Über Oxoniccolate(II) der Alkalimetalle:K2NiO2, Rb2NiO2 und Cs2NiO2

On Oxoniccolates(II) of Alkali Metals: K₂NiO₂, Rb₂NiO₂, and Cs₂SiO₂. The hitherto unknown K₂NiO₂ (dichroic single crystals: redviolet/green, a=3.95₃, c=12.85₃ Å), Rb₂NiO₂ (analogous yellowred/green, a=4.17₄, c=13.18₆ Å) and Cs₂NiO₂ (analogous: darkgreen/green, a=4.41₃, c=13.59₀ Å) have been obtained, which surprisingly crystallize in the tetragonal Na₂HgO₂-type of structure with O–-Xi –-O]-dump-bells. The distance Ni –-O is very short: 1.68 Å. The K₂SiO₂-structure was determined using single crystal data, R=7.98% and R′=10.6% for 131 reflections hhl–- (h+3)hl. The magnetic datas for K₂NiO₂ and Cs₂NiO₂ obey the CURIE -WEISS -law (μ=3,0 μ_B. Θ ? ?30°K). The Madelung Part of Lattice Energy (MAPLE) is calculated and discussed.