EFFECT OF COMPLEXATION ON THE EXCITED-STATE OF URANYL BETA-DIKETONATO COMPLEXES - APPLICATION OF THE ENERGY-GAP LAW

Excited-state properties of four series of dioxouranium(vi) (uranyl) beta-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)2L and UO2L5(ClO4)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)2thf 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 nu3 (asymmetric vibration) of U = O in uranyl ion, were obtained. The energy gap law accounts for E(o,o) being the major perturbing factor of the lifetimes.