Design of novel bilayer compounds of the CPO-8 type containing 1D channels

Article abstract of DOI:10.1021/ic050662v

The reaction between Zn(NO₃)₂·6H₂O and 5-aminoisophthalic acid (aip) in a mixture of diethylformamide (DEF) and ethanol resulted in [Zn(C₈H₅NO₄)(C ₅H₁₁NO)]_n (CPO-8-DEF). This compound is composed of infinite 2D layers with tetrahedral Zn atoms and aip ligands in a triangular topology. The DEF molecules are bonded to Zn, and within each layer, the DEF molecules are oriented in the same direction, while in the subsequent layer, the DEF molecules are oriented in the opposite direction. By introduction of the pillaring ligands 4,4-bipyridine (BPY), 1,2-di-4-pyridylethylene (DPE), 1,2-di-4-pyridylethane (DPA), and 1,3-di-4-pyridylpropane (DPP) into mixtures of N,N′-dimethylformamide and water with Zn(NO₃)₂ and aip, we have successfully synthesized a series of related pillared bilayer compounds with the same common triangular Zn(aip) layer structural motif as that observed in CPO-8-DEF. The compounds are denoted as CPO-8-BPY ([Zn(C ₈H₅NO₄)(C₁₀H₈N ₂)_0.5]_n·3nH₂O), CPO-8-DPE ([Zn(C₈H₅NO₄)-(C₁₂H ₁₀N₂)_0.5]_n·2.5nH ₂O), CPO-8-DPA ([Zn(C₈H₅NO₄)(C ₁₂H₁₂N₂)_0.5]_n·2. 5nH₂O), and CPO-8-DPP ([Zn(C₈H₅NO ₄)-(C₁₃H₁₄N₂)_0.5] _n·3nH₂O). In all cases, the pillars create spaces inside the bilayers that result in 1D channels running along the [010] directions with dimensions of 3.5 x 6.7 A². These channels contain water molecules that can be removed on heating to 150°C, resulting in porous structures. The crystal structures of these porous high-temperature variants have been determined on the basis of powder X-ray diffraction data. All of the compounds show preferential adsorption of H₂ over N ₂ at 77 K.