Hyperfine adjustment of flexible pore-surface pockets enables smart recognition of gas size and quadrupole moment

The pore size and framework flexibility of hosts are of vital importance for molecular 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, quadrupole-moment 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.