Two Hexagonal Series of Lanthanoid(III) Oxide Fluoride Selenides: M6O2F8Se3 (M: La—Nd) and M2OF2Se (M: Nd, Sm, Gd—Ho).

The two series of title compounds are prepared from mixtures of MF3 (M: La—Nd, Sm, Gd—Ho), M2O3, M, and Se using excess CsI as a flux (Nb tubes, 850 °C, 10 d).