SINGLE-CRYSTAL STRUCTURE OF THE SOLVENT-SEPARATED RADICAL-ION PAIR [9,10-DIPHENYLANTHRACENE(CENTER-DOT)CIRCLE-MINUS][NA-CIRCLE-PLUS(THF)(6)] AND ITS IMPLICATION FOR CATION SOLVATION

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 9,10-diphenylanthracene in aprotic THF solution at a sodium metal mirror allows to grow dark-blue prismatic crystals of its radical anion and sixfold THF-solvated sodium cation. The structure of the radical anion is very similar to that recently published for the neutral molecule. According to AMI hypersurface calculations based on the structural data, the phenyl twist angles obviously must be determined by lattice packing, and the negative charge is delocalized predominantly within the anthracene pi system. The counter cation [Na+(THF)(6)], reported ordered for the first time, shows nearly octahedral coordination within a rather densily packed solvent shelf. Due to the strong repulsions between the solvent molecules, its isodesmically calculated solvation enthalpy is smaller than that of the analogous dimethoxyethane complex [Na+(DME)(3)].