The effects of hydrofluoric acid addition on the hydrothermal synthesis of templated uranium sulfates

Abstract

The effect of employing hydrofluoric acid as a mineraliser in the formation of organically templated uranium sulfate materials has been studied. Variable amounts of HF_(aq) were added to a series of reaction gels in which all other reactant concentrations were invariant, resulting in the formation of three different phases, depending upon the fluoride concentration. Two of these phases are novel; [N₂C₄H₁₄][UO₂(H₂O)(SO₄)₂] is a new templated uranium sulfate, containing anionic [UO₂(H₂O)(SO₄)₂]²⁻ chains that hydrogen bond to one-another forming pseudo-layers, and [N₂C₄H₁₄][UO₂F(SO₄)]₂ is the first example of a templated uranium sulfate fluoride, which consists of uranium fluoride chains linked by sulfate groups to form [UO₂F(SO₄)]⁻ layers. The role of F⁻ in these reactions is two-fold; it acts as a mineraliser when present in small concentrations, while it is incorporated into the reaction product when present in larger mole fractions. Both of the new materials have been characterised using a range of physical techniques including single crystal X-ray structure analysis.