Magnetic Coupling and Optical Properties of the S6-Dodecakis(trifluoromethyl)fullerene Radical Anions in the Layered Salt (PPN+)[C60(CF3)12.−]

• Published in: Chemistry : a European journal 2014-04, Vol.20 (18), p.5380-5387
• Main Authors: Konarev, Dmitri V., Romanova, Natalia A., Panin, Roman A., Goryunkov, Alexey A., Troyanov, Sergey I., Lyubovskaya, Rimma N.
• Format: Article
• Language: English
• Subjects: anions; Chemistry; Crystal structure; density functional calculations; fullerenes; magnetic properties; radical ions
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201304850

Poly(trifluoromethyl)fullerene S6‐C60(CF3)12 was reduced by sodium fluorenone ketyl in the presence of (PPN)Cl (PPN=bis(triphenylphosphine)iminium) to afford the salt (PPN)[C60(CF3)12] (1), which contains C60(CF3)12.− radical anions. In the crystal structure of 1, C60(CF3)12.− layers alternate with the PPN+ cations. There are short F⋅⋅⋅F contacts between C60(CF3)12.− radical anions within the layers but no C⋅⋅⋅C contacts. DFT calculations revealed that the negative charge on C60(CF3)12.− is distributed mainly between sp2 carbon and fluorine atoms, whereas spin density is localized mainly on the fullerene‐cage sp2 carbon atoms. IR and UV/Vis/NIR spectra in the solid state and solution showed characteristic changes relative to those of neutral S6‐C60(CF3)12 due to the formation of radical anions. The solid‐state electronic spectrum of 1 exhibits a single broad band at 738 nm attributed to C60(CF3)12.−. Crystals of 1 show a narrow EPR signal with g=2.0025 (ΔH=0.45 mT) at 300 K. The temperature dependence of the integral intensity follows the Curie–Weiss law with a negative Weiss temperature of −11.8 K (30–300 K) indicating antiferromagnetic interaction of spins. This dependence was approximated by the Heisenberg model for one‐dimensional chains of antiferromagnetically interacting spins with exchange interaction J/kB=−9.1 K. It was assumed that magnetic interaction between the C60(CF3)12.− spins in the layers is mediated by short F⋅⋅⋅F contacts. Anionic fullerenes: A salt of a multiply derivatized fullerene anion, namely, (PPN+)[C60(CF3)12.−] (1; PPN+=bis(triphenylphosphine)iminium), was obtained as single crystals (see figure; C gray, F green). The crystals of 1 exhibit a narrow EPR signal and rather strong antiferromagnetic coupling between the spins of the C60(CF3)12.− radical anions. It was assumed that this coupling is mediated by the network of short F⋅⋅⋅F contacts in the layers of radical anions.