Crystal data for the monohydrated uranyl bis(dihydrogen phosphate), UO 2 (H 2 PO 4 ) 2 .H 2 O, and uranyl bis(dihydrogen arsenate), UO 2 (H 2 AsO 4 ) 2 .H 2 O

Guinier patterns of UO 2 (H 2 PO 4 ) 2 .H 2 O and UO 2 (H 2 AsO 4 ) 2 .H 2 O have been indexed. They both have space group Cc or C 2/ c . The cell constants are, for the phosphorous compound: a = 12.892(2), b = 8.745(2) and c = 8.906(2) Å, β = 123.94(2)°, U = 833.0(2) Å 3 , D m = 3.48(1), D c = 3.842 Mg m −3 , Z = 4; for the arsenic compound: a = 13.156(2), b = 8.853(1) and c = 9.046(2) Å, β = 124.54(2)°, U = 867.9(2) Å 3 , D c = 4.361 Mg m −3 , Z = 4. Indexed powder data are given.