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] (1) and [Li4K6[(UO2)8­(O2)6(C10H12O10N2)2­(NO3)6]­·(H2O)26] (2) contained excess peroxide, and their structures contained
oxidized ethylenediaminetetraacetate, EDTAO24–. The solutions from which [K4[(UO2)4­(O2)2(C10H13O8N2)2­(IO3)2]­·(H2O)16] (3) and
LiK3[(UO2)4(O2)2­(C10H12O8N2)2­(H2O)2]­·(H2O)18 (4) crystallized contained no free peroxide,
and the structures incorporated intact EDTA4–. In
contrast to the large family of uranyl peroxide cage clusters, coordination
of uranyl peroxide units in 1–4 by
EDTA4– or EDTAO24– results
in isolated tetramers or dimers of uranyl ions that are bridged by
bidentate peroxide groups. Two tetramers are bridged by EDTAO24– to form octamers in 1 and 2, and dimers of uranyl polyhedra are linked through iodate
groups in 3 and EDTA4– in 4, 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.