Chemical and spectroscopic studies in metal β-diketonates. VIII. Electronic spectral studies on some trivalent 3d metal diketonates and their γ-substituted derivatives

Abstract

Electronic absorption spectra of solutions of chromium(III), iron(III), and cobalt(III) β-diketonates have been measured in the 200- 1200mμ region. Detailed interpretation of the spectral data are provided in terms of the πg → π4, the electron transfer (d_ε → π₄), and the ligand field (d → d*) transitions of the various components. The effects of γ-substituents on the chelate rings upon the positions of different transitions are discussed. Substitution of a halogen results in bathochromic shift in π₃ → π₄, d_ε → π₄, and d → d* transitions of each chelate, presumably due to extension of conjugation, interaction among d_ε and π₃ orbitals (which raises d_ε orbitals to a higher energy), and decrease in ligand field effect respectively. The hypsochromic shifts observed in the cases of NO₂, SCN, Ac, and CHO γ-substituents are perhaps due to the steric inhibition of resonance with the chelate ring.