Magnetic Coupling and Optical Properties of the S6‐Dodecakis(trifluoromethyl)fullerene Radical Anions in the Layered Salt (PPN+)[C60(CF3)12.−] |
| |
Authors: | Dr Dmitri V Konarev Dr Natalia A Romanova Roman A Panin Dr Alexey A Goryunkov Prof Sergey I Troyanov Prof Rimma N Lyubovskaya |
| |
Institution: | 1. Institute of Problems of Chemical Physics RAS, Chernogolovka, 142432 (Russia), Fax: (+7)?496‐522‐18‐52;2. Chemistry Department, Lomonosov Moscow State University, Leninskie Gory, Moscow, 119991 (Russia) |
| |
Abstract: | 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. |
| |
Keywords: | anions density functional calculations fullerenes magnetic properties radical ions |
|
|