Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (25) Citing Articles via Google Scholar Google Scholar Articles by Wang, J. Articles by Kirkpatrick, R. J. Search for Related Content GeoRef GeoRef Citation

Interlayer structure and dynamics of Cl-bearing hydrotalcite: far infrared spectroscopy and molecular dynamics modeling

¹ Department of Geology, University of Illinois at Urbana-Champaign, 1301 W. Green St., Urbana, Illinois 61801, U.S.A.
² Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, K8-96, Richland, Washington 99352, U.S.A.

Correspondence: ^* E-mail: jwang7{at}uiuc.edu

Comparison of the observed far-infrared (FIR) spectrum of Cl^–-containing hydrotalcite, [Mg₃Al(OH)₈]Cl·3H₂O, to a power spectrum calculated using molecular dynamics (MD) computer simulation, provides a greatly increased understanding of the structure and vibrational dynamics in the interlayers of layered double hydroxides. Good agreement between the observed FIR band positions and the simulated power spectrum illustrates the capability of this combination of experimental and computational techniques to effectively probe the structure and dynamics of water in nano-pores and other confined spaces. The simulation model assumes an ordered Mg₃Al arrangement in the octahedral sheet and no constraints on the movement of any atoms or on the geometry and symmetry of the simulation supercell. Calculated anisotropic components of the individual atomic power spectra in combination with computed animations of the vibrational modes from normal mode analysis allow for reliable interpretations of the observed spectral bands. For the vibrations related to octahedral cation motions, bands near 145, 180, and 250 cm^–1 are due dominantly to Mg vibration in the c direction (perpendicular to the hydroxide layers), Al vibration in the c direction, and Mg and Al vibrations in the a-b plane (parallel to the hydroxide layers), respectively. The low frequency vibrational motions of the interlayer are controlled by a network of hydrogen bonds formed between interlayer water molecules, Cl^– ions, and the OH groups of the main hydroxide layers. The bands near 40–70 cm^–1 are related to the translational motions of interlayer Cl^– and H₂O in the a-b plane, and the bands near 120 cm^–1 and 210 cm^–1 are largely due to translational motions of the interlayer species in the c direction. The three librational modes of interlayer water molecules near 390, 450, and 540 cm^–1 correspond to twisting, rocking, and wagging hindered rotations, respectively. The spectral components of the interlayer Cl^– motions are remarkably similar to those of bulk aqueous chloride solutions, reflecting the structural and dynamic similarity of the nearest-neighbor Cl^– environments in the interlayer and in solution.

This article has been cited by other articles:

				P. S. Braterman and R. T. Cygan Vibrational spectroscopy of brucite: A molecular simulation investigation American Mineralogist, July 1, 2006; 91(7): 1188 - 1196. [Abstract] [Full Text] [PDF]

				R. J. Kirkpatrick, A. G. Kalinichev, and J. Wang Molecular dynamics modelling of hydrated mineral interlayers and surfaces: structure and dynamics Mineralogical Magazine, June 1, 2005; 69(3): 289 - 308. [Abstract] [Full Text] [PDF]