Heavy atom effect in diamagnetic metal acetylacetonates

Abstract

Spectral data are presented for acetylacetonate complexes of eighteen diamagnetic closed shell metal ions. The nature of the metal ion has relatively little effect on the absorption and phosphorescence energies, but has a very marked effect on the phosphorescence lifetime, τ, in solid ethanol glasses at 77 K. The possibility that the observed variations in τ are the result of an intramolecular heavy atom effect is examined. Comparison of τ with ligand ¹H n.m.r. resonances indicate that a significant degree of heavy atom induced spin–orbit coupling occurs only with the Th⁴⁺, Lu³⁺, La³⁺ and In³⁺ complexes. In the other cases it is suggested that the principal factor in determining τ may be the energy difference between the T_π,π^* and T_n,π^* states and a specific model is proposed.