H2, N2, CO, and CO2 are readily incorporated in the porous, 3D sodalitic frameworks of coordination polymers of the [ML2]n type, with M = Pd(II) or Cu(II) and HL = 2-hydroxypyrimidine or 4-hydroxypyrimidine. The metal ion and ligand functionalization modulate their sorption properties, making these materials suitable for gas storage and separation purposes.

Reaction of CuX 2 (X ) NO 3 , Cl, (SO 4 ) 1/2 ) salts and Hpymo‚HX (Hpymo ) 2-hydroxypyrimidine; X ) Cl, NO 3 ) in aqueous amine solutions (amine ) NH 3 , CH 3 NH 2 ) leads to formation of the poorly crystalline three-dimensional open-framework coordination polymer [Cu(pymo-N1,N3) 2 ] ∞ (1). Under the same reaction conditions, but in the presence of amine and group 1 metal salts of single charged voluminous anions, highly crystalline clathrates of the type) are obtained. The X-ray crystal structure of 1‚NH 4 ClO 4 reveals that the combination of square-planar Cu 2+ ion with 120°bond angles provided by Hpymo generates a three-dimensional porous [Cu-(pymo-N1,N3) 2 ] ∞ framework with ammonium and perchlorate ions and water molecules included in the pores. 1 possesses a rich host-guest chemistry. Indeed, N 2 sorption at 77 K by empty host 1 reveals its microporous nature with a BET surface area of ca. 200 m 2 g -1 . Hydrated 1 loses water upon heating and when exposed to moist air regenerates the original hydrated material. Likewise, 1‚NH 4 ClO 4 loses ammonia upon heating, giving the corresponding activated acidic material 1‚HClO 4 which upon exposure to gaseous ammonia regenerates 1‚NH 4 ClO 4 . In addition, 1 reversibly and selectively sorbs AClO 4 salts (A ) NH 4 , Li, Na, K, Rb) when exposed to AClO 4 aqueous solutions giving highly crystalline 1‚AClO 4 clathrates. Cl -, NO 3 -, SiF 6 2-, and SO 4 2salts are, however, not taken up. Salt sorption curves are of type V and possess hysteresis loops. This behavior agrees with the observed guest-induced structure phase change taking place in the 1 framework after guest inclusion.

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 A 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 high-H2, 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 Torr-the guest molecules achieve very high densities, comparable to that of the liquid for H2 (0.023 vs 0.021 molecules A-3) and to that of the solid for CO2 (0.014 vs 0.022 molecules A-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.