The first uranyl complexes with valerate ions

FT–IR spectroscopy and single-crystal X-ray structure analysis were used to characterize the discrete neutral compound di­aqua­dioxidobis(n-valerato-κ²O,O′)uranium(VI), [UO₂(C₄H₉COO)₂(H₂O)₂], (I), and the ionic compound potassium dioxidotris(n-valerato-κ²O,O′)uranium(VI), K[UO₂(C₄H₉COO)₃], (II). The U^VI cation in neutral (I) is at a site of 2/m symmetry. Potassium salt (II) has two U centres and two K⁺ cations residing on twofold axes, while a third independent formula unit is on a general position. The ligands in both compounds were found to suffer severe disorder. The FT–IR spectroscopic results agree with the X-ray data. The composition and structure of the ionic potassium uranyl valerate are similar to those of previously reported potassium uranyl complexes with acetate, propionate and butyrate ligands. Progressive lengthening of the alkyl groups in these otherwise similar compounds was found to have an impact on their structures, including on the number of independent U and K⁺ sites, on the coordination modes of some of the K⁺ centres and on the minimum distances between U atoms. The evolution of the KUO₆ frameworks in the four homologous compounds is analysed in detail, revealing a new example of three-dimensional topological isomerism in coordination com­pounds of U^VI.