Synthetic Mg/Zn/Al-hydrotalcites with atomic ratios of 6 : 0 : 2, 4 : 2 : 2, 2 : 4 : 2 and 0 : 6 : 2 were characterized by FT-Raman and FT-IR spectroscopy. 'Al-OH' IR translation modes are observed at 419, 427, 559, 616 and 771 cm −1 with two corresponding Raman bands at 465-477 and 547-553 cm −1 . 'Mg-OH' IR translation modes are found at 412, 559 and 616 cm −1 with equivalent Raman bands at 464-477 and 547-553 cm −1 . The 'Zn-OH' IR translation mode is found at 445 cm −1 and the Raman modes around 450 and 495 cm −1 . The CO 3 2− group is identified by the n 1 (IR) at 1112 cm −1 and a doublet in the Raman around 1045-1055 and 1060 cm −1 . n 2 (IR) is observed at 874 cm −1 . n 3 (IR) is a doublet at 1359 and 1381 cm −1 . n 4 is observed in both the IR and Raman spectra around 670 and 695-715 cm −1 , respectively. In the OH deformation region, a doublet is observed for 'Al-OH' at 955 and 1033 cm −1 in the IR spectra. The 'Zn-OH' IR deformation mode is observed at 1462 cm −1 . H 2 O is characterized by a bending mode at 1632 cm −1 and an H-bonded interlayer H 2 O mode at 3266 cm −1 with a Raman band between 3244 and 3271 cm −1 . The OH stretching region is characterized by three bands in the Raman spectra around 3355-3360, 3440-3455 and 3535-3580 cm −1 . One band is observed in the IR spectra at 3471 cm −1 .

The difference in the local environment of CO 3 2-, NO 3 -, SO 4 2-, and ClO 4in Mg/Al-hydrotalcite compared to the free anions was studied by infrared and Raman spectroscopy. In comparison to free CO 3 2a shift toward lower wavenumbers was observed. A band around 3000-3200 cm -1 has been attributed to the bridging mode H 2 O-CO 3 2-. The IR spectrum of CO 3hydrotalcite clearly shows the split n 3 band around 1365 and 1400 cm -1 together with weak n 2 and n 4 modes around 870 and 667 cm -1 . The n 1 mode is activated and observed as a weak band around 1012 cm -1 . The Raman spectrum shows a strong n 1 band at 1053 cm -1 plus weak n 3 and n 4 modes around 1403 and 695 cm -1 . The symmetry of the carbonate anions is lowered from D 3h to C 2s resulting in activation of the IR inactive n 1 mode around 1050-1060 cm -1 . In addition, the n 3 shows a splitting of 30-60 cm -1 . Although NO 3hydrotalcite has incorporated some CO 3 2the IR shows a strong n 3 mode at 1360 cm -1 with a weak band at 827 cm -1 , and the n 4 band is observed at 667 cm -1 , although it is largely obscured by the hydrotalcite lattice modes. The Raman spectrum shows a strong n 1 mode at 1044 cm -1 with a weaker n 4 band at 712 cm -1 . The n 3 mode at 1355 cm -1 is obscured by a broad band due to the presence of CO 3 2-. The symmetry of NO 3did not change when incorporated in hydrotalcite. The IR spectrum of SO 4 -hydrotalcite shows a strong n 3 at 1126, n 4 at 614 and a weak n 1 mode at 981 cm -1 . The Raman spectrum is characterized by a strong n 1 mode at 982 cm -1 plus medium n 2 and n 4 bands at 453 and 611 cm -1 ; n 3 cannot be identified as a separate band, although a broad band can be seen around 1134 cm -1 . The site symmetry of SO 4 2is lowered from T d to C 2v . The distortion of ClO 4in the interlayer of hydrotalcite is reflected in the IR spectrum with both n 3 and n 4 bands split around 1096 and 1145 cm -1 and 626 and 635 cm -1 , respectively. A weak n 1 band is observed at 935 cm -1 . The Raman spectrum shows a strong n 1 mode at 936 cm -1 plus n 2 and n 4 bands at 461 and 626 cm -1 , respectively. A n 3 mode cannot be clearly recognized, but a broad band is visible around 1110 cm -1 . These data indicative a lowering of symmetry from T d to C s .

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Lecontite, (NH 4 )Na(SO 4 ).2H 2 O, was synthesised at room temperature in high purity compared to earlier work with a minor impurity of mascagnite, (NH 4 ) 2 SO 4 . Rietveld refinement of the XRD results confirmed the crystal structure and unit cell dimensions as published earlier. Raman and Infrared spectroscopy, in conjunction with factor group analysis, resulted in a complex pattern of overlapping sulphate, NH and OH modes. The NH modes υ 1 was observed around 2880 cm -1 , υ 2 around 1700 cmoverlapping with water OH-bending modes, υ 3 around 3300 cm -1 overlapping with water OH-stretching modes around 3023, 3185 and 3422 cm -1 , and υ 4 around 1432, 1447 and 1462 cm -1 . The sulphate group in the crystal structure displays a decrease in symmetry from T d as evidenced by the activation of the ν 1 mode at 982 cm -1 and the ν 2 mode around 452 cm -1 in the Infrared spectrum. The υ 3 mode shows clear splitting in the infrared spectra with a strong band at 1064 cm -1 accompanied by two shoulders at 1107 and 1139 cm -1 . The Raman spectra show three weak bands at 1068, 1109 and 1135 cm -1 with a shoulder at 1155 cm -1 . Similar splitting was observed for the υ 4 mode around 611 and 632 cm -1 in the Infrared and Raman spectra, respectively.