[en] Structural and magnetic properties of the GdFe_12-xMo_x compounds having the ThMn₁₂ type of structure were studied. Rare-earth nitrides of the composition GdFe_12-xMo_xN_y were prepared by the reaction of GdFe_12-xMo_x with nitrogen gas at 475 C. The crystal structure and lattice constants have been determined for all compounds. The lattice expansion of the nitrogenated compounds is mainly along the a-axis, the Curie temperatures are increased by about 110 K. We investigated the effect of interstitial nitrogen on the magnetic properties and the ¹⁵⁵Gd Moessbauer spectrum of GdFe_12-xMo_x. Values of the electric field gradient V_zz derived from the quadrupole splitting of the spectra were strongly negative, with V_zz=-21.3x10²¹ V m^-2 and V_zz=-19.9x10²¹ V m^-2 for x=1.5 and 3.0, respectively. Nitrogenation is shown to lead to a sign reversal of the 4f as well as of the 3d sublattice anisotropies. ((orig.))