Über neue Oxoniccolate: Zur Kenntnis von Na2[NiO2]

New Oxoniccolates: On the Knowledge of Na₂[NiO₂] The low temperature form of Na₂NiO₂, dark-red single crystals, obtained by heating Na₂O and ?NiO’? [Na:Ni = 2,2:1; 680°C, 3d, Ni cylinders] crystallizes orthorhombic with a = 2.82₀ b = 10.14₁ c = 8.28₃ Å, Z = 4 in the space group Cmc2₁. Due to fourcycle diffractometer data (290 hkl, MoKα, R = 2.8%) a new type of structure occurs, the NiO₂ part of which shows the PdCl₂ motive like in Li₂NiO₂. The coordination number of documentclass{article}pagestyle{empty}begin{document}$ mathop {rm N}limits^{rm 2}{rm a} $end{document} towards O is 4, of documentclass{article}pagestyle{empty}begin{document}$ mathop {rm N}limits^{rm 1}{rm a} $end{document} is 5. Effective Coordination Numbers, ECoN, and the Madelung Part of Lattice Energy, MAPLE, are discussed.