Uranyl Ion Coordination.

A review of the known crystal structures containing the uranyl ion shows that plane-pentagon coordination is equally as prevalent as planesquare or plane-hexagon. It is suggested that puckered-hexagon configurations of OH(-) or H(2)O about the uranyl group will tend to revert to plane-pentagon coordination. The concept oft of pentagonal coordination is invoked for possible explanations of the complex crystallography of the natural tiranyl hydroxides and the unusual behavior of polynuclear ions in hydrolyzed uranyl solutions.