Infra-red spectra of the crystalline inorganic aluminates

The infra-red absorption spectra of fourteen inorganic anhydrous crystalline aluminates were obtained in the 10·5–24·5 μ range. These data were interpreted in terms of crystal structure of the compounds. Four-fold co-ordinated aluminium AlO4 tetrahedra can be identified by the presence of an intense broad absorption maxima in the 900-775 cm−1 region and a medium to strong absorption band between 675 and 575 cm−1, but no strong absorption around 740 cm−1. The AlO6 octahedra found in the aluminates with a spinel structure will exhibit strong absorption maxima around 760 and 670 cm−1, but will not show an absorption band above 800 cm−1. Aluminates with the elongated AlO6 octahedra which contain planar AlO4 groups have a strong complex band envelope above 775 cm−1 and a sharp strong band at 740 cm−1 in their infra-red spectra.