期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 130, 期 37, 页码 12427-12434出版社
AMER CHEMICAL SOC
DOI: 10.1021/ja802474b
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资金
- National Energy Technology Laboratory [DE-AC26-04NT41817]
- Oak Ridge Institute for Scientific Education (ORISE)
Rare hysteretic adsorption/desorption isotherms are reported for CO2 and N-2 on a pillared Ni(1,2-bis(4-pyridyl)ethylene)[Ni(CN)(4)] compound (NiBpeneNiCN). The hysteresis occurs under moderate pressure and at temperatures above the critical temperatures of the respective gases. Powder X-ray diffraction measurements indicate that the material is an extended three-dimensional analogue of the well-known Hofmann clathrates which is formed through axial bridging of the in-plane octahedral Ni sites by the bidentate 1,2-bis(4-pyridyl) ethylene. The hysteretic behavior toward guest adsorption and desorption is attributed to a structural phase transition in the material resulting from a variation in the tilt angle of the 1,2-bis(4-pyridyl)ethylene pillars. Kinetics studies on the desorption of acetone from the material show two first-order processes with two rate constants yielding activation energies of 68 and 55 kJ/mol when loadings are greater than 1 equiv of acetone per formula unit. The CO2 adsorption/desorption isotherms on the series of structurally similar Ni(L)[Ni(CN)(4)] compounds, where L = pyrazine, 4,4'-bipyridine, 1,2-bis(4-pyridyl)ethane, and dipyridylacetylene, are also reported. In contrast to NiBpeneNiCN, the rigid members of this series show normal type I isotherms with no measureable hysteresis and no significant structural changes during the adsorption/desorption cycle, while the flexible 1,2-bis(4-pyridyl)ethane-bridged sample collapses in the guest-free state and shows no significant adsorption of CO2.
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