Dicalcium nitride, Ca2N -: a 2D "excess electron" compound;: synthetic routes and crystal chemistry

The subnitride Ca2N has been prepared via several synthetic routes described for the first time, including reduction of Ca3N2 and reaction of Ca metal dissolved in liquid sodium with nitrogen gas. Products have been characterised by powder X-ray and powder neutron diffraction. Crystallite morphology and compound stoichiometry have been examined by SEM/EDAX. Ca2N crystallises with a hexagonal layered structure in space group <R(3)over bar>m (a = 3.62872(3) Angstrom, c = 19.0921(4) Angstrom, V = 217.72(1) Angstrom(3), Z = 3, c/a = 5.26). [NCa2](+) layers composed of compressed, edge-sharing NCa6 octahedra stack along the c-axis and are separated by large "van der Waals" gaps. The material is metallic and paramagnetic at room temperature. The c-parameter, [NCa2](+) layer thickness and interlayer gap are larger than previously reported and there is no evidence of hydride or other anion intercalation between layers.