<p>Separation of CO₂ from gas mixtures is important in applications such as CH₄ gas purification and blue hydrogen production. Here we report selective CO₂ uptake by a family of flexible silver coordination polymers (AgCPs) that are ostensibly non-porous but exhibit latent porosity to CO₂ above a gate pressure, through a mechanism akin to dissolution in fluoroalkanes. The CO₂ sorption properties are rationally modified by changing the perfluoroalkyl chain length of the constituent perfluorocarboxylate ligands. The AgCPs do not take up CH₄ owing to failure of the dissolution mechanism, consistent with alkane–perfluoroalkane immiscibility. In situ single-crystal and powder X-ray diffraction enable direct visualization of the CO₂ molecule binding domains. These techniques also reveal associated structural changes in the AgCPs and confirm the gating mechanism of CO₂ uptake. The combination of perfluoroalkylcarboxylate ligands with the flexible silver(I) coordination sphere generates highly fluorinated but mobile regions of the crystals that play an integral role in the selective uptake of CO₂ over CH₄.</p><p></p>