Abstract: The IRspectrum and ¹¹B and ²⁷Al MAS NMR spectra of Al₁₈B₄O₃₃ are presented and discussed in relation to the possible existence of boron atoms substituting for aluminum atoms.The IRspectrum shows that the strong vibrations of the BO₃ groups are present in the 1500～1200 cm^-1 region, and very weak bands of BO₄ units are present in the region from 1000 to 1100 cm^-1.¹¹B MAS NMR spectrum indicates that the strong signal for BO₃ units appears in the region from δ+5 to δ+20, and the very weak signal for BO₄ units is at about δ- 1, while ²⁷Al MAS NMR spectrum shows five peaks at about δ+62, +42.1, +14, -4.7 and -6.4, originating from AlO₄, AlO₄, AlO₅, AlO₆ and AlO₆, respectively.These results reveal that there are minor BO₄ units in Al₁₈B₄O₃₃, indicating that a small amount of Batoms substitute for Al atoms in the 4-fold coordination.

Key words: Al₁₈B₄O₃₃, IR spectrum, ¹¹B, ²⁷Al MAS NMR spectrum