Spectral Investigations of Metal Complexes of β-Diketones. I. Nuclear Magnetic Resonance and Ultraviolet Spectra of Acetylacetonates1

A report of proton resonance and ultraviolet spectra of a broad range of metal ion complexes of acetylacetone is presented. The n.m.r. spectra of diamagnetic complexes provide no support for the postulate of benzenoid resonance in the chelate rings, as has been suggested by Calvin nor are any great differences in electron density at the unique carbon atom in the ring indicated. Definitive ultraviolet spectra of thirty acetylacetone complexes are reported. All of these data in general and particularly in certain comparisons indicate that the electrostatic model of Beiford, et al., cannot account for the variation in energy of the presumed pi - pi /sup */ transition. The energy of this transition cannot be correlated with any simple parameter of the complexed metal ion, and it is believed that it is determined by several such parameters, among which is the ability of the metal ion to participate in d pi -p pi overlap with the pi system of the chelate ring.