Complexation of tetravalent uranium cations by the As4W40O140 cryptand

Abstract

The complexation properties of the anionic [As₄W₄₀O₁₄₀]²⁸⁻ macrocycle were studied towards the trapping of the 5f tetravalent uranium tetrachloride precursor. In aqueous solution, the increase of the uranium concentration (from one to six molar equivalents per [As₄W₄₀O₁₄₀] unit) leads to the crystallization of three new isolated crystalline compounds, [{U₂(μ²-OH)₃(μ²-O)}AsW₄₀O₁₄₀]²⁵⁻ (1), [{U₂(μ²-O)(HCOO)₃}As₄W₄₀O₁₄₀]²⁵⁻ (2) and [{U₄(μ²-O)₂(HCOO)₄}As₄W₄₀O₁₄₀]²⁰⁻ (3), in which two to four uranium atoms were trapped within the cryptand-like molecule. In compounds 1 and 3, the macrocycle keeps its architecture, while a rotation of the position of one {AsW₉O₃₃} sub-unit of the cryptand could be observed in compound 2. All the inclusion complexes have been characterized by single-crystal X-ray diffraction, IR spectroscopy, TGA, SEM/EDX microscopy, SAXS and ICP analyses.