Hyperfine adjustment of flexible pore-surface pockets enables smart recognition of gas size and quadrupole moment† †Electronic supplementary information (ESI) available: Experimental section, PXRD patterns, crystallographic tables and characterization details. CCDC 1561837–1561845. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc03067c Click here for additional data file. Click here for additional data file.

The pore size and framework flexibility of hosts are of vital importance formolecular recognition and related applications, but accurate control of these parameters is very challenging. We use the slight difference of metal ion size to achieve continuous hundredth-nanometer pore-size adjustments and drastic flexibility modulations in an ultramicroporous metal–organic framework, giving controllable N2 adsorption isotherm steps, unprecedented/reversed loading-dependence of H2 adsorption enthalpy, quadrupolemoment sieving of C2H2/CO2, and an exceptionally high working capacity for C2H2 storage under practical conditions (98 times that of an empty cylinder). In situ single-crystal X-ray diffraction measurements and multilevel computational simulations revealed the importance of pore-surface pockets, which utilize their size and electrostatic potential to smartly recognize the molecular sizes and quadruple moments of gas molecules to control their accessibility to the strongest adsorption sites.