Crystal melting and vitrification behaviors of a three-dimensional nitrile-based metal-organic framework

A three-dimensional (3D) metal-organic framework [Ag(pL2)(CF₃SO₃)]·2C₆H₆ (pL2 = 1,3,5-tris(4-cyanophenylethynyl)benzene), composed of Ag⁺ and tripodal nitrile ligands, was prepared to enable the investigation of its crystal melting and vitrification behaviors. The guest-free state showed a crystal melting at 271 °C, and the liquid state transformed into a glassy state via cooling. The vitrification of the crystalline compound into an amorphous glassy state was also obtained by mechanical hand-grinding. The structure of the glassy state retained the 3D networked structure, confirmed by FT-IR, X-ray absorption, and scattering measurements. The mechanically induced glass showed a small uptake of CO₂ and a strong affinity for benzene and H₂O vapors, confirmed by gas sorption isotherms. Powder X-ray diffraction studies have revealed that the vitrified structure returned to the original 3D crystalline structure by exposure to these vapors.