The Tetrahydroxydicarbenium Cation (HO)(2)CC(OH)(2)(2+): Synthesis and Structure

摘要

abstract_textpOxalic acid forms in superacidic solutions HF/MF5 (M = As, Sb) its corresponding mono- and diprotonated salts HOOCC(OH)(2)MF6 and (HO)(2)CC(OH)(2)MF6(2) (M = As, Sb). The number of protonations is strongly dependent on the stoichiometric ratio of the Lewis acid with regard to oxalic acid. Mono- and diprotonated salts were characterized by vibrational spectroscopy and in the case of HOOCC(OH)(2)AsF6 (1) and (HO)(2)CC(OH)(2)SbF6(2) (4) by a single-crystal X-ray structure analysis. The salts crystallize in the monoclinic space groups P2(1)/c and P2(1)/n with eight, respectively four, formula units per unit cell. The vibrational spectra were compared to quantum chemical calculations of the cations HOOCC(OH)(2)(+) and (OH)(2)CC(OH)(2)(2+)center dot 4HF. In addition to this, an MEP analysis together with the NPA charges of (OH)(2)CC(OH)(2)(2+), (OH)(2)CC(OH)(2)(2+)center dot 6HF and oxalic acid were calculated to locate the positive charge. The protonation of oxalic acid does not lead to a remarkable change of the C-C bond length, which is discussed for the entire series of the oxalic skeleton, starting with the dianion and ending with the tetrahydroxy dication./p/abstract_text