RECENTLY, many papers1 have been published on the infra-red spectra of metal chelate compounds of β-diketones in the sodium chloride (4,000 ∼ 650 cm.−1) region. The empirical assignments of the observed bands have also been made by Locomte and other workers2. Since the CO stretching bands can be identified without much ambiguity, attempts have been made to correlate their frequencies with the stability of the chelates3 or the ionization potential4 of various metals.