Abstract

Recently, Toivonen and Niinisto reported that UO₂SO₄·(urea)₂ is capable of existing in two crystalline forms. The structures of these are very similar, with the uranium atom lying at the center of a pentagonal bipyramid formed by oxygen atoms. Of the five equatorial oxygens, three belong to sulfate groups and two to urea molecules: The bridging tridentate sulfate groups (labeled as 3,4,5) join the bipyramids into infinite double chains, and the α and β polymorphs differ in how these chains are packed.

© 1984 Optical Society of America