Effect of complexation on the excited state of uranyl β-diketonato complexes: applications of the energy gap law

Abstract

Excited-state properties of four series of dioxouranium(VI)(uranyl)β-diketonato complexes UO₂(L–L)₂thf, UO₂(L–L)₂ dmso [L–L = acac (acetylacetonate), tfacac (trifluoroacetylacetonate), hfacac (hexafluoroacetylacetonate), btfa (benzoyltrifluoroacetylacetonate), ba (benzoylacetylacetonate), dbm (dibenzoylmethanide) and tta (tenoyltrifluoroacetylacetonate); thf = tetrahydrofuran, dmso = dimethyl sulfoxide], UO₂(acac)₂ L and UO₂L₅(CIO₄)₂[L = dmso, dma (N,N-dimethylacetamide), hmpa (hexamethylphosphoric triamide), dmf (N,N-dimethylformamide) and tmp (trimethyl phosphate)] have been studied at 296 and 77 K. The lifetimes of the excited states of UO₂(L–L)₂ thf were first measured at ambient temperatures in the liquid solvent and range from 0. 90 ns for L–L = acac and ba, to 484 ns for L–L = hfacac, Good correlations between E_o,o(0′–0″ band energies in the first electronic transition) and the lifetimes of the excited states, and also between E_o,o and ν₃(asymmetric vibration) of UO in uranyl ion, were obtained. The energy gap law accounts for E_o,o being the major perturbing factor of the lifetimes.