Multiple Structural and Phase Transformations of MOF and Selective Hydrocarbon Gas Separation in its Amorphous, Glass Phase States

Abstract

The first wide-view image of multiple structural and phase transformations for MOFs, ranging from crystal state transformations to the extreme limit approaching liquid/glass phase, was presented. The process involves i) an initial crystalline transformation from square-layer framework [Co₂(pybz)₂(CH₃COO)₂] ⋅ DMF (Co2) to a 3-fold interpenetrated and ordered vacancies contained framework [Co(pybz)₂(CH₃OH)₂] ⋅ 2CH₃OH (CoM) due to in situ disassemble-reassemble, ii) thermal induced departure of a pair of cis-form coordinated methanol in CoM leads to amorphous framework a-dCoM, iii) glass transition to super-cooled liquid scl-dCoM, iv) obtaining MOF glass g-dCoM upon quenching the super-cooled liquid, and v) re-crystallization of super-cooled liquid generates 6-fold interpenetrated dia-net framework [Co(pybz)₂]_6n (rec-dCoM) under further heating. The access to glass from CoM, provides a new self-perturbation strategy to create MOF glasses without melting. The wider pore size distribution in amorphous/glassy MOFs than crystalline precursor achieved the first time selective hydrocarbon gas separation by breakthrough experiments, which bring efficient separation of 1 : 99 C₂H₂/C₂H₄ by either a-dCoM or g-dCoM and produce polymer grade C₂H₄ with purity≥99.5 % after a single adsorption process. Furthermore, the mixture of 50 : 50 C₃H₆/C₃H₈ can be separated by a-dCoM.