Ein sauerstoffreiches Neodymcuprat: Hochdrucksynthese und Kristallstruktur von Nd12Cu6O25 („Nd2CuO4,17”︁)

An Oxygen-rich Neodymium Cuprate: High-pressure Synthesis and Crystal Structure of Nd₁₂Cu₆O₂₅ (“Nd₂CuO_4.17”) Single crystals of Nd₁₂Cu₆O₂₅ (“Nd₂CuO_4.17”) could be obtained by reaction of Nd₂O₃ und CuO with KO₂ in a modified Belt-type apparatus at 40 kbar, 1500°C. The compound crystallizes in the monoclinic space group C2/m with a = 17.128(6), b = 3.7288(6), c = 18.364(6) Å, β = 111.22(1)º and Z = 2. The structure refinement converged at R1 = 0.0302 for 1451 reflections with F_o > 4σ(F_o) and R1 = 0.0903, wR2 = 0.0767 for all 2571 data. The structure-determining feature are Cu(1,2)? O octahedral chains, interrupted by Cu(3) atoms in square-planar coordination. Each of this CuO₄ groups is connected to another one, resulting in short copper-copper distances (d_{Cu? Cu} = 3.012 Å). A comparison of the structure of “Nd₂CuO_4.17” with those of La₂CuO₄ and Nd₂CuO₄ makes the structural relations of the former with La₂CuO₄ and, hence, the aristotype K₂NiF₄ evident, in spite of the close stoichiometric similarity between Nd₂CuO₄ and “Nd₂CuO_4.17”.