Spin-spin coupling between the two unpaired electrons in cross-conjugated tetrathiafulvalene dication radicals

Abstract

Spin-spin interactions were examined for bis(tetrathiafulvalenyl) (TTF) derivatives bridged with a 1,1-vinyl group (2,2-diphenyl, 1: 2,2-fluorenylidene, 2; and 2,2-dimethyl, 3). The chemical oxidation of these crossconjugated TTFs using AgClO 4 yielded characteristic seven-line ESR spectra, indicating the exchange interactions between the unpaired electrons on each TTF moiety. Compounds 2 and 3, in addition, exhibited fine structures and half-field resonances in the frozen solutions, which evidence the triplet interaction in the solid state, even with a twisted geometry of the molecular configuration. These findings substantiate the possibility of spin-spin interactions or triplet ground states predicted for some TTF oligomers.

Bi-TTF, Bis-TTF, and Related TTF Oligomers

“…Taking these results into consideration, we designed and synthesized the 1,1-bis(tetrathiafulvalenyl)ethylene derivatives 57a-e in order to examine the spin-spin interactions in their oxidation states. 42,75 The redox processes of 57a,b shown in Table 3 display no separation in either of the twoelectron transfers in their CVs, presumably due to the weak interaction between the two TTF moieties in these molecules. This weak interaction reflects the twisted structure, which was elucidated by X-ray analysis of 57a.…”

“…The calculations do predict the observed small singlet−triplet difference in 56 2+ compared with those in other bis-TTFs such as the 1,1-bis(tetrathiafulvalenyl)ethylene dication and the bis(tetrathiafulvalenyl)thioketone dication. Taking these results into consideration, we designed and synthesized the 1,1-bis(tetrathiafulvalenyl)ethylene derivatives 57a − e in order to examine the spin−spin interactions in their oxidation states. , The redox processes of 57a , b shown in Table display no separation in either of the two-electron transfers in their CVs, presumably due to the weak interaction between the two TTF moieties in these molecules. This weak interaction reflects the twisted structure, which was elucidated by X-ray analysis of 57a .…”

Bis(tetrathiafulvalenes) with aromatic bridges: electron delocalization in the oxidized species through EPR and theoretical studies

“…8 For bis(tetrathiafulvalenyl)ethylenes (TTF-[C sp 2]-TTF), a septet with a hyperfine constant of 6 G was also detected, but it was attributed to the dication with a strong spin exchange interaction. 38 This septet transforms into a quartet by decreasing the temperature just before solvent freezing or by recording the spectrum one day after the reaction. It was proposed that this modification was due to a molecular configurational change which reduces the spin-spin interaction.…”

Mono- and bis(tetrathiafulvaleno)hexadehydro[12]annulenesElectronic supplementary information (ESI) available: cyclic voltammograms of the annulenes 1 and 2. See http://www.rsc.org/suppdata/cc/b4/b407200f/

“…Tribenzohexadehydro[12]annulene 4 and its derivatives form sandwich complexes with silver salts both in solution and in the solid state. 6,8 Although silver salts are sometimes employed for complexation with sulfur atoms and for oxidation of TTF derivatives, 9 we expected that 1 and 2 might form sandwich complexes with silver salts because of their reduced oxidation potentials (Table 1). Thus, AgOCOCF 3 was used to form sandwich complexes 13 and 14 from 1 and 2 in CDCl 3 , whereas partial oxidation of 1 and 2 took place with AgClO 4 .…”