Solvent Dependent Structures of Melamine: Porous or Nonporous?

Two hydrogen-bonded organic frameworks (HOFs) of the melamine (MA), <b>MA-1-H<sub>2</sub>O</b> and <b>MA-2-DMF</b>, have been crystallized in H<sub>2</sub>O and DMF (<i>N</i>,<i>N</i>-Dimethylformamide), respectively. Structurally, <b>MA-1-H</b><sub><b>2</b></sub><b>O</b> and <b>MA-2-DMF</b> are condensed and porous, respectively. The porous <b>MA-2-DMF</b> sustains the porous feature under the solvent exchange by acetone, dichloromethane (CH<sub>2</sub>Cl<sub>2</sub>), and toluene, while it transforms into the condensed one under methanol (MeOH) and ethanol (EtOH). Furthermore, <b>MA-2-DMF</b> and <b>MA-2-Toluene</b> can undergo reversible single crystal–single crystal transformation with retention of the porous hydrogen-bonded organic frameworks.