Spectroscopic properties of K5Li2UF10

A new uranium (III) fluoro-complex of the formula K5Li2UF10 has been synthesised and characterised by X-ray powder diffraction and electronic absorption spectra measurements. The compound crystallises in the orthorhombic system, space group Pnma, with a = 20.723, b = 7.809, c = 6.932 A, V = 1121.89 A3, Z = 4 and is isostructural with its K5Li2NdF10 and K5Li2LaF10 analogous. The absorption spectrum of a polycrystalline sample of K5Li2UF10 was recorded at 4.2 K in the 3500-45,000 cm-1 range and is discussed. The observed crystal-field levels were assigned and fitted to parameters of the simplified angular overlap model (AOM) and next to those of a semi-empirical Hamiltonian, which was representing the combined atomic and one-electron crystal-field interactions. The starting values of the AOM parameters were obtained from ab initio calculations. The analysis of the spectra enabled the assignment of 71 crystal-field levels of U3+ with a relatively small r.m.s. deviation of 37 cm-1. The total splitting of 714 cm-1 was calculated for the 4I9/2 ground multiplet