Three-dimensional iridium–germanium polyanions in the structures of Yb 2IrGe 2, LuIrGe, and Lu 3Ir 2Ge 3

Abstract

New germanides LuIrGe and Lu 3Ir 2Ge 3 were synthesized by arc-melting of the elements under an argon atmosphere and subsequent annealing slightly below the melting point in water-cooled silica tubes in a high-frequency furnace. Both compounds have been investigated by X-ray diffraction on powders and single crystals: TiNiSi type, Pnma, a=668.10(8), b=420.15(6), c=754.4(1) pm, wR 2=0.0913, 276 F 2 values, 19 variables for LuIrGe and Hf 3Ni 2Si 3 type, Cmcm, a=426.5(1), b=1019.1(2), c=1398.9(4) pm, wR 2=0.0751, 515 F 2 values, 28 variables for Lu 3Ir 2Ge 3. Yb 2IrGe 2 was obtained by reaction of the elements in a sealed tantalum tube in a water-cooled sample chamber of a high-frequency furnace. This germanide adopts the Zr 2CoSi 2 type, C2/ m, a=1027.1(8), b=422.8(2), c=1010.3(9) pm, β=116.64(9)°, wR 2=0.1067, 630 F 2 values, and 32 variables. Each germanide has one crystallographic iridium position with four germanium neighbours. The IrGe distances range from 246 to 268 pm. The strongly distorted IrGe 4 tetrahedra are connected only by IrGe bonds in LuIrGe, while additional GeGe bonds occur in Yb 2IrGe 2 (255 and 269 pm) and Lu 3Ir 2Ge 3 (268 pm). Together the iridium and germanium atoms built different three-dimensional [IrGe], [Ir 2Ge 3], and [IrGe 2] polyanions in which the rare earth atoms fill channels. The crystal chemical similarities of the three structures are discussed.