Synthesis and theoretical characterization of an acetylene-ammonia cocrystal.

One of the smallest molecular cocrystals consisting of acetylene and ammonia is grown in situ on the X-ray diffractometer. The resulting 1:1 molecular cocrystal is composed of antiparallel layers of zigzag chains. Subunits of the crystal structure are already stable as small molecular aggregates as shown by ab initio calculations. These aggregates may be considered as infant stages of cocrystal formation.