An FT-Raman Spectroscopic Study of the Conformational Properties of Chlorocyclohexane in Zeolites

• Published in: The journal of physical chemistry. B Vol. 107; no. 31; pp. 7647 - 7653
• Main Authors: Huang, Yining, Leech, James H
• Format: Journal Article
• Language: English
• Published: American Chemical Society 07-08-2003
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp030194f

The conformational behavior of chlorocyclohexane (ClCH) adsorbed inside several representative zeolites such as completely siliceous ZSM-5, Na−Y, and siliceous Y (Si−Y) has been investigated by FT-Raman spectroscopy. The results have clearly shown that the conformational and dynamic properties of ClCH depend on the zeolitic framework structure, the presence of charge-balancing cations, as well as the Si/Al ratio. Compared to pure liquid, the population of equatorial conformation increases upon adsorption into ZSM-5. Apparently, the ZSM-5 framework stabilizes the equatorial conformation (with a larger molecular volume) via maximizing the van der Waals interactions between the host and guest. Within the ZSM-5 framework, the axial and equatorial conformers are still in dynamic equilibrium. It continues to shift toward the equatorial configuration upon lowering the temperature, and at 153 K the ClCH in ZSM-5 adopts the equatorial conformation exclusively. For the ClCH/Na−Y system, the situation is remarkably different. Upon incorporation of ClCH into Na−Y, the conformation of ClCH is immediately frozen as a result of very strong interaction with Na+ ions. The sorbate−cation interactions also lock the ClCH molecules into different orientations which vary from cage to cage, yielding a static disorder. However, if ClCH molecules are adsorbed in a Si−Y where the cation−sorbate interactions are lacking, the dynamic equilibrium between axial and equatorial conformation can be resumed. The relative population of equatorial conformer in Si−Y is higher than that in ZSM-5. The slightly larger equatorial concentration is attributed to the orderly packing of ClCH inside the supercage of Si−Y.