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The mineral nesquehonite Mg(OH)(HCO(3))·2H(2)O has been analysed by a combination of infrared (IR) and infrared emission spectroscopy (IES). Both techniques show OH vibrations, both stretching and deformation modes. IES proves the OH units are stable up to 450°C. The strong IR band at 934 cm(-1) is evidence for MgOH deformation modes supporting the concept of HCO(3)(-) units in the molecular structure. Infrared bands at 1027, 1052 and 1098 cm(-1) are attributed to the symmetric stretching modes of HCO(3)(-) and CO(3)(2-) units. Infrared bands at 1419, 1439, 1511, and 1528 cm(-1) are assigned to the antisymmetric stretching modes of CO(3)(2-) and HCO(3)(-) units. IES supported by thermoanalytical results defines the thermal stability of nesquehonite. IES defines the changes in the molecular structure of nesquehonite with temperature. The results of IR and IES supports the concept that the formula of nesquehonite is better defined as Mg(OH)(HCO(3))·2H(2)O.

Raman spectroscopy has been used to characterise synthetic mixed carbonate and molybdate hydrotalcites of formula Mg 6 Al 2 (OH) 16 ((CO 3 ) 2− ,(MoO 4 ) 2− )·4H 2 O. The spectra have been used to assess the molecular assembly of the cations and anions in the hydrotalcite structure. The spectra may be conveniently subdivided into spectral features on the basis of the carbonate anion, the molybdate anion, the hydroxyl units and water units. Bands are assigned to the hydroxyl stretching vibrations of water. Three types of carbonate anions are identified: (1) carbonate hydrogen-bonded to water in the interlayer, (2) carbonate hydrogen-bonded to the hydrotalcite hydroxyl surface, (3) free carbonate anions. It is proposed that the water is highly structured in the hydrotalcite, as it is hydrogen bonded to both the carbonate and the hydroxyl surface. The spectra have been used to assess the contamination of carbonate in an open reaction vessel in the synthesis of a molybdate hydrotalcite of formula Mg 6 Al 2 (OH) 16 ((CO 3 ) 2− , (MoO 4 ) 2− )·4H 2 O. Bands are assigned to carbonate and molybdate anions in the Raman spectra. Importantly, the synthesis of hydrotalcites from solutions containing molybdate provides a mechanism for the removal of this oxy-anion.

Raman spectroscopy has been used to study vanadates inthe solid state. The molecular structure of the vanadate minerals vésigniéite [BaCu 3 (VO 4 ) 2 (OH) 2 ] and volborthite [Cu 3 V 2 O 7 (OH) 2 ·2H 2 O] have been studied by Raman spectroscopy and infrared spectroscopy. The spectra are related to the structure of the two minerals. The Raman spectrum of vésigniéite is characterized by two intense bands at 821 and 856 cm −1 assigned to ν 1 (VO 4 ) 3− symmetric stretching modes. A series of infrared bands at 755, 787 and 899 cm −1 are assigned to the ν 3 (VO 4 ) 3− antisymmetric stretching vibrational mode. Raman bands at 307 and 332 cm −1 and at 466 and 511 cm −1 are assigned to the ν 2 and ν 4 (VO 4 ) 3− bending modes. The Raman spectrum of volborthite is characterized by the strong band at 888 cm −1 , assigned to the ν 1 (VO 3 ) symmetric stretching vibrations. Raman bands at 858 and 749 cm −1 are assigned to the ν 3 (VO 3 ) antisymmetric stretching vibrations; those at 814 cm −1 to the ν 3 (VOV) antisymmetric vibrations; that at 508 cm −1 to the ν 1 (VOV) symmetric stretching vibration and those at 442 and 476 cm −1 and 347 and 308 cm −1 to the ν 4 (VO 3 ) and ν 2 (VO 3 ) bending vibrations, respectively. The spectra of vésigniéite and volborthite are similar, especially in the region of skeletal vibrations, even though their crystal structures differ.

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