Redetermination of the crystal structure of barium uranate

Barium uranate, BaUO4, crystallizes in the centro-symmetric orthorhombic space group, Pbcm (D2h11; No. 57) with a = 5.744(3), b = 8.136(4), c = 8.237(3) A for M = 439.36 and Z = 4. X-ray diffraction data complete to 2θ = 60° (Mo Kα radiation) were collected using a G.E. XRD-490 automated diffractometer. The structure was solved by a combination of Patterson, Fourier and least-squares techniques. The final discrepancy indices are RF = 0.059 and wRF = 0.107 for 507 reflections where F0 > σ (F0). Distinct primary U-O bonds and polymeric secondary U-O bonds form a distorted octahedral U(VI) coordination sphere where the U-O bond distances are shown to be highly influenced by the Ba2+ ion. The apical primary uranium-oxygen bond length is 1.872(12) A while the basal secondary U-O bond distances are 2.196(6) and 2.223(6) A.