The synthesis of high surface area γ-Mo₂N materials using the nitridation of oxide precursors MoO₃, H₂MoO ₅ and H₂MoO₅·H₂O with ammonia at 650°C is described. H₂MoO₅ and its hydrated form were obtained from the reaction of MoO₃ and diluted H ₂O₂. The materials were characterized by means of X-ray powder diffraction, thermal analysis and nitrogen physisorption. Directly after the preparation, the nitride materials were subjected to different processing conditions: (1) contact to air, (2) inert gas or (3) treated with 1% O ₂(g)/N₂(g) gas mixture (Passivation). The synthesis and passivation conditions critically affect the specific surface area of the final product. By means of XRD a minor quantity of MoO₂ was detected in most of the products. The highest specific surface area of the nitrides was 158.4 m²/g for γ-Mo₂N materials using H ₂MoO₅·H₂O as the precursor. The high specific surface area corresponds to an average particle diameter of 4 nm, assuming a cubic morphology of the nanocrystals (d_p = 6/ρS _BET ρ = 9-5 g/cc). The nitrogen physisorption isotherms of γ-Mo₂N are of type IV, but pore sizes and diameters differ significantly depending on the synthesis conditions due to different defect structures of the intermediates generated in the course of the topotactic transformation of the oxides to nitrides.