Positron lifetime diagnostics of β-diketonates of bivalent metals

Positron lifetime diagnostics was used to study manganese(II), cobalt(II), nickel(II), copper(II), and zinc(II) acetylacetonates, γ-chloro and γ-bromo chelate complexes of cobalt and nickel, and similar halo and nitro chelate complexes of copper. The dependences of the annihilation lifetime τ₂ on the metal nature and the stability constant of the metal chelate ring were established. The annihilation lifetime and intensity were found to depend not only on the electronic effect of the γ-substituent in the chelate ring but also on the structure of the complex. A comparison of the dependences of the frequencies of the C-O and M-O stretching vibrations on τ₂ revealed that a positron interacts simultaneously with the γ-carbon atoms and the O atoms of the chelate ring, whose accessibilities are determined by the structures of bis(chelates). The plots of the ionization potentials of the n-orbitals of the bis(chelates) vs. τ₂ were similar to the plots of the quenching rate constant of the benzophenone triplet vs. τ₂ in the presence of the bis(chelates).