Negatively charged singly-bonded dimers of C-1-[C-70(CF3)(10)] and bare C-70 fullerene

摘要

Salts of fullerene derivative C-1-C-70(CF3)(10) and bare fullerene C-70 with cryptates of alkali metals as cations have been obtained: {cryptand[2.2.2](K+)}(2)[C-70(CF3)(10)(-)](2)center dot Solvent (1), {cryptand[2.2.2](K+)}(2)(C-70(-))(2 center dot)Solvent (2) and {cryptand[2.2.1](Na+)}(2)(C-70(-))(2)center dot 3C(6)H(4)Cl(2) (3) in the form of single crystals. Radical anions of both functionalized and bare fullerene C-70 form diamagnetic and EPR silent singly-bonded [C-70(CF3)(10)(-)](2) and (C-70(-))(2) dimers stable at least up to room temperature (according to the EPR data). The length of the intercage C-C bonds and the center-to-center interfullerene distances are 1.570(7) and 10.516 angstrom for the [C-70(CF3)(10)(-)](2) dimer in 1 and 1.576(4)-1.587(4) angstrom and 10.493-10.507 angstrom for the (C-70(-))(2) dimers in 2 and 3. Optical spectra of 1-3 manifest new bands in the NIR range characteristic of negatively charged fullerenes. These bands are blue shifted in the spectrum of 1 with [C-70(CF3)(10)(-)](2) in comparison with the spectrum of underivatized C-70(-). It is shown that negatively charged fullerene dimers show new low-energy broad absorption bands in the NIR range most probably associated with charge transfer between fullerene anions within the dimers. According to DFT calculations, the singly-bonded [C-70(CF3)(10)(-)](2) dimer demonstrates negative binding energy in the gas phase, but becomes bound by 54 kJ mol(-1) when the solvent effects are taken into account via the D-PCM model. Charge asymmetry incurred by CF3 groups at the pole region of anionic C-1-C-70(CF3)(10) promotes its dimerization in the condensed phase.