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

Abstract

The crystal structure and thermal expansion behaviour of di­acet­y­lene were determined via diffraction methods and supplemented by spectroscopic techniques. The similarities to the structure of acetylene and implications for Titan in situ exploration are discussed.

Combining powder X-ray and neutron diffraction, the first crystallographic characterization of di­acet­y­lene (IUPAC designation 1,3-butadiyne) is presented and supplemented by Raman spectroscopy and periodic-DFT calculations. The structure is described in the space group Pnma, with a = 9.348 (2), b = 5.9890 (6), c = 5.6746 (11) Å and V = 317.69 (6) ų at 5 K, with four molecules in the unit cell resulting in a density of 1.0466 g cm⁻³. The di­acet­y­lene molecules are arranged in a layered structure dominated by C—H⋯π interactions, which leads to anisotropic thermal expansion behaviour. No structural phase transitions were observed across the 5–220 K tem­per­a­ture range at ambient pressure. The structural similarity with acetylene identifies it as a potential cocrystal component of particular importance for Titan’s surface chemistry in view of the upcoming NASA Dragonfly mission.