Natalia A. Romanova

Synthesis and structures of trifluoromethyl derivatives of fullerenes C84(16) and C84(18)

Trifluoromethyl derivatives of fullerene C84 minor cage isomers Cs-C84(16) and C2v-C84(18) of general formulas C84(16)(CF3)2m (2m = 8, 10, 12, 14, 18) and C84(18)(CF3)2m (2m = 10, 12) were isolated by a multi-step HPLC from the products of high-temperature trifluoromethylation of a mixture of higher fullerenes. Molecular structures of these compounds were determined by single crystal X-ray diffraction using synchrotron radiation. The experimentally obtained structural data and the results of quantum chemical calculations were discussed in terms of general regularities of trifluoromethylation of C84 isomers in a wide range of compositions. The addition patterns of CF3 groups in C84(16/18)(CF3)2m molecules were found to depend on particular structural features of isomeric C84 cages.

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

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 sp(2) carbon and fluorine atoms, whereas spin density is localized mainly on the fullerene-cage sp(2) 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.

Formation of Doubly Charged Negative Ions under the Conditions of the Resonant Electron Capture by Fluorofullerenes

Doubly charged negative ions formed when electrons with controlled energies interact with isolated fluorinated fullerene molecules C60Fn (n = 36, 48) have been detected and investigated by resonant electron capture mass spectrometry. The dependence of the intensity of the formation of doubly charged negative ions of fluorofullerenes on the energy of attached electrons has been measured. An original method, which is based on the experimental data and does not require additional calibration quantities, has been developed for estimating the absolute cross section for the formation of doubly charged negative ions. The absolute cross sections for the formation of the most intensely formed ions C60F362− and C60F482− are estimated to be about 1.1 × 10−24 and 1.5 × 10−24 m2 at their maximum-yield energies of 2.0 and 1.6 eV, respectively.

Thermodynamic functions for the formation of isomeric CF3 adducts of C70 and C84

ABSTRACT Gas-phase formation enthalpies and Gibbs energies of formation (ΔfH°m; ΔfG°m) of trifluoromethylderivatives of fullerenes C70 and C84 are calculated at the DFT (density functional theory) level of theory. The approach employs homodesmic (HD) transtrifluoromethylation reactions and experimental thermochemical data on C60, C70, C84 and S6-C60(CF3)12.

On the energy dependence of the yield of doubly charged negative ions during the capture of free electrons by C60(CF3)12 trifluoromethylfullerene molecules

Peaks of C60(CF3)n2− doubly charged negative ions (n = 6–12) have been observed in the mass spectra of the resonance electron capture by trifluoromethylfullerene C60(CF3)12 molecules. It has been established that these ions are formed owing to the attachment of two free isoenergetic electrons. The autodetachment of an extra electron has been detected for the doubly charged molecular ions (n = 12). It has been established from the observation of the delayed fragmentation of the most abundant ions with n = 8 and 10 that the doubly charged negative ions, like their singly charged analogs, are metastable with respect to the separation of the CF3 fragment(s). The yield of doubly charged negative ions has been obtained as a function of the electron energy. By comparing them with the analogous dependences for the singly charged ions, the specific features have been revealed which were associated with the presence of the repulsive Coulomb barrier and the regular effect of the doubled energy of two additional electrons on the energy dependence of the dissociative decay of the doubly charged negative ions. The absolute cross section for the formation of the C60(CF3)102− ions has been measured. At the energy of their yield maximum near the 5 eV, it is ∼1 × 10−19 cm2.