Structural Evolution in the Rare-Earth Uranyl Vanadates Ln2[(UO2)2V2O8]3·nH2O, Singularity of the Lanthanum Compound, and Single-Crystal to Single-Crystal Partial Dehydration

Abstract

A family of compounds with general chemical formula Ln2[(UO2)2V2O8]3·nH2O, where Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Er, Yb, Y has been hydrothermally synthesized and structurally characterized. The structures of all these compounds can be described as the stacking of carnotite-type uranyl vanadate layers pillared by lanthanide–oxygen polyhedra. Except for La, they are isostructural, and the crystal structure determination of Nd2[(UO2)2V2O8]3·22H2O and Y2[(UO2)2V2O8]3·20H2O shows that the ud/du/du geometrical isomers of the uranyl vanadate layers are pillared by Nd(Oyl)2(H2O)7 and Y(Oyl)2(H2O)6 polyhedra, respectively, through interactions between the lanthanide ion and the oxygens Oyl of two vanadyl ions forming V═Oyl–Ln–Oyl═V entities. In the La compound, the ud/du geometrical isomers of the uranyl vanadate layers are pillared by La(Oyl)2(H2O)8, through interactions between the lanthanum ion and the oxygens Oyl of one vanadyl and one uranyl ion, forming U═Oyl–La–Oyl═V entities. Thermogravimetric and high-t...