Raman, IR, and Al-27-MAS-NMR spectroscopic studies of sodium (hydroxy)aluminates

A series of solid sodium (hydroxy)aluminates has been prepared from highly caustic aqueous sodium aluminate solutions, The coordination geometry of th e aluminum in these compounds was established by Al-27 magic angle spinning nuclear magnetic resonance (Al-27-MAS-NMR) spectroscopy and was used to id entify the Raman and IR vibration frequencies characteristic of tetrahedral (Raman: 440 cm(-1); IR: 823 cm(-1) and 540 cm(-1)) and octahedral(Raman: 4 90-500 cm(-1); IR: 728 cm(-1)) aluminum sites. The vibrational spectra of t hese solids differ markedly from those observed for concentrated aqueous so lutions, and it appears that solid-state vibrational spectra cannot be used to predict the structure of aluminate species existing in solutions.