A novel ultramicroporous coordination polymer, namely [Cu(F-pymo)₂(H₂O)_1.25]_n (1, F-pymo = 5-fluoropyrimidin-2-olate), has been prepared and structurally characterized. 1 displays a zeolitic gismondine (GIS) topology, with ca. 2.9 Å wide helical channels which, in the thermally activated counterpart (1‘), account for a 13% void volume and are responsible for the observed selective solid−gas adsorption properties toward H₂, N₂, and CO₂. At 77 K 1‘ behaves as a molecular sieve, selectively adsorbing H₂ over N₂, possibly due to size-exclusion reasons. At variance, although CO₂ molecules are slightly larger than the pore size, they are readily incorporated by 1‘ at temperatures as high as 433 K. Variable-temperature X-ray powder diffraction (TXRPD) studies, in the temperature range 303−473 K, show that dehydration is reversible and has almost negligible effects on the network. At variance, the uptake of CO₂ occurs through a transient phase and channels expansion. While the gas storage capacity of 1‘ is not very highH₂, 0.56 wt % and 0.010 kg H₂/L at 90 K and 900 Torr, and CO₂, 7.6 wt % at 273 K and 900 Torrthe guest molecules achieve very high densities, comparable to that of the liquid for H₂ (0.023 vs 0.021 molecules Å^-3) and to that of the solid for CO₂ (0.014 vs 0.022 molecules Å^-3). In addition, we have also studied the effect of the perturbation exerted by the guest molecules on its magnetic properties. The results show that while dehydration of 1 has negligible effect on its spin-canted antiferromagnetic behavior, CO₂ incorporation in the pores is responsible for an increment of the transition temperature at which the weak ferromagnetic ordering takes place from 22 to 29 K.