Orientation and Motion of Interlamellar Water: An Infrared and NMR Investigation of Water in the Galleries of Layered {Cd_0._7_5}{PS_3}{K_0._5}{(H_2O)}{_y}

Arun, Narayanaswamy and Vasudevan, Sukumaran and Ramanathan, Krishna Venkatachala (2000) Orientation and Motion of Interlamellar Water: An Infrared and NMR Investigation of Water in the Galleries of Layered {Cd_0._7_5}{PS_3}{K_0._5}{(H_2O)}{_y}. In: Journal of the American Chemical Society, 122 (25). pp. 6028-6038.

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Abstract

The motion of water in the galleries of layered {Cd_0._7_5PS_3K_0._5}{(H_2O)}{_1._2}, prepared by the ion-exchange intercalation of hydrated potassium ions into {CdPS_3}, have been investigated using a combination of orientation dependent NMR and infrared (TR) spectroscopies asa function of temperature. Within the galleries of the intercalated compound the potassium ions are displaced toward the layers and are immobile, while the water molecules form monolayer-thick two-dimensional islands. Two types of interlamellar water are distinguishable by both NMR and IR spectroscopy. A loosely bound isotropically tumbling water which is easily lost on mild evacuation and a more tightly bound water with restricted degrees of rotational freedom. The angular dependence of the NMR and IR spectral features of the latter indicate that their \overrightarrow{C_2} symmetry axis is at a fixed orientation with respect to the interlamellar normal and rotate rapidly about it. In analogy with bulk aqueous solutions these two types of interlamellar water may be considered as two-dimensional solventlike water and water coordinated to the potassium ion forming part of its hydration shell. A remarkable feature of the water in the galleries of {Cd_0._7_5PS_3K_0._5}{(H_2O)}{_1._2}, is the extremely slow rate of exchange (\tau >> {10-5})s) between the two-dimensional solventlike water and the coordinated water, in direct contrast to the rapid exchange observed for K ions in bulk aqueous solutions. The present experimental results provide the first observation of the effect of confinement on solvation shell exchange. It is suggested that the slowing down could be the effect of confinement in two dimension which would strongly inhibit any mechanism involving transition or intermediate states which require an expansion of the coordination shell around the potassium ion.

Item Type:	Journal Article
Publication:	Journal of the American Chemical Society
Publisher:	American Chemical Society
Additional Information:	Copyright of this article belongs to American Chemical Society.
Department/Centre:	Division of Chemical Sciences > Sophisticated Instruments Facility (Continued as NMR Research Centre) Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited:	04 Nov 2009 07:36
Last Modified:	19 Sep 2010 05:00
URI:	http://eprints.iisc.ac.in/id/eprint/18089

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