Zur Kristallchemie von Oxoniccolaten der Alkali‐, Erdalkali‐ und Seltenerdmetalle

Abstract

AbstractThis review describes features of the crystal chemistry of oxoniccolates containing large cations like alkali‐, alkaline earth and rare earth metals. Starting with alkali‐oxoniccolates it is shown that Ni+ exhibits the unusual coordination number CN = 2 (dumbbells) in K2/ Rb2/ Na2NiO2 and K3NiO2. K2NiO2 is the only known oxoniccolat showing O–Ni–O‐dumbbells with nickel in the oxidation state Ni2+. The trigonal planar coordination (found within silver‐oxocompounds) is restricted to Ba3NiO4 and K9Ni2O7. Square planar polygons (NiO4) are found in Nd4Ni3O8; Na2NiO2; Ki2NiO2; BaNiO2 and SrNiO2 for example. A special quality in the crystal chemistry of connected square planar NiO4‐polygons is the formation of Ni6O12‐rings in Ba2NaNi3O6. There are two compounds showing Ni3+O4‐tetrahedra: K9Ni2O7 and Na5NiO4. All the other oxoniccolates exhibit octahedral or trigonal prismatic coordination of nickel by oxygen. Always of interest are the so called one dimensional oxides, showing chains of two times face‐shared octahedra and/or trigonal prisms, found in Sr3Yb0.89NiO6, Sr3PbNiO6; Sr12Ni7.5O27; Sr4Ni3O9; BaNi0.83O2.5 and NaSr12Ni7O23. Large chains of the type –[(octahedron)2–(prism)–(octahedron)2–prism–(octahedron)3–(prism)–(octahedron)2–(prism)–(octahedron)2]– filled by Ni3+ and Ni4+ are found in Sr9Ni6.64O21. Many of the oxidation states of nickel are published with non integral valence states like Ni2.667+, Ni2.5+, Ni2.292+, Ni3.614. Using calculations of the Coulomb‐terms of lattice energy most of the mixed valences could be split up in integral numbers protecting the electro neutrality between metal ions and oxygen.