LICU2O2 AND LICU3O3 - NEW MIXED VALENT COPPER OXIDES

Black, shiny crystals of LiCu2O2 (I) and LiCu3O3 (II) were prepared by melting a mixture of Li2CO3 and CuO (1:4) in a corundum crucible at 1150°C (I) or heating a mixture of Li2CO3 and CuO (1:5) in a corundum crucible at 825°C (II). Crystals of (I) had tetragonal symmetry and the structure was solved in P42 nmc with a = 571.9(1), c = 1240.1 (4) pm, and Z = 8 (four-circle diffractometer CAD4, 201 I0(hkl), MoKα, RW = 3.1%). Nearly identical but orthorhombic crystals (I′) could be isolated from a different batch ((I′): a = 571.4(3), b = 572.7(3), c = 1241.0(4)pm). The crystal structure of (II) was solved and refined in P4 mmm with a = 0281.0(1), c = 888.9(4) pm, and Z = 1 (four-circle diffractometer CAD4, 82 I0(hkl), MoKα, RW = 1.9%). Characteristic building units in (I) and (II) are CuIO2-dumbbells (dCuO = 185 pm, LiO5-pyramids, and CuIIO4-squares with one or two additional O atoms at about 242-259 pm. In (I) the CuIIO4-squares (dCuO = 198 pm (4x)) are connected edge-shared to form infinite chains. The square-pyramidally surrounded Li atoms also form chains which, together with the CuIIO-chains, form double sheets separated by the CuO2-dumbbells. In the orthorhombic crystal (I′) Li and CuII are partially disordered. In (II) Li and CuII are completely disordered on centers of 44 nets of O atoms (dCuO = 199 pm (4x)). Three sheets are packed in such a way that the coordination spheres of CuII or Li are completed by additional O atoms to form square pyramids (dCuO = 242 pm) or elongated octahedra (dCuO = 259 pm (2x)). A triple sheet of this type is connected via CuIO2-dumbbells (dCuO = 185 pm) to form a three-dimensional framework. (I) is an insulator and antiferromagnet (Néel temperature 40 K). At higher temperature it obeys the Curie-Weiss law with μeff = 1.93 μB Cu atom and Θ = -75 K; (II) is a paramagnetic semiconductor with ρ{variant} = 0.1 Ω · cm, μeff = 1.83 μB Cu2 formula unit at 293 K; this is about half of the moment one would expect for two CuII atoms. © 1990.