Raman spectroscopic study of the antimonate mineral brandholzite Mg[Sb2(OH)12]•6H2O

Raman spectra of brandholzite Mg[Sb-2(OH)(12)]center dot 6H(2)O were studied, complemented with infrared spectra, and related to the structure of the mineral. An intense Raman sharp band at 618 cm(-1) is attributed to the SbO symmetric stretching mode. The low-intensity band at 730 cm(-1) is ascribed to the SbO antisymmetric stretching vibration. Low-intensity Raman bands were found at 503, 526 and 578 cm(-1). Corresponding infrared bands were observed at 527, 600, 637, 693, 741 and 788 cm(-1). Four Raman bands observed at 1043, 1092, 1160 and 1189 cm(-1) and eight infrared bands at 963, 1027, 1055, 1075, 1108, 1128, 1156 and 1196 cm(-1) are assigned to delta SbOH deformation modes. A complex pattern resulting from the overlapping band of the water and hydroxyl units is observed. Raman bands are observed at 3240, 3383, 3466, 3483 and 3552 cm(-1); infrared bands at 3248, 3434 and 3565 cm(-1). The Raman bands at 3240 and 3383 cm(-1) and the infrared band at 3248 cm(-1) are assigned to water-stretching vibrations. The two higher wavenumber Raman bands observed at 3466 and 3552 cm(-1) and two infrared bands at 3434 and 3565 cm(-1) are assigned to the stretching vibrations of the hydroxyl units. Observed Raman and infrared bands in the OH stretching region are associated with O-H center dot center dot center dot O hydrogen bonds and their lengths 2.72, 2.79, 2.86, 2.88 and 3.0 angstrom (Raman) and 2.73, 2.83 and 3.07 angstrom (infrared). Copyright (C) 2009 John Wiley & Sons, Ltd.