Expanding the Crystal Chemistry of Uranyl Peroxides: Four Hybrid Uranyl-Peroxide Structures Containing EDTA

The first four uranyl peroxide compounds containing ethylenediaminetetra-acetate (EDTA) were synthesized and characterized from aqueous uranyl peroxide nitrate solutions with a pH range of 5–7. Raman spectra demonstrated that reaction solutions that crystallized [NaK₁₅[(UO₂)₈­(O₂)₈(C₁₀H₁₂O₁₀N₂)₂­(C₂O₄)₄]­·(H₂O)₁₄] (<b>1</b>) and [Li₄K₆[(UO₂)₈­(O₂)₆(C₁₀H₁₂O₁₀N₂)₂­(NO₃)₆]­·(H₂O)₂₆] (<b>2</b>) contained excess peroxide, and their structures contained oxidized ethylenediaminetetraacetate, EDTAO₂^4–. The solutions from which [K₄[(UO₂)₄­(O₂)₂(C₁₀H₁₃O₈N₂)₂­(IO₃)₂]­·(H₂O)₁₆] (<b>3</b>) and LiK₃[(UO₂)₄(O₂)₂­(C₁₀H₁₂O₈N₂)₂­(H₂O)₂]­·(H₂O)₁₈ (<b>4</b>) crystallized contained no free peroxide, and the structures incorporated intact EDTA^4–. In contrast to the large family of uranyl peroxide cage clusters, coordination of uranyl peroxide units in <b>1</b>–<b>4</b> by EDTA^4– or EDTAO₂^4– results in isolated tetramers or dimers of uranyl ions that are bridged by bidentate peroxide groups. Two tetramers are bridged by EDTAO₂^4– to form octamers in <b>1</b> and <b>2</b>, and dimers of uranyl polyhedra are linked through iodate groups in <b>3</b> and EDTA^4– in <b>4</b>, forming chains in both cases. In each structure the U–O₂–U dihedral angle is strongly bent, at ∼140°, consistent with the configuration of this linkage in cage clusters and other recently reported uranyl peroxides