Single‐crystal Raman spectroscopy of brandholzite Mg[Sb(OH) 6 ] 2 •6H 2 O and bottinoite Ni[Sb(OH) 6 ] 2 • 6H 2 O and the polycrystalline Raman spectrum of mopungite Na[Sb(OH) 6 ]

The single‐crystal Raman spectra of minerals brandholzite and bottinoite, formula M[Sb(OH) 6 ] 2 •6H 2 O, where M is Mg +2 and Ni +2 , respectively, and the non‐aligned Raman spectrum of mopungite, formula Na[Sb(OH) 6 ], are presented for the first time. The mixed metal minerals comprise alternating layers of [Sb(OH) 6 ] −1 octahedra and mixed [M(H 2 O) 6 ] +2 /[Sb(OH) 6 ] −1 octahedra. Mopungite comprises hydrogen‐bonded layers of [Sb(OH) 6 ] −1 octahedra linked within the layer by Na + ions. The spectra of the three minerals were dominated by the SbO symmetric stretch of the [Sb(OH) 6 ] −1 octahedron, which occurs at approximately 620 cm −1 . The Raman spectrum of mopungite showed many similarities to spectra of the di‐octahedral minerals, supporting the view that the Sb octahedra give rise to most of the Raman bands observed, particularly below 1200 cm −1 . Assignments have been proposed on the basis of the spectral comparison between the minerals, prior literature and density functional theory (DFT) calculations of the vibrational spectra of the free [Sb(OH) 6 ] −1 and [M(H 2 O) 6 ] +2 octahedra by a model chemistry of B3LYP/6‐31G(d) and lanl2dz for the Sb atom. The single‐crystal spectra showed good mode separation, allowing most of the bands to be assigned to the symmetry species A or E . Copyright © 2010 John Wiley & Sons, Ltd.