Space Molecules in Superacidic MediaThe Synthesis and Structure of Monoprotonated Cyanoacetylene and Diprotonated Dicyanoacetylene

The molecules cyanoacetylene and dicyanoacetylene detected in the atmosphere of Saturn’s largest moon Titan were investigated in superacidic media XF/MF5 (X = H, D; M = As, Sb), XF/GeF4, and XF/BF3. Cyanoacetylene is obtained as a monoprotonated salt, while only the diprotonated salt of dicyanoacetylene has been isolated. The salts were characterized by vibrational spectroscopy, NMR spectroscopy, and single-crystal X-ray diffraction. The protonations lead to a significant shortening of the CN bond. The salts of [C3HXN]­[SbF6] (X = H, D) show very rare coupled oscillations in vibrational spectroscopy. The experimental results are discussed together with quantum chemical calculations at the M062X/aug-cc-pVTZ level of theory. The −M and −I effects of the CN moiety decrease by protonation of the nitrile moiety.