Tetrathiafulvalene-Diamide Salts with S···S and C···C Stacked Radical Couples

Three new radical salts, [DMT-TTF-(CONHMe)2]2CuBr4 (2), DMT-TTF-(CONHMe)2·ClO4 (3), and DMT-TTF-(CONHMe)2·Br (4), have been obtained by reacting DMT-TTF-(CONHMe)2 (1) with CuBr2 and Cu(ClO4)2 (DMT-TTF = dimethylthio-tetrathiafulvalene). The [DMT-TTF-(CONHMe)2]•+ cations of the three compounds are self-assembled to cation couples with short S···S and C···C stackings. Radical coupling was found within these TTF dimers, the intensity of which is related to the stacking distance between the coupled TTF molecules. When the S···S stacking is of a comparative intensity, the C···C stacking distance will play an important role in the antiferromagnetical coupling of the radicals. The intensity of the radical signals in electron spin resonance (ESR) was found to be in the order 2 < 3 < 4, which is related to the π···π stacking distance of the central CC bonds of the TTF moieties. The stronger the C···C interactions are, the weaker the radical signal becomes in the ESR spectra.