Isolation and characterization of four isomers of a C(60) bisadduct with a TTF derivative. Study of their radical ions.

A family of triads composed of C(60) attached by a rigid spacer to two identical TTF moieties has been synthesized, and some of the isomers have been isolated and characterized by UV-vis spectroscopy, LDI-TOF-MS, and HMBC NMR spectroscopy. AM1 semiempirical calculations of the dipolar moments and the heats of formation of the different isomers have been carried out in order to verify their assignments. Oxidation and reduction of the triads affords the derived radical ion systems, TTF(+*)-C(60)-TTF(+*) and TTF-C(60)(-*)-TTF, which were studied by EPR spectroscopy. Spin density distributions of these radical cations and radical anions show that the unpaired electron is located mainly on the TTF and fullerene moieties, respectively. However, while the EPR signals obtained from the radical cations are very similar for all the isomers, the structured signals observed for the radical anions arising from the coupling of the unpaired electron with the hydrogen atoms of the methylene bridges in the spacer show that there is a strong influence of the isomerism on the spin distribution. Importantly, the theoretical calculations of the spin density distributions of the radical anions fit well with the experimental EPR results.