Nb5N6−δOyand Ta5N6−δOyhave been synthesized by reacting iron-containing precursors (FeMO4, FeM2O6, Fe2O3/M2O5, or FeM,M− Ta, Nb) with flowing ammonia at 700 and 900°C for the niobium- and tantalum-containing precursors, respectively. It is observed that the oxynitride materials may be synthesized at these temperatures only by using precursors that contain iron. The structures of these materials, which were determined by Rietveld refinement of powder X-ray diffraction data, show marked similarity to the structures of several ternary nitrides synthesized by similar methods. The role of iron in the formation of these materials is discussed.