The Ternary Stannides MgRuSn4 and MgxRh3Sn7—x (x = 0.98—1.55)

The magnesium transition metal stannides MgRuSn₄ and Mg_xRh₃Sn_7—x (x = 0.98—1.55) were synthesized from the elements in glassy carbon crucibles in a water‐cooled sample chamber of a high‐frequency furnace. They were characterized by X‐ray diffraction on powders and single crystals. MgRuSn₄ adopts an ordered PdGa₅ type structure: I4/mcm, a = 674.7(1), c = 1118.1(2) pm, wR2 = 0.0506, 515 F² values and 12 variable parameters. The ruthenium atoms have a square‐antiprismatic tin coordination with Ru—Sn distances of 284 pm. These [RuSn_8/2] antiprisms are condensed via common faces forming two‐dimensional networks. The magnesium atoms fill square‐prismatic cavities between adjacent [RuSn₄] layers with Mg—Sn distances of 299 pm. The rhodium based stannides Mg_xRh₃Sn_7—x crystallize with the cubic Ir₃Ge₇ type structure, space groupe Im3m. The structures of four single crystals with x = 0.98, 1.17, 1.36, and 1.55 have been refined from X‐ray diffractometer data. With increasing tin substitution the a lattice parameter decreases from 932.3(1) pm for x = 0.98 to 929.49(6) pm for x = 1.55. The rhodium atoms have a square antiprismatic tin/magnesium coordination. Mixed Sn/Mg occupancies have been observed for both tin sites but to a larger extend for the 12d Sn2 site. Chemical bonding in MgRuSn₄ and Mg_xRh₃Sn_7—x is briefly discussed.     

Quaternary indides LaTIn3Mg (T = Rh and Ir) and CeIrIn3Mg with LaCoAl4 type structure

The quaternary indides LaTIn₃Mg (T = Rh and Ir) and CeIrIn₃Mg were prepared from the elements in sealed tantalum ampoules in an induction furnace. The samples were characterized by X-ray powder and single crystal data: LaCoAl₄ type, Pmma, Z = 2, a = 830.5(1), b = 436.1(1), c = 745.1(1) pm, wR2 = 0.038, 467 F ² values for LaRhIn_3.075Mg_0.925, a = 832.9(1), b = 436.5(1), c = 746.9(1) pm, wR2 = 0.077, 471 F ² values for LaIrIn_3.091Mg_0.909, and a = 832.2(1), b = 434.1(1), c = 743.9(1) pm, wR2 = 0.066, 465 F ² values for CeIrIn_3.07Mg_0.93 with 25 variables for each refinement. The transition metal, indium, and magnesium atoms build up three-dimensional [TIn₃Mg] networks which leave pentagonal prismatic voids for the lanthanum and cerium atoms. The transition metal atoms have tricapped trigonal prismatic coordination and the magnesium atoms fill distorted square prisms. All three crystals revealed a small degree of Mg/In mixing on the latter site.     

Rare‐Earth‐Rich Magnesium Compounds RE23Rh7Mg4 (RE = La,Ce, Pr,Nd, Sm,Gd) with Tetrahedral Mg4 Clusters

The rare earth‐rich compounds RE₂₃Rh₇Mg₄ (RE = La, Ce, Pr, Nd, Sm, Gd) were prepared by induction‐melting the elements in sealed tantalum tubes. The new compounds were characterized by X‐ray powder diffraction. They crystallize with the hexagonal Pr₂₃Ir₇Mg₄ type structure, space group P6₃mc. The structures of La₂₃Rh₇Mg₄ (a = 1019.1(1), c = 2303.7(4) pm, wR2 = 0.0827, 1979 F² values, 69 variables), Nd₂₃Rh₇Mg₄ (a = 995.4(2), c = 2242.3(5) pm, wR2 = 0.0592, 2555 F² values, 74 variables) and Gd₂₃Rh_6.86(5)Mg₄ (a = 980.5(2), c = 2205.9(5) pm, wR2 = 0.0390, 2083 F² values, 71 variables) were refined from single crystal X‐ray diffractometer data. The three crystallographically different rhodium atoms have trigonal prismatic rare earth coordination with short RE–Rh distances (283–300 pm in Nd₂₃Rh₇Mg₄). The prisms are condensed via common edges, leading to a rigid three‐dimensional network in which isolated Mg₄ tetrahedra (312–317 pm Mg–Mg in Nd₂₃Rh₇Mg₄) are embedded. Temperature dependent magnetic susceptibility data of Ce₂₃Rh₇Mg₄ indicate Curie‐Weiss behavior with an experimental magnetic moment of 2.52(1) μ_B/Ce atom, indicative for stable trivalent cerium. Antiferromagnetic ordering is evident at 2.9 K.     

