The effect of activation temperature on the textural properties and low-pressure adsorption performance of the porous coordination polymer Cu2(pzdc)2(bpy) [pzdc = pyrazine-2,3-dicarboxylate, bpy = 4,4′-bipyridine], better known as CPL-2, was considered to elucidate the material potential for separations. The effective activation temperature range was estimated via coupled thermal gravimetric and Fourier transforms infrared spectroscopy analysis. A textural property analysis via the αs-plot, Dubinin−Radushkevich and Horvath−Kawazoe methods show that a significant reduction in effective surface area and micropore volume occurs when the activation temperature is increased from 373 to 423 K. Cooling of the sample in a moisture-free environment revealed that such reduction is nonreversible, as evidenced by single-component CO2 equilibrium adsorption tests. Although CO2 equilibrium adsorption isotherms exhibit a linear behavior in the ambient pressure range, an increase in activation temperature eventually decreases the pore size of the structure resulting in a considerable decrease in loading amounts. This was also corroborated by means of in situ high-temperature X-ray diffraction, which was used to monitor the lattice semiquantitative changes of CPL-2 during the thermal activation sequence. In addition, adsorption uptake data was gathered to estimate a diffusion time constant and elucidate preliminary information about the kinetics involved during the transport of CO2 through the micropores of CPL-2. After inspection of the adsorbent particle morphology via scanning electron microscopy, it became ostensible that the transport phenomenological model suitable to fit the uptake data was that of a slab-shape particle. For the sample pretreated at 373 K the analysis yields an average diffusion time constant of ca. 0.5 s−1 at 298 K.

In situ high temperature X-ray diffraction, nitrogen porosimetry and gas adsorption at room temperature were used to elucidate the effect of the degassing or activation temperature on the long-range and micropore textural properties of a series of coordination polymers with pillared-layer structures. Ramp-and-soak thermal gravimetric analysis performed at selected activation temperatures were used to verify the thermal stability of a CPL-n series [Cu(2)(pzdc)(2)L; pzdc = pyrazine-2,3-dicarboxylate; L = 4,4-azopyridine (apy) for CPL-4, 1,2-di-(4-pyridil)-ethylene (bpe) for CPL-5, N-(4-pyridyl)-isonicotinamide (pia) for CPL-6, and 1,2-di-(4-pyridyl)-glycol (dpyg) for CPL-7]. Although the activation temperatures were far below the decomposition point of the complexes, these resulted in significant and unique changes in micropore surface area and volume, even for CPL-4, -5 and -6, which contained pillar ligands with similar dimensions and similar structural long-range order. For the case of CPL-7, however, the framework appeared to be non-porous at any given activation temperature. Pure component equilibrium adsorption data gathered for CO(2), CH(4), and N(2) were used to elucidate the CPL-n materials potential for storage and separations at room temperature. All of the materials exhibited considerable selectivity toward CO(2), particularly at moderate pressures. Meanwhile, CO(2) isosteric heats of adsorption indicated that the pore functionalities arising from the pillar ligands provided similar interactions with the adsorbate in the cases of CPL-4 and -5. For CPL-6, the presence of the carbonyl (C[double bond, length as m-dash]O) group appeared to enhance interactions with CO(2) at low loadings.

A nonreversible thermally induced pore contraction has been observed in the coordination polymer {Cu 2 (pzdc) 2 (bpy)} (pzdc = 2,3-pyrazinedicarboxylate; bpy = 4,4 0 -bipyridine), known as CPL-2. In an effort to understand this phenomenon, we have employed coupled differential scanning calorimetry and X-ray diffraction (DSC-XRD) and in situ 13 C crosspolarization magic angle spinning nuclear magnetic resonance (CP MAS NMR) measurements. DSC data showed no energetic transitions that would suggest a structural rearrangement of the crystalline sorbent, while small changes in the corresponding XRD patterns were probably related to the structural breathing mode upon the removal of water molecules. On the other hand, in situ high-temperature 13 C CP MAS NMR evidenced displacement of pzdc carbons upon an increase in temperature. Moreover, bpy pillar ligand resonance signals were only observed for samples pretreated at 423 K, both ex situ and in situ, probably indicating nonreversible local-range changes in the 1D channels of CPL-2. This temperature is well below the decomposition point of the framework, evidencing how sensible the material is to thermal preactivation. Careful analysis of the implications of employing thermal treatments for coordination polymers is crucial to elucidate the potential of these materials for adsorption and catalysis applications.

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Two related metal-organic frameworks (MOFs) based on trinuclear copper-pyrazolato structural building units (SBUs) connected by bipyridine linkers have been prepared and studied. A small chemical modification to the supporting pyrazolato ligands of a [Cu 3 ]-SBU results in two vastly different (three-fold vs eight-fold interpenetrated) MOF structures. The gas sorption properties of the two MOFs have been determined experimentally in the 0 to 10 atm pressure range. Both MOFs sorb CO 2 selectively over N 2 and H 2 , showing hysteretic sorption−desorption profiles. The hysteretic behavior is attributed to the structural flexibility of the lattices, probed by powder X-ray diffraction before and after CO 2 sorption. As the metal centers and hydroxy groups of the MOF surfaces are sterically hindered, the sorbed dipolar CO 2 molecules are attached with low sorption enthalpy to the organic groups, as determined by theoretical calculations.