A simple reaction scheme based on the heterogeneous intercalation of pillaring ligands (HIPLs) provides a convenient method for systematically tuning pore size, pore functionality, and network flexibility in an extended series of pillared cyanonickelates (PICNICs), commonly referred to as Hofmann compounds. The versatility of the approach is demonstrated through the preparation of over 40 different PICNICs containing pillar ligands ranging from ∼4 to ∼15 Å in length and modified with a wide range of functional groups, including fluoro, aldehyde, alkylamine, alkyl, aryl, trifluoromethyl, ester, nitro, ether, and nonmetalated 4,4'-bipyrimidine. The HIPL method involves reaction of a suspension of preformed polymeric sheets of powdered anhydrous nickel cyanide with an appropriate pillar ligand in refluxing organic solvent, resulting in the conversion of the planar [Ni2(CN)4]n networks into polycrystalline three-dimensional porous frameworks containing the organic pillar ligand. Preliminary investigations indicate that the HIPL reaction is also amenable to forming Co(L)Ni(CN)4, Fe(L)Ni(CN)4, and Fe(L)Pd(CN)4 networks. The materials show variable adsorption behavior for CO2 depending on the pillar length and pillar functionalization. Several compounds show structurally flexible behavior during the adsorption and desorption of CO2. Interestingly, the newly discovered flexible compounds include two flexible Fe(L)Ni(CN)4 derivatives that are structurally related to previously reported porous spin-crossover compounds. The preparations of 20 pillar ligands based on ring-functionalized 4,4'-dipyridyls, 1,4-bis(4-pyridyl)benzenes, and N-(4-pyridyl)isonicotinamides are also described.
A detailed correlation is presented between the in situ Fourier transform-infrared (FT-IR) spectra of adsorbed CO2, CuBzPyz host bands, and CO2 adsorption sites using previously reported crystal structures of CO2-loaded CuBzPyz and CO2 adsorption isotherms. Through the analysis of both in situ attenuated total reflectance FT-IR spectra taken at several points on the high pressure isotherm and in situ transmission FT-IR spectra acquired at low pressures and cryogenic temperatures, we provide additional insight into the pore-filling mechanism of CO2 on the structurally dynamic CuBzPyz host. The FT-IR spectrum of adsorbed CO2 shows distinct ν2 and ν3 spectral features that can be attributed to known CO2 adsorption sites observed in the reported crystal structure of the CO2-saturated phase of CuBzPyz. The availability of detailed high quality CO2-loaded structural data for CuBzPyz makes this system a case study for associating infrared spectral features with CO2 adsorption sites and should prove valuable for future interpretations of CO2 host−guest and guest−guest interactions when X-ray quality structural data is unavailable.
Flexibility provides selectivity: The selective adsorption of CO2 from mixtures with N2, CH4, and N2O in a dynamic porous coordination polymer (see monomer structure) was evaluated by ATR‐FTIR spectroscopy, GC, and SANS. All three techniques indicate highly selective adsorption of CO2 from CO2/CH4 and CO2/N2 mixtures at 30 °C, with no selectivity observed for the CO2/N2O system.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.