Crystal structure of diacetylene unveiled by X-ray and neutron diffraction, Raman spectroscopy, and periodic-DFT

Combining powder X-ray and neutron diffraction, the first crystallographic characterisation of diacetylene (IUPAC designation 1,3-butadiyne) is presented and validated by Raman spectroscopy and periodic-DFT calculations. The structure is described in the space group P21/c with a = 6.14054 (17) ˚A, b = 5.7568 (8) ˚A, c = 9.3895 (10) ˚A, β = 89.886 (8)◦ and volume = 331.920(29) ˚A3 at 132 K, with four molecules within the unit cell resulting in a density of 1.0018 g cm−3. The diacetylene molecules and are arranged in a layered structure dominated by hydrogen-π interactions, which leads to an anisotropic thermal expansion behaviour. No structural phase transitions were observed across the temperature range of 5–220 K. The structural similarity with acetylene identifies it as a potential co-crystal component of particular importance for Titan’s surface chemistry in view of the upcoming NASA Dragonfly mission.