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, NiL ₂ (L=4-(4-pyridyl)-biphenyl-4-carboxylic acid), with diamondoid topology switches between non-porous (closed) and several porous (open) phases at specific CO ₂ and CH ₄ pressures. These phases are manifested by multi-step low-pressure isotherms for CO ₂ or a single-step high-pressure isotherm for CH ₄ . The potential methane working capacity of NiL ₂ approaches that of compressed natural gas but at much lower pressures. The guest-induced phase transitions of NiL ₂ 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 NiL ₂ . Specifically, the extended linker ligand, L, undergoes ligand contortion and interactions between interpenetrated networks or sorbate-sorbent interactions enable the observed switching.
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