CO2-induced single-crystal to single-crystal transformations of an interpenetrated flexible MOF explained by in situ crystallographic analysis and molecular modeling

摘要

A molecular-level investigation is reported on breathing behaviour of a metal–organic framework ( 1 ) in response to CO _(2) gas pressure. High-pressure gas adsorption shows a pronounced step corresponding to a gate-opening phase transformation from a closed ( 1 _(cp) ) to a large-pore ( 1 _(lp) ) form. A plateau is observed upon desorption corresponding to narrow-pore intermediate form 1 _(np) which does not occur during adsorption. These events are corroborated by pressure-gradient differential scanning calorimetry and in situ single-crystal X-ray diffraction analysis under controlled CO _(2) gas pressure. Complete crystallographic characterisation facilitated a rationalisation of each phase transformation in the series 1 _(cp) → 1 _(lp) → 1 _(np) → 1 _(cp) during adsorption and subsequent desorption. Metropolis grand-canonical Monte Carlo simulations and DFT-PBE-D3 interaction energy calculations strongly underpin this first detailed structural investigation of an intermediate phase encountered upon desorption.