Specific Isotope-Responsive Breathing Transition in Flexible Metal-Organic Frameworks.

Isotope-selective responsive system based on molecular recognition in porous materials has potential for the storage and purification of isotopic mixtures but is considered unachievable because of the almost identical physicochemical properties of the isotopes. Herein, a unique isotope-responsive breathing transition of the flexible metal-organic framework (MOF), MIL-53(Al), which can selectively recog-nize and respond to only D2 molecules through a secondary breathing transition, is reported. This novel phenomenon is examined using in-situ neutron diffraction experiments un-der same conditions for H2 and D2 sorption experiments. This work can guide the development of a novel isotope-selective recognizing system and provide opportunities to fabricate flexible MOF systems for energy-efficient purification of the isotopic mixture.