New Indium‐Rich Compounds EuRhIn2 and EuRh2In8

EuRhIn₂ and EuRh₂In₈ were obtained by reacting the elements in sealed tantalum tubes in a high‐frequency furnace in a water‐cooled quartz glass sample chamber. Both indides were investigated by X‐ray powder and single crystal techniques: Cmcm, oC16, a = 432.2(1), b = 1058.8(1), c = 805.5(2) pm, wR2 = 0.0393, 471 F ² values, 16 variables for EuRhIn₂ and Pbam, oP44, a = 1611.8(2), b = 1381.7(2), c = 436.44(6) pm, wR2 = 0.0515, 1592 F ² values, 70 variables for EuRh₂In₈. EuRhIn₂ adopts the MgCuAl₂ type structure and may be considered as a rhodium filled variant of the binary Zintl phase EuIn₂. The indium substructure is homeotypic to the lonsdaleite type. Within the three‐dimensional [RhIn₂] polyanion the strongest bonding interactions occur for the Rh–In contacts followed by In–In. EuRh₂In₈ is the first indide with CaCo₂Al₈ type structure. The rhodium atoms have a trigonal prismatic indium coordination and the indium atoms form distorted indium centered InIn₈ cubes and InIn₁₀ pentagonal prisms with In–In distances ranging from 288 to 348 pm. Again, the rhodium and indium atoms together build a complex three‐dimensional [Rh₂In₈] polyanion in which the europium atoms are located within distorted pentagonal channels. Chemical bonding in EuRhIn₂ and EuRh₂In₈ is briefly discussed.     

Cobalt Centered Trigonal RE6 Prisms and Mg4 Clusters as Basic Structural Units in RE4CoMg (RE = Y,La, Pr,Nd, Sm,Gd–Tm)

The new rare earth metal rich intermetallic compounds RE₄CoMg (RE = Y, La, Pr, Nd, Sm, Gd–Tm) were prepared via melting of the elements in sealed tantalum tubes in a water‐cooled sample chamber of a high‐frequency furnace. The compounds were investigated by X‐ray diffraction of powders and single crystals: Gd₄RhIn type, , a = 1428.38(9) pm, wR2 = 0.0638, 680 F² values, 20 variables for La₄CoMg, a = 1399.5(2) pm, wR2 = 0.0584, 589 F² values, 20 variables for Pr₄CoMg, a = 1390.2(3) pm, wR2 = 0.0513, 634 F² values, 20 variables for Nd_3.90CoMg_1.10, a = 1381.0(3) pm, wR2 = 0.0730, 618 F² values, 22 variables for Sm_3.92Co_0.93Mg_1.08, a = 1373.1(4) pm, wR2 = 0.0586, 611 F² values, 20 variables for Gd_3.92CoMg_1.08, a = 1362.1(3) pm, wR2 = 0.0576, 590 F² values, 20 variables for Tb_3.77CoMg_1.23, a = 1344.8(2) pm, wR2 = 0.0683, 511 F² values, 20 variables for Dy_3.27CoMg_1.73, and a = 1343.3(2) pm, wR2 = 0.0560, 542 F² values, 20 variables for Er_3.72CoMg_1.28. The cobalt atoms have trigonal prismatic rare earth coordination. Condensation of the CoRE₆ prisms leads to a three‐dimensional network which leaves larger voids that are filled by regular Mg₄ tetrahedra at a Mg–Mg distance of 316 pm in La₄CoMg. The magnesium atoms have twelve nearest neighbors (3 Mg + 9 RE) in icosahedral coordination. In the structures with Nd, Sm, Gd, Tb, Dy, and Er, the RE1 positions which are not involved in the trigonal prismatic network reveal some RE1/Mg mixing and the Sm_3.92Co_0.93Mg_1.08 structure shows small cobalt defects. Considering La₄CoMg as representative of all studied systems an analysis of the chemical bonding within density functional theory closely reproduces the crystal chemistry scheme and shows the role played by the valence states of the different constituents in the electronic band structure. Strong bonding interactions were observed between the lanthanum and cobalt atoms within the trigonal prismatic network.     

