Protonated oxalyl chloride and the ClCO cation.

The reactions of oxalyl chloride were investigated in the binary superacidic systems HF/SbF and DF/SbF. O-Monoprotonated oxalyl chloride was isolated and represents the first example of a protonated acyl chloride. Diprotonated oxalyl chloride is only stable in solution. Salts of the ClCO cation were synthesized from the reactions of oxalyl chloride or COClF with SbF in 1,1,1,2-tetrafluoroethane (R-134a, CFCFH). The colourless salts were characterized by low-temperature vibrational spectroscopy, NMR spectroscopy and single-crystal X-ray diffraction. (1,2-Dichloro-2-oxoethylidene)oxidanium hexafluoridoantimonate(V), [CO(OH)Cl][SbF], crystallizes in the monoclinic space group P2 and carbonyl chloride hexadecafluoridotriarsenate(V) [ClCO][SbF], in the trigonal space group P3, with two and three formula units per unit cell, respectively. Monoprotonated oxalyl chloride and the ClCO cation both display very short C-Cl bonds with a strong double-bond character.