ELECTRON-TRANSFER AND ION-PAIR FORMATION .34. SINGLE-CRYSTAL STRUCTURE OF THE SOLVENT-SEPARATED ION-PAIR [9,9'-BIANTHRYL-CENTER-DOT-CIRCLE-MINUS] [NA-CIRCLE-PLUS(DME)(3)]

The one-electron transfer to large pi-delocalized hydrocarbons provides an interesting possibility to crystallize solvent-separated ion-pair salts containing optimally solvated cations. Accordingly, the reduction of 9,9'-bianthryl in aprotic 1,2-dimethoxyethane (DME) solution at a sodium metal mirror allows to grow dark blue, brick-like crystals of its radical anion and threefold DME-solvated sodium cation. The structure of the radical anion is very similar to that recently published for the neutral molecule. According to AM1 enthalpy hypersurface calculations based on the structural data, the torsion angle between 60 degrees and 120 degrees is determined by the lattice packing and the negative charge is pi-delocalized predominantly within only one anthracene subunit. The counter cation [Na+(DME)(3)], reported only three times so far, shows a sixfold propeller-like coordination of approximate D-3 skeletal symmetry with contact distances Na+...O between 232 and 243 pm and angles measured angle ONa+O varying between 69 degrees and 159 degrees. Due to the small repulsion between the chelating DME molecules, the isodesmically calculated Na+ solvation enthalpy is more negative than that of the analogous tetrahydrofuran complex [Na+(THF)(6)] - as confirmed by the laboratory experience that salts of less stable anions are preferentially crystallized from a strongly cation solvating DME solution.