Polar Opposites Attract on Saturn’s Moon Titan

That polar and non-polar compounds do not spontaneously mix is a textbook rule of chemistry with few exceptions. Here we provide evidence for the intercalation of methane, ethane, and small hydrocarbons into the lattice structure of hydrogen cyanide (HCN), a highly polar molecule. Using cryogenic syntheses and Raman spectroscopy, we observe distinct shifts in vibrational modes in line with enhanced hydrogen bonding upon hydrocarbon insertion. Co-crystal structures composed of HCN and ethane that are both thermodynamically stable, and that closely match measured vibrational shifts are computationally predicted. Methane, ethane and HCN are major components of the atmosphere and surface of Saturn’s moon Titan, where they play key roles in shaping chemistry, weather, and landscape. Their intermixing may prove instrumental for explaining Titan’s chemical and geological evolution.