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Dynamics of water molecules in VPI-5 and AlPO_4-5 studied by deuterium NMR spectroscopy

Goldfarb, Daniella and Li, Hong Xin and Davis, Mark E. (1992) Dynamics of water molecules in VPI-5 and AlPO_4-5 studied by deuterium NMR spectroscopy. Journal of the American Chemical Society, 114 (10). pp. 3690-3697. ISSN 0002-7863. doi:10.1021/ja00036a018.

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The dynamic properties of water and ammonia within the channels of VPI-5 and AlPO_4-5 were studied by ^2H NMR spectroscopy over a wide range of temperatures. The results were correlated with the corresponding ^(27)Al MAS NMR spectra. In both materials two distinct types of water molecules were detected, bound molecules and physisorbed molecules undergoing isotropic reorientation within the channels. The bound molecules were assigned to molecules coordinated to framework Al undergoing some local motion. In AlPO_4-5 the line shape changes were reproduced by using a dynamic model of a two-site exchange where one site corresponds to the bound water and the second to the free water molecules. The relative populations of the two sites were found to be temperature dependent. In VPI-5 the water exhibits a higher degree of order and the two-site jump between free and bound molecules is associated with an additional 3-fold-site jump, resulting in a 6-site system. In this case the relative populations are temperature independent within the temperature range of 0-60 °C. Three types of ND_3 molecules were distinguished in VPI-5 adsorbed with ammonia: physisorbed molecules, bound molecules undergoing a rotation about the N-A1 axis, and rigid molecules. No exchange takes place between these three states within the NMR time scale.

Item Type:Article
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URLURL TypeDescription
Goldfarb, Daniella0000-0001-5714-7159
Davis, Mark E.0000-0001-8294-1477
Alternate Title:Dynamics of water molecules in VPI-5 and AlPO4-5 studied by deuterium NMR spectroscopy
Additional Information:© 1992 American Chemical Society. Received August 12, 1991. This study was made possible by funds granted to D.G. through a fellowship program sponsored by the Charles H. Revson Foundation. We thank K. Zukerman for sample preparation and A. J. Vega and R. Poupko for very helpful discussions. We also thank L. McCusker and co-workers for making the preprint of their work available to us.
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Charles H. Revson FoundationUNSPECIFIED
Issue or Number:10
Record Number:CaltechAUTHORS:20180724-152025542
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Official Citation:Dynamics of water molecules in VPI-5 and AlPO4-5 studied by deuterium NMR spectroscopy Daniella Goldfarb, Hong Xin Li, and Mark E. Davis Journal of the American Chemical Society 1992 114 (10), 3690-3697 DOI: 10.1021/ja00036a018
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:88216
Deposited By: George Porter
Deposited On:25 Jul 2018 16:51
Last Modified:16 Nov 2021 00:24

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