CHEMISTRY OF INTERSTITIAL MOLYBDENUM TERNARY NITRIDES MNMO3N (M = FE,CO, N = 3, M = NI, N = 2)

Interstitial molybdenum ternary nitrides, MnMo3N (M = Fe and Co, n = 3 ; M = Ni, n = 2), can be obtained by ammonolysis of molybdate precurso rs, MMoO4. nH(2)O. A study of the influence of the preparative variabl es on the outcomes from this procedure is presented. Fe3Mo3N and Co3Mo 3N are prepared as nearly single phases at temperatures as low as 973 K, but higher temperatures are required to obtain pure samples (1073 a nd 1173 K for Fe and Co compounds, respectively). In the case of Fe3Mo 3N, moreover, a slow cooling of the samples results in segregation of impurities. The nickel nitride derivative shows a different stoichiome try, Ni2Mo3N, which results in the systematic presence of impurities. The structures of M3Mo3N (M = Fe, Co) have been refined from X-ray pow der diffraction data. These nitrides crystallize in the cubic system, space group Fd (3) over bar m [a = 11.076 33 (8) and 11.023 96(8) Angs trom for M = Fe and Co, respectively]. The structure of Ni2Mo3N has be en determined in an ab initio manner from X-ray powder diffraction dat a. The cell is cubic, space group P4(1)32 [a = 6.634 22(4) Angstrom]. Starting positional parameters were obtained by direct methods, and th e structure was refined by Rietveld analysis of the data. All three ni trides are prepared as phases constituted by submicrometer homogeneous particles. They show metallic behavior, and temperature programmed ox idation studies reveal an enhanced stability for the nickel derivative in an oxygen atmosphere.