Lower trifluoromethyl[70]fullerene derivatives: novel structural data and an survey of electronic properties

Abstract We revisit a series of trifluoromethylated C 70 (CF 3 ) n compounds with n  = 2–12 to provide a comprehensive comparative characterization thereof by means of a combination of physico-chemical methods. X-ray diffraction studies, including first structural determinations of the major isomers of C 70 (CF 3 ) 2 , C 70 (CF 3 ) 4 , and the third most abundant isomer of C 70 (CF 3 ) 8 as co-crystals with octaethylporphyrin Ni(II), produce accurate CF 3 group rotation angles and intergroup F⋯F distances that enable more reliable 19 F NMR signal assignment based on the through-space J FF spin-spin coupling relation to the F⋯F distances. Cyclic voltammetry measurements were performed in a potential range that covers oxidation on the one end and reduction to tri- or tetraanionic states on the other. It was demonstrated that the CF 3 addition patterns have marked effects on the redox potentials. A consistent set of the experimental HOMO energy values of the C 70 (CF 3 ) n molecules is reported for the first time in complement to the LUMO data, and the both sets of results were found to demonstrate good correlation with quantum-chemical DFT predictions. Most of the compounds exhibit electrochemically reversible one-electron reductions up to trianionic (sometimes even tetraanionic) state, a notable exception being C 70 (CF 3 ) 10 with irreversibility of its very first reduction. Bulk electrolysis of C 70 (CF 3 ) 12 at its 4-th reduction potential identifies CF 3 detachment as the most likely cause of the observed irreversible processes yielding C 70 (CF 3 ) 11 − anions as was identified by means of MALDI MS.