Metal-organic frameworks are a class of organic-inorganic hybrid and crystalline materials based on coordinatively bonded porous network. But the structure and function have been seldom investigated. The effective processing of MOF devices have always been hindered by the intrinsic feature of crystalline powders. The utilization of thermal rheology of glass material is expected to realize the effective preparation of grain-boundary-free and isotropic MOF glass membrane, which is one of the key goals of porous chemistry in the future. Different types of MOF glasses have been prepared by covering melt-quenching, mechanical or pressure treatment, bottom-up assembly in solution, ionic liquid-assisted melting and sequential perturbation. Nevertheless, the crystallization behavior of liquid and supercooled liquid greatly affects the processing and mechanical, optical, and electrical properties of glass materials, but the mechanism of microstructure evolution during the crystallization process is far from clear. It's even less clear on systematic study of the crystallization and high-temperature dynamic coordination chemistry for new MOF glass.

A highly porous and flexible MOF of [Co(L1)₂]_4n with 4-fold interpenetrated dia-net frameworks and another reference compound of Cu(L1)₂]_6n with 6-fold interpenetrated dia-net and dense frameworks, were synthesized by solvothermal reactions. The vapor treatment and subsequent thermal dehydration generated the h-CoL1 and dh-CoL1, respectively. The TG and DSC measurements were used to confirm the phase evolution from amorphous, through glass transition, to supercooled liquid, until either quenched glass or high-temperature re-crystallized phase. The in-suit and temperature dependent PXRD further confirmed the structure transformation process. X-ray total scattering atom pair distribution function spectra uncovered the short-middle-long range structure characters of both the glassy and re-crystallized MOFs. Infrared and Raman spectroscopy were used to analyze the coordination geometry changes among different states of MOF. The porosity of glassy g-CoL1 and recrystallized rec-CoL1 were investigated by using CO₂ adsorption-desorption curves at 195 K.

The [Co(L1)₂]_4n can turn into glassy state directly without high-temperature melting, facilitated by the multi-level synergistic perturbations of water coordination and subsequent thermal removal. As the first successful example of glass generated from traditional MOF based on sequential perturbation. TG and DSC revealed a glass transition at T_g = 560 K of the dehydrated and amorphous MOF, the subsequent formation of stable super-cooled liquid in the range of 558-586 K, the crystallization of the super-cooled liquid at T_c = 597 K, and the final decomposition above T_d = 695 K. Crystalline sample c-CoL1, glassy g-CoL1 obtained by quenching super-cooled liquid at different temperatures (563, 573, 583 K), and recrystallized rec-CoL1 at 593 K, at 195 K were tested CO₂ for isothermal adsorption. Based on structure match in the CCDC database and the synthesis of iso-reticular Cu-MOF, coupled with the Rietveld fitting analysis of PXRD spectrum, the structure of the recrystallized phase was verified to be a dense, 6-fold interpenetrated, and dia-net framework of [Co(L1)₂]_6n. Glass prepared by quenching MOF super-cooled liquids at different temperatures retained gas-accessible porosity and showed temperature-dependent variations, revealing the inherent structure difference in phase-homogeneous MOF super-cooled liquids.

The highly flexible, porous, and 4-fold interpenetrated dia-net frameworks of [Co(L1)₂]_4n can be perturbated by water molecule coordination and thermal dehydration to achieve structural disorder and direct glass transition without the need of traditional melting. The obtained MOF super-cooled liquid further transforms to a dense and six-fold interpenetrated dia-net MOF, through the coordinative self-assembly during high-temperature crystallization process. Gas accessible porosity of the quenched MOF glass was verified by gas sorption. Based on the relevance between the quenching temperature of super-cooled liquid and the corresponding porosity of the MOF glasses, the internal liquid structure difference of the homogeneous MOF super-cooled liquid is revealed. This study presents a vivid example of the multiphase structure evolution of MOF, covering different steps of crystalline, perturbated, super-cooled liquid, glass, re-crystallized states. This work thus reveals the unique high-temperature coordinative self-recognition and well-ordered self-assembly of MOF super-cooled liquid. Such new era of high-temperature dynamic chemistry also offers great opportunity for material processing and function loading of MOF based on the super-cooled liquid, glass and re-crystallized states of MOF.