Infrared absorption spectra of the ¹⁸O-labeled acetylacetonates of Cr(III) and Mn(III)

The ¹⁸O-induced isotopic shifts of the Cr(III) and Mn(III) acetylacetonate (of over 90 at %¹⁸O) infrared absorption bands were measured in the 400-1650-cm^-1 region. The hitherto accepted assignments of these bands are discussed in the light of these measurements. It is found that the band at about 1520 cm^-1 is due to C=C stretching while that at about 1570 cm^-1 has a C=O stretching character. The ∼1425-cm^-1 band must be due to the asymmetrical CH₃ bending while the one at 661 cm^-1 probably belongs to an out-of-plane deformation and that at 590 cm^-1 to an M-O stretching.