the 1:1 TCNQF₄ (tetracyanotetrafluoroquinodimethane) salts of two unsymmetrically substituted, fluorinated tetrathiafulvalenes, (2,2-difluorotrimethylenedithio)(ethylenedithio)tetrathiafulvalene (2) and (2,2-difluorotrimethylenedithio)tetrathiafulvalene (3) are described. A strong LUMO···LUMO overlap interaction leads to diamagnetic (TCNQF₄)₂²⁻ dimers in both salts. In (2)(TCNQF₄)·(Cl₂HCCH₂Cl), the 2^•+ radical cations also dimerise, giving rise to a layered, pseudo κ-type phase with alternating (2)₂²⁺ and (TCNQF₄)₂²⁻ and diamagnetic behaviour. On the other hand, in (3)(TCNQF₄) the cationic dimers adopt a weaker overlap and exhibit a magnetic singlet–triplet behaviour. The salt is also characterised by a complete fluorine segregation, the CF₂ groups of 3 facing the fluorine atoms of the TCNQF₄ moieties. In both salts the relative orientation of the cationic and anionic dimers is controlled by C–H···(N,F) hydrogen bonds (HB), demonstrating the activated HB donor character of the hydrogen atoms of the tetrathiafulvalenes upon oxidation together with the enhanced HB acceptor character of the nitrile groups of the TCNQF₄^•− radical anions.