Abstract
Hydrogen bonds' flexible distances and moderate strength entitle compounds to dynamic properties under external stimuli. Here we report multiple phase transitions and counter-intuitive CO(2) adsorption behavior of dynamic guanidinium sulfate (GS) salt assembled via hydrogen-bonds. Exploration based on the energy landscape generated by crystal structure prediction (CSP) reveals three porous GS phases with stability of α > β > γ and the inverse order of porosity, agreeing with experimental results. Transformations among polymorphs via heating or compressing involve ion rearrangement. Adsorption isotherms of β-GS indicate that CO(2) firstly enters the isolated cavities at a low gating pressure, and further increasing CO(2) pressure leads to the continuous gas uptake but reduced pressure at a critical point and thus an unexpected negative pressure inflexion (NPI), followed by the final adsorption saturation. Theoretical calculations demonstrate that the NPI behavior stemmed from the GS structural transition from β to more porous γ-phase, with the γ-GS phase becoming more energy-favorable as CO(2) uptake increases. Specific supramolecular interactions ensure CO(2) selectivity and easy regeneration. With a CO(2) uptake of 4.2 mmol g(-1) (273 K, 100 kPa), GS salt exhibits great promise for CO(2) capture and transport, demonstrating the potential of simple hydrogen-bonded salts as adaptive materials.