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The intermetallic compounds CaCuGe, CaAuIn, and CaAuSn can be prepared from the elements in sealed tantalum tubes or in glassy carbon crucibles in a high‐frequency furnace. Their crystal structures were determined from single crystal X‐ray data. The three compounds crystallize with the same subcell structure (KHg2), however, they form three clearly perceptible superstructures with different unit cells, but all in space groups Pnma: a = 2124.9(6) pm, b = 436.0(2) pm, c = 749.4(5) pm, Z = 12, wR2 = 0.0789, 1303 F2 values, 56 variables for CaCuGe (own structure type), a = 738.2(1) pm, b = 459.4(1) pm, c = 839.4(2) pm, Z = 4, wR2 = 0.0651, 656 F2 values, 20 variables for CaAuIn (TiNiSi type), a = 3690.3(3) pm, b = 470.5(1) pm, c = 813.6(2) pm, Z = 20, wR2 = 0.1294, 1730 F2 values, 92 variables for CaAuSn (new structure type). The three structures may be considered as superstructures of the KHg2 type with an ordered arrangement of the transition metal and germanium (indium, tin) atoms on the mercury position. Each calcium atom in the structures of CaCuGe, CaAuIn, and CaAuSn has an distinctly ordered near‐neighbor environment of six transition metal (T) and six p element (X) atoms in the form of two counter‐tilted T3X3 hexagons. All known superstructures of the KHg2 type are described in terms of a group‐subgroup scheme.

Intermetallic Calcium Compounds, Crystal Structure, Mössbauer Spectroscopy, Chemical Bonding New stannides CaTSm (T = Rh, Pd, Ir) and Ca2P hSn5 were prepared as single phase materials by a reaction o f the elements in glassy carbon crucibles under flowing purified argon. The four compounds were investigated by X-ray diffraction both on powders and single crystals and their structures were refined from single crystal data. The stannides CaTSn2 (T = Rh, Pd, Ir) adopt the M gC uA l, structure with space group Cmcm: a = 434.1(1), b = 1081.7(3), c = 748.8(2) pm, wR2 = 0.040Ö, 451 F2 values for C aRhSn,, a = 442.7(2), b = 1113.8(4), c = 745.6(2) pm, wR2 = 0.0318, 471 F ; values for CaPdSn2, and a = 429.5(1), b = 1079.5(3), c = 758.6(2) pm, wR2 = 0.0465, 455 F2 values for CaIrSn2 with 16 variables for each refinement. Chemical bonding analysis leads to the description o f a distorted filled CaSni substructure in which the tin-tin bonding is modified by the insertion o f transition metal atoms into the planar calcium layers, favoring strong tin-transition metal bonding. ll9Sn Mössbauer spectra show single signals for CaTSn2 (T = Rh, Pd, Ir) which are subjected to quadrupole splitting. The electron count o f the CaTSn2 compounds correlates with the ll9Sn isomer shift. Ca^PtiSns crystallizes with the Y b2Pt3Sn5 type structure: Pnma, a = 734.8(1), b = 445.50(7), c = 2634.8(5) pm, wR2 = 0.0636, 1406 F" values and 62 variables. The platinum and tin atoms in Ca2Pt3Sns build a com plex three-dimensional [Pt^Sns ] polyanion in which the calcium cations fill distorted pentagonal and hexagonal channels. According to semi-empirical band structure calculations the strongest bonding interactions are found for the Pt-Sn contacts, follow ed by Sn-Sn bonding. The ll9Sn M össbauer spectrum o f Ca2Pt3Sn5 shows two superimposed signals at 6 = 2.10(3) and 6 -2.18(6) mm/s.

-014Structure and Properties of the Stannide Eu 2 Au 2 Sn 5 , and Its Relationship with the Family of BaAl 4 -Related Structures.-The title compound Eu 2 Au 2 Sn 5 , prepared by arc melting of the elements, crystallizes in a new structure type, space group P2 1 /m, which can be considered as an ordered defect variant of the BaAl 4 type. The Au and Sn atoms form a complex three-dimensional [Au 2 Sn 5 ] substructure with short Au-Sn and Sn-Sn distances. The Eu atoms are embedded in this anionic substructure. Eu 2 Au 2 Sn 5 exhibits Curie-Weiss behavior above 50 K with an magnetic moment of 7.90 µ B per Eu atom indicating divalent europium. The compound shows metallic conduction with a specific resistivity of 150 µΩcm at room temperature. -

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