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American Mineralogist; May 2002; v. 87; no. 5-6; p. 623-629
© 2002 Mineralogical Society of America
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Infrared and Raman study of interlayer anions CO32–, NO3–, SO42– and ClO4– in Mg/Al-hydrotalcite

J. Theo Kloprogge*, David Wharton, Leisel Hickey and Ray L. Frost

Centre for Instrumental and Developmental Chemistry, Queensland University of Technology, 2 George Street, GPO Box 2434, Brisbane Qld 4001, Australia

Correspondence: * E-mail: t.kloprogge{at}qut.edu.au

The difference in the local environment of CO32–, NO3–, SO42–, and ClO4– in Mg/Al-hydrotalcite compared to the free anions was studied by infrared and Raman spectroscopy. In comparison to free CO32– a shift toward lower wavenumbers was observed. A band around 3000–3200 cm–1 has been attributed to the bridging mode H2O-CO32–. The IR spectrum of CO3– hydrotalcite clearly shows the split {nu}3 band around 1365 and 1400 cm–1 together with weak {nu}2 and {nu}4 modes around 870 and 667 cm–1. The {nu}1 mode is activated and observed as a weak band around 1012 cm–1. The Raman spectrum shows a strong {nu}1 band at 1053 cm–1 plus weak {nu}3 and {nu}4 modes around 1403 and 695 cm–1. The symmetry of the carbonate anions is lowered from D3h to C2s resulting in activation of the IR inactive {nu}1 mode around 1050–1060 cm–1. In addition, the {nu}3 shows a splitting of 30–60 cm–1. Although NO3-hydrotalcite has incorporated some CO32– the IR shows a strong {nu}3 mode at 1360 cm–1 with a weak band at 827 cm–1, and the {nu}4 band is observed at 667 cm–1, although it is largely obscured by the hydrotalcite lattice modes. The Raman spectrum shows a strong {nu}1 mode at 1044 cm–1 with a weaker {nu}4 band at 712 cm–1. The {nu}3 mode at 1355 cm–1 is obscured by a broad band due to the presence of CO32–. The symmetry of NO3– did not change when incorporated in hydrotalcite. The IR spectrum of SO4-hydrotalcite shows a strong {nu}3 at 1126, {nu}4 at 614 and a weak {nu}1 mode at 981 cm–1. The Raman spectrum is characterized by a strong {nu}1 mode at 982 cm–1 plus medium {nu}2 and {nu}4 bands at 453 and 611 cm–1; {nu}3 cannot be identified as a separate band, although a broad band can be seen around 1134 cm–1. The site symmetry of SO42– is lowered from Td to C2v. The distortion of ClO4– in the interlayer of hydrotalcite is reflected in the IR spectrum with both {nu}3 and {nu}4 bands split around 1096 and 1145 cm–1 and 626 and 635 cm–1, respectively. A weak {nu}1 band is observed at 935 cm–1. The Raman spectrum shows a strong {nu}1 mode at 936 cm–1 plus {nu}2 and {nu}4 bands at 461 and 626 cm–1, respectively. A {nu}3 mode cannot be clearly recognized, but a broad band is visible around 1110 cm–1. These data indicative a lowering of symmetry from Td to Cs.






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