Nitrides

Synthesis of Na₃N

One of the most pronounced violations of the homology principle in the periodic table is found in the binary nitrides of the alkali metals. While Li₃N forms spontaneously from the elements at room temperature, the synthesis of the homologues Na₃N and K₃N has failed so far in spite of a multitude of attempts during many decades. The synthesis of Na₃N succeeded via simultaneous deposition of sodium with activated nitrogen onto a sapphire substrate in the temperature range between 77 and 300 K. Na₃N crystallizes in the anti-ReO₃ structure type and decomposes already at 360 K to the elements.

Structure type: anti-ReO3 cubic, space group number 221 (PM-3M) Z=1, Na: (3d) N: (1a) a = 473.2 pm d(Na-N) = 236.6 pm Rp = 8.0 %, Rwp = 10.3 %

Rietveld refinement: blue (measurement), red (calculated), grey (difference) Line pattern: blue (Na3N), green: metallic sodium

Reference: D.Fischer, M. Jansen, Angew. Chem. 114 (2002) 1831-3; Angew. Chem. Int. Ed. 41 (2002) 1755-6.

Synthesis of K₃N

Two phases in the binary system K/N have been obtained via co-deposition of potassium and nitrogen at 77 K (subtrate temperature) and subsequent heating. The powder pattern of one of these phases can satisfactorily interpreted by assuming the composition K₃N and the anti-TiI₃ structure type, which is also adopted by Cs₃O.

Structure type: anti-TiI3 193 K, hexagonal, space group number 193 (P63/MCM) Z=2, K: (6g) N: (2b) a = 780 pm, c = 759 pm d(K-N) = 278 pm

Temperature dependent X-ray powder pattern of a K/N co-deposition. bottom to top: 77, 153, 173, 183......,273 K Line pattern metallic potassium

Reference: D.Fischer, Z.Cancarevic, J.C. Schön, M. Jansen, Z. Anorg. Allg. Chem. 630 (2004), 156-160.