Protonated oxalyl chloride and the ClCO+ cation

The reactions of oxalyl chloride were investigated in the binary superacidic systems HF/SbF5 and DF/SbF5. 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 SbF5 in 1,1,1,2‐tetrafluoroethane (R‐134a, CF3CFH2). 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), [C2O(OH)Cl2][SbF6], crystallizes in the monoclinic space group P21 and carbonyl chloride hexadecafluoridotriarsenate(V) [ClCO][Sb3F16], in the trigonal space group P31, 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. The crystal structures of monoprotonated oxalyl chloride and the chlorocarbonyl cation are elucidated for the first time. Both display very short C—Cl bonds with a strong double‐bond character.