Further Insight into Uranium and Thorium Metaphosphate Chemistry and the Effect of Nd3+ Incorporation into Uranium(IV) Metaphosphate

A tetragonal modification of uranium polymetaphosphate U(PO3)(4), a mixed U4+/Nd3+ polymetaphosphate ''(U0.62Nd0.38)(PO3)(4)'', and two new tetraphosphates, Th(P4O12) and U(P4O12), were synthesized. The structures of the obtained materials were characterized by X-ray diffraction and Raman spectroscopy. The presence of Nd in (U0.62Nd0.38)(PO3)(4) was proven by energy-dispersive X-ray spectroscopy (EDX), and the measured degree of substitution for U agrees well with the X-ray crystallography results; however, the mechanism of the necessary charge compensation could not be identified. The cation arrangements in the crystal structures of thorium and uranium polymetaphosphates have been studied in terms of Voronoi-Dirichlet polyhedra. Different conformations of the tetraphosphate polyanions were observed in the crystal structures of Th(P4O12) and U(P4O12). The Raman spectrum of a single crystal of Th(P4O12) was recorded, and the bands were assigned.