Vibrational spectroscopic study of the sulphate mineral glaucocerinite (Zn,Cu)(10)Al(6)(SO(4))(3)(OH)(32)⋅18H(2)O - a natural layered double hydroxide.

We have studied the molecular structure of the mineral glaucocerinite (Zn,Cu)(5)Al(3)(SO(4))1.5(OH)16⋅9(H2O) using a combination of Raman and infrared spectroscopy. The mineral is one of the hydrotalcite supergroup of natural layered double hydroxides. The Raman spectrum is characterised by an intense Raman band at 982cm(-1) with a low intensity band at 1083cm(-1). These bands are attributed to the sulphate symmetric and antisymmetric stretching mode. The infrared spectrum is quite broad with a peak at 1020cm(-1). A series of Raman bands at 546, 584, 602, 625 and 651cm(-1) are assigned to the ν4 (SO4)(2)(-) bending modes. The observation of multiple bands provides evidence for the reduction in symmetry of the sulphate anion from Td to C2v or even lower symmetry. The Raman band at 762cm(-1) is attributed to a hydroxyl deformation mode associated with AlOH units. Vibrational spectroscopy enables aspects of the molecular structure of glaucocerinite to be determined.