Abstract
In this thesis, a new organic-inorganic hybrid framework, A1, bearing oxalate (C2O42－) and formate (HCOO－) in aluminum phosphite lattice, has been synthesized under mild hydrothermal conditions and showed carbon dioxide adsorption property. The large channels located in the structure of A1 are similar to the nanotubules in the gallium oxalatophosphite of NTHU-7. By replacing gallium for aluminum in the reactions, three isostructures A2, A3 and A4 were produced. All four compounds were characterized by single-crystal X-ray diffraction methods. The sample purity for each of the compounds was confirmed by powder X-ray diffraction before gas sorption and other property measurements. The chemical formula for A1 was determined to be [(H6peha)0.17(H2O)1.5][Al2(HPO3)2(C2O4)(HCOO)], where peha = pentaethylenehexamine. The hybrid framework consists of [Al2(HPO3)2]2+ 4-ring ladder chains interlinked by oxalate and formate groups into two types of channels, one with 4.8 Å in aperture and the other with 8.5 Å. The template H6peha6+ ions and lattice H2O in structure could not clearly elucidate from single-crystal data but were corroborated by the results of combined solid-state 13C NMR, TGA and EA data. The large template ions should reside in the larger channels and lattice waters in the smaller channels, as confirmed by the results from structure analysis on a high-temperature single-crystal X-ray diffraction data measured at 400 K. Compound A2, a gallium analogue of A1, is very similar to NTHU-7 in structure, A3 and A4 bear the same hybrid framework as A2 except template ions. In the structures of A1 to A4, residual electron densities were located between the smaller channels that could not be neglected to complete the structure refinements. They were primarily identified as formate groups which connected smaller channels to surround into the larger channels, giving rise to the final 3D structure. DEPT C-NMR data measured from reaction filtrates of A1 to A4 revealed the presence of formate anions, indicating the likelihood of in situ formation during reaction. Solid-state 1H NMR measurements as well confirmed formate groups in the structure. Gas sorption experiments were conducted on the two analouges A1 and A2. They showed affinity for carbon dioxide but were not high. The CO2 uptakes for A1 and A2 were 10.48 cm3/g and 2.90 cm3/g, respectively. The increased adsorption capacity for A1 should partially attribute to the lower density of Al-analogue.