CRYSTAL STRUCTURE OF DICALCIUM NITRIDE

The structure of a nitride of the stoichiometry Ca2N has been determined from single-crystal X-ray data. Dicalcium nitride is rhombohedral with unit-cell dimensions a = 6.603 Å, α = 31° 59′, Dm = 2.17 g cm-3, Z = 1, Dc, = 2.18 g cm-3, the space group being [formula omitted]. Full-matrix least-squares refinement has reached R = 0.13 for 71 visually estimated reflections. Ca2N has a layer structure of the anti-CdCl2 type. The layers are widely separated, their closest approach being a Ca-Ca distance of 4.35 Å, much larger than those in the metal. The nitrogen atoms lie at centers of symmetry, within the layers, and have distorted octahedral coordination. The electrical properties of Ca2N are discussed in relationship to the structure and with reference to other M2X compounds. © 1968, American Chemical Society. All rights reserved.