Reversible Switching between Highly Porous and Nonporous Phases of an Interpenetrated Diamondoid Coordination Network That Exhibits Gate-Opening at Methane Storage Pressures.

Herein, we report that a new flexible coordination network, NiL2 (L=4-(4-pyridyl)-biphenyl-4-carboxylic acid), with diamondoid topology switches between non-porous (closed) and several porous (open) phases at specific CO2 and CH4 pressures. These phases are manifested by multi-step low-pressure isotherms for CO2 or a single-step high-pressure isotherm for CH4 . The potential methane working capacity of NiL2 approaches that of compressed natural gas but at much lower pressures. The guest-induced phase transitions of NiL2 were studied by single-crystal XRD, in situ variable pressure powder XRD, synchrotron powder XRD, pressure-gradient differential scanning calorimetry (P-DSC), and molecular modeling. The detailed structural information provides insight into the extreme flexibility of NiL2 . Specifically, the extended linker ligand, L, undergoes ligand contortion and interactions between interpenetrated networks or sorbate-sorbent interactions enable the observed switching.