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.