Discovery of Cs2(UO2)Al2O5 by Molten Flux Methods: A Uranium Aluminate Containing Solely Aluminate Tetrahedra as the Secondary Building Unit.

The flux synthesis, solid state synthesis, and characterization of a new aluminate, Cs2(UO2)Al2O5, are reported. Cs2(UO2)Al2O5 crystallizes in the tetragonal space group I41/ amd with lattice parameters a = 7.3254(2) and c = 30.9849(7) and is constructed from edge-sharing chains of UO7 pentagonal bipyramids that are connected to [Al2O5]4- two-dimensional sheets. The cesium cations, which are heavily disordered, occupy small channels in the a and b directions in the framework structure. The optical properties and ion exchange behaviors are reported along with DFT calculations that support the observed results of the ion exchange experiments.