Efficient Gas Separation and Transport Mechanism in Rare Hemilabile Metal–Organic Framework

Understanding/visualizing
the established interactions between
gases and adsorbents is mandatory to implement better performance
materials in adsorption/separation processes. Here we report the unique
behavior of a rare example of a hemilabile chiral three-dimensional
metal–organic framework (MOF) with an unprecedented qtz-e-type
topology, with formula CuII2(S,S)-hismox·5H2O (1)
(hismox = bis­[(S)-histidine]­oxalyl diamide). 1 exhibits a continuous and reversible breathing behavior,
based on the hemilability of carboxylate groups from l-histidine.
In situ powder (PXRD) and single crystal X-ray diffraction (SCXRD)
using synchrotron radiation allowed us to unveil the crystal structures
of four different host–guest adsorbates (Ar@1, N2@1, CO2@1, and C3H6@1), rationalize the breathing motion, and unravel the mechanisms governing
the adsorption of these gases. Then this information was transferred
to implement efficient separations of mixtures of industrial and environmental
relevance, CO2/N2, CO2/CH4, and C3H8/C3H6, using 1 in packed columns as the stationary phase and dispersed
in a mixed matrix membrane.