SYNTHESIS AND STRUCTURAL INVESTIGATION OF A NEW TERNARY TRANSITION-METAL NITRIDE, CO3W3N

A new ternary transition metal nitride, Co3W3N, has been synthesized b y the ammonolysis of a chemically derived metalloorganic precursor. Th e compound crystallizes in the eta-carbide structure which is cubic in the space group Fd (3) over bar m (227) with Z=16, as determined from powder X-ray diffraction and Rietveld refinement of the resulting dif fraction pattern. The refinement converged with R-wp =0.1198, R-p=0.07 25, R-I=0.0400, and S=1.63. The unit cell of Co3W3N has a lattice para meter of a=11.0995(2) Angstrom. The compound is isostructural with Co3 W3C, the ideal structure consisting of eight regular octahedra of tung sten atoms centred on a diamond cubic lattice and eight regular tetrah edra of cobalt atoms centred on a second diamond cubic lattice that in terpenetrates the first through a 1/2,1/2,1/2 unit cell translation. S ixteen additional cobalt atoms are tetrahedrally coordinated around th e cobalt tetrahedra and sixteen nitrogen atoms surround the tungsten o ctahedra in tetrahedral coordination. (C) 1998 Elsevier Science S.A.