Space Molecules\nin Superacidic MediaThe Synthesis\nand Structure of Monoprotonated Cyanoacetylene and Diprotonated Dicyanoacetylene

The molecules cyanoacetylene and dicyanoacetylene detected\nin the\natmosphere of Saturn’s largest moon Titan were investigated\nin superacidic media <i>X</i>F/<i>M</i>F<sub>5</sub> (<i>X</i> = H, D; <i>M</i> = As, Sb), <i>X</i>F/GeF<sub>4</sub>, and <i>X</i>F/BF<sub>3</sub>. Cyanoacetylene is obtained as a monoprotonated salt, while only\nthe diprotonated salt of dicyanoacetylene has been isolated. The salts\nwere characterized by vibrational spectroscopy, NMR spectroscopy,\nand single-crystal X-ray diffraction. The protonations lead to a significant\nshortening of the CN bond. The salts of [C<sub>3</sub>HXN][SbF<sub>6</sub>] (<i>X</i> = H, D) show very rare coupled oscillations\nin vibrational spectroscopy. The experimental results are discussed\ntogether with quantum chemical calculations at the M062X/aug-<i>cc</i>-pVTZ level of theory. The −<i>M</i> and\n−<i>I</i> effects of the CN moiety decrease\nby protonation of the nitrile moiety.