Dicalcium nitride, Ca₂N - A 2D 'excess electron' compound; synthetic rotates 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 R3̄m (a = 3.62872(3) Å, c = 19.0921 (4) Å, V = 217.72(1) ų, Z = 3, c/a = 5.26). INCa₂]⁺ 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.