Drastic Rearrangement of Self-Assembled Hydrogen-Bonded Tapes in a Molecular Crystal

For the first time, a two-step single-crystal-to-single-crystal (SCSC) transformation at varying temperatures is reported for a 2:1 hydrogen-bonded (H-bonded) crystal of 2-pyrrolidone (Py) and chloranilic acid (CA). Crystallographic studies revealed that sheets composed of H-bonded tapes exhibited a drastic translation of approximately 7 Å in the first SCSC transition, which was triggered by the freezing of the out-of-plane thermal motion of Py. The second SCSC transition was primarily caused by competing intersheet interactions between CA···CA and Py···Py, which resulted in a sheet translation of approximately 2 Å. Anisotropic and collective translations, which were accompanied by morphological changes in the crystal, were attributed to the selective and directional characteristics of H-bonds.