A series of solid sodium (hydroxy)aluminates has been prepared from highly caustic aqueous sodium aluminate solutions. The coordination geometry of the aluminum in these compounds was established by 27 Al magic angle spinning nuclear magnetic resonance (27 Al-MAS-NMR) spectroscopy and was used to identify the Raman and IR vibration frequencies characteristic of tetrahedral (Raman: 440 cm-1; IR: 823 cm-1 and 540 cm-1) and octahedral (Raman: 490- 500 cm-1; IR: 728 cm-1) aluminum sites. The vibrational spectra of these solids differ markedly from those observed for concentrated aqueous solutions, and it appears that solid-state vibrational spectra cannot be used to predict the structure of aluminate species existing in solutions.
H. R. Watling, P. M. Sipos, L. Byrne, G. T. Hefter, and P. M. May, "Raman, IR, and 27 Al-MAS-NMR Spectroscopic Studies of Sodium (Hydroxy)aluminates," Appl. Spectrosc. 53, 415-422 (1999)