Raman spectroscopy of synthetic and natural iowaite

The chemistry of a magnesium based hydrotalcite known as iowaite Mg6Fe2Cl2(OH)16·4H2O has been studied using Raman spectroscopy. Iowaite has chloride as the counter anion in the interlayer. The formula of synthetic iowaite was found to be Mg5.78Fe2.09(Cl,(CO3)0.5)(OH)16·4H2O. Oxidation of natural iowaite results in the formation of Mg4FeO(Cl,CO3) (OH)8·4H2O. X-ray diffraction (XRD) shows that the iowaite is a layered structure with a d(0 0 1) spacing of 8.0 Å. For synthetic iowaite three Raman bands at 1376, 1194 and 1084 cm−1 are attributed to CO3 stretching vibrations. These bands are not observed for the natural iowaite but are observed when the natural iowaite is exposed to air. The Raman spectrum of natural iowaite shows three bands at 708, 690 and 620 cm−1 and upon exposure to air, two broad bands are found at 710 and 648 cm−1. The Raman spectrum of synthetic iowaite has a very broad band at 712 cm−1. The Raman spectrum of natural iowaite shows an intense band at 527 cm−1. The air oxidized iowaite shows two bands at 547 and 484 cm−1 attributed to the (CO3)2−ν2 bending mode. Raman spectroscopy has proven most useful for the study of the chemistry of iowaite and chemical changes induced in natural iowaite upon exposure to air.