A variety of intermolecular interactions in tetracyanotetrafluoroquinodimethane (TCNQF(4)) charge transfer salts of fluorinated tetrathiafulvalenes

The preparation and crystal structures of the 1:1 TCNQF(4) (tetracyanotetra fluoroquinodimethane) salts of two unsymmetrically substituted, fluorinated tetrathiafulvalenes, (2,2-difluorotrimethylenedithio)(ethylenedithio)tetra thiafulvalene (2) and (2,2-difluorotrimethylenedithio)tetrathiafulvalene (3 ) are described. A strong LUMO . . . LUMO overlap interaction leads to diam agnetic (TCNQF(4))(2)(2-) dimers in both salts. In (2)(TCNQF(4)). (Cl2HCCH2 Cl), the 2(.+) radical cations also dimerise, giving rise to a layered, pse udo kappa -type phase with alternating (2)(2)(2+) and (TCNQF(4))(2)(2-) and diamagnetic behaviour. On the other hand, in (3)(TCNQF(4)) the cationic di mers adopt a weaker overlap and exhibit a magnetic singlet-triplet behaviou r. The salt is also characterised by a complete fluorine segregation, the C F2 groups of 3 facing the fluorine atoms of the TCNQF(4) moieties. In both salts the relative orientation of the cationic and anionic dimers is contro lled by C-H . . . (N,F) hydrogen bonds (HB), demonstrating the activated HB donor character of the hydrogen atoms of the tetrathiafulvalenes upon oxid ation together with the enhanced HB acceptor character of the nitrile group s of the TCNQF(4)(.-) radical anions.