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 F/F ( = H, D; = As, Sb), F/GeF, and F/BF. 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 [CHXN][SbF] ( = H, D) show very rare coupled oscillations in vibrational spectroscopy. The experimental results are discussed together with quantum chemical calculations at the M062X/aug--pVTZ level of theory. The - and - effects of the C≡N moiety decrease by protonation of the nitrile moiety.