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The Soret effect in nonstoichiometric copper(I)-oxide (cuprite, Cu 2Àd O) has been studied experimentally by means of non-isothermal solid state galvanic cells (thermocells) under different boundary conditions. At high temperatures and high oxygen activities, copper metal migrates down the temperature gradient and a gradient in the nonstoichiometry is established under stationary conditions. The heat of transport of copper metal is determined as Q* Cu c180 kJ/mol at a temperature of 1000 8C and at an oxygen activity of log a O 2 =À2.95. This result agrees with recent theoretical simulations of the heat of transport of atoms migrating via a vacancy mechanism. These predict a positive sign of the heat of transport and a considerably larger value than the activation energy for the atomic jumps. D

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CuDy 2 [B 8 O 16 ] and CuHo 2 [B 8 O 16 ]: Two New "Metaborates" with a ∞ 1 [B 8 O 16 ] 8− Anion. -Single crystals of the title compounds CuDy 2 [B 8 O 16 ] (IVa) and CuHo 2 [B 8 O 16 ] (IVb) are obtained by annealing the element oxides at 1030-1060 • C. Compound (IVa) appears to be isotypic to the monoclinic crystal structure of CuTb 2 [B 8 O 16 ], while compound (IVb) represents an orthorhombic variant. Single crystal X-ray studies reveal space group P2 1 /c with Z = 2 for (IVa) and Pbam, Z = 2 for (IVb). The structures contain 1 [B 8 O 16 ] 8− chains isolated from each other, which include tri-and tetracoordinated boron. The chains consist of alternating 12-and 8-membered rings of boron and oxygen atoms connected by BO 4 units. -(WIESCH, A.; TIMM, H.; BLUHM, K.

Nearly colourless single crystals of the compounds CuDy2 [B80 i 6] (I) and CuHo2[B80 )6] (II) have been obtained by a B20 3 flux technique. They crystallize in the structure of CuTb2 [B80 )6] (I) or in an orthorhombic variant (II). X-ray investigations on single crystals led to the space group C2h -P2!/c (Nr. 14) with lattice parameters a = 1025,5(10); b = 836,99(10); c = 621,2(8) pm, ß = 90.47(10)°; Z = 2 (I) and D^h -Pbam (Nr. 55) with a = 840,7(2), b = 616,6(2), c = 1022,0(2) pm, Z = 2 (II). The structures contain 1 [B80 16]8_ chains isolated from each other, which include tri-and tetracoordinated boron, T'fie chains consist of alternating twelve and eight-membered rings of boron and oxygen atoms connected by B 0 4 units. Dy,+ and H o 3+ are octacoordinated and Cu2+ is hexacoordinated in elongated octahedra by oxygen. The relation between these two structures is discussed. Einleitung