Raman spectroscopic study of the schmiederite Pb₂Cu₂[(OH)₄|SeO₃|SeO₄]

Abstract

Abstract Raman spectroscopy lends itself to the studies of selenites, selenates, tellurites and tellurates as well as related minerals. The mineral schmiederite Pb 2 Cu 2 [(OH) 4 |SeO 3 |SeO 4 ], is interesting, in that, both selenite and selenate anions occur in the structure. Raman bands of schmiederite at 1095 and 934 cm −1 are assigned to the symmetric and antisymmetric mode of the (SeO 4 ) 2− anions. For selenites, the symmetric stretching mode occurs at a higher position than the antisymmetric stretching mode, as is evidenced in the Raman spectrum of schmiederite. The band at 834 cm −1 is assigned to the symmetric (SeO 3 ) 2− units. The two bands at 764 and 739 cm −1 are attributed to the antisymmetric (SeO 3 ) 2− units. An intense, sharp band at 398 cm −1 is assigned to the ν 2 bending mode. The two bands at 1576 and 1604 cm −1 are assigned to the deformation modes of the OH units. The observation of multiple OH bands supports the concept of a much distorted structure. This is based upon the four OH units coordinating the copper in a square planar structure. A single symmetric Raman band is observed at 3428 cm −1 and is assigned to the symmetric stretching mode of the OH units. The observation of multiple infrared OH stretching bands supports the concept of non‐equivalent OH units in the schmiederite structure. Copyright © 2008 John Wiley & Sons, Ltd.