Neutron diffraction study of uranyl oxalate [UO2(C2O4)(D2O)] · 2D2O

A powdered sample of uranyl oxalate [UO2(C2O4)(D2O)] · 2D2O (compound I) is studied using neutron diffraction. The crystals are monoclinic, space group P21/c, with a = 5.608(1) Å, b = 17.016(3) Å, c = 9.410(2) Å, β = 98.9369(2)°, Z = 4, Rf = 0.042, RI = 0.054, x2 = 1.5. The main structural units of the crystals are [UO2(C2O4)(D2O)] chains. These chains, which belong to the AK02M1 (A = UO22+) crystal-chemical group of the uranyl complexes, lie parallel to [101]. The water molecules in the crystals of I are hydrogen-bonded into zigzag chains running along [100]. Since each third oxygen atom of the chain formed of water molecules is coordinated to the uranium atom, the uranyl oxalate chains are linked into {[UO2(C2O4)(D2O)] · 2D2O} layers that lie normal to [010]. The layers are linked into the framework through interlayer hydrogen bonds (D2O)O-D···O (oxalate).