Sc4Pt7Si2 – An Intergrowth Structure of ScPtSi and ScPt Related Slabs

The metal‐rich silicide Sc₄Pt₇Si₂ was synthesized by arc‐melting. Sc₄Pt₇Si₂ crystallizes with its own structure type, space group Pbam. The structure was refined from single‐crystal X‐ray diffractometer data: a = 647.6(1), b = 1617.1(3), c = 398.96(9) pm, wR2 = 0.0495, 807 F² values and 42 variables. Sc₄Pt₇Si₂ is an intergrowth structure of slightly distorted ScPtSi (TiNiSi type) and ScPt (CsCl type) related slabs. The silicon atoms have the typical coordination number 9 (4 Sc + 5 Pt) in the form of a tricapped trigonal prism. Together, the platinum and silicon atoms build up a complex three‐dimensional [Pt₇Si₂] network with short Pt–Si (238–246 pm) and Pt–Pt (282–303 pm) distances. The scandium atoms fill distorted square prismatic or pentagonal prismatic voids within this network, also with short Sc–Pt distances (276–308 pm). The structural difference of these two scandium species is reflected by substantial discrepancies in ⁴⁵Sc chemical shifts. The quadrupolar interaction parameters that were estimated from the nutation behavior of the two signals were used for an assignment to the two sites.     

The Solid Solution MgxIn3—xIr — Formation of the FeGa3 Type up to x = 0.73 and the Cementite Structure with x = 0.92

Various compounds within the solid solution Mg_xIn_3—xIr (x = 0—0.92) have been prepared from the elements by melting in glassy carbon crucibles in a water‐cooled sample chamber in a high‐frequency furnace. The structures of six single crystals with x = 0.25, 0.58, 0.62, 0.64, 0.71, and 0.73 have been refined from X‐ray diffractometer data. These intermetallics crystallize with the tetragonal FeGa₃ structure, space group P4₂/mnm: a = 700.6(1), c = 709.1(1) pm, wR2 = 0.0397, 296 F² values, 18 parameters for Mg_0.73In_2.27Ir. This structure is an intergrowth of AlB₂ and >W related slabs. The 4c and 8j indium sites show mixed occupancy with magnesium. For all crystals the 4c site within the cubes has a higher magnesium population. With increasing magnesium content, a switch in the structure type is observed. Mg_0.92In_2.08Ir adopts the Fe₃C structure, space group Pnma: a = 745.5(3), b = 837.7(3), c = 514.2(2) pm, wR2 = 0.0724, 738 F² values, 25 parameters. The iridium atoms are coordinated by eight (FeGa₃ type) and nine (Fe₃C type) indium/magnesium atoms in both structure types. The FeGa₃ and the Fe₃C type both derive from the aristotype U₃Si₂ as presented by a group‐subgroup scheme.     

Nd4.67Ru3Mg8.83 – A Magnesium‐rich Compound with Ru@Mg4Nd4 Square Antiprisms and Mg@Mg8 Cubes as ­Basic Building Units

The magnesium‐rich intermetallic compound Nd_4.67Ru₃Mg_8.83 was synthesized from the elements in a sealed tantalum tube in a resistance furnace. Nd_4.67Ru₃Mg_8.83 was characterized by X‐ray powder and single crystal diffraction: new structure type,I4/mmm, tI66, a = 946.0(1), c = 1789.5(4) pm, wR2 = 0.0368, 725 F² values and 36 variables. Two of the five crystallographically independent magnesium sites show a small degree of Mg/Nd mixing. The ruthenium atoms have square anti‐prismatic Nd₄Mg₄ coordination. Always six of such anti‐prisms are condensed via common edges, leading to a CsCl analogous neodymium coordination for the Mg4 atoms. The two‐dimensional networks of edge‐sharing Ru@Nd₄Mg₄ antiprisms are condensed to a three‐dimensional network via Mg5@Mg3₄Mg1₄ cubes. The extended magnesium substructure shows a broad range of Mg–Mg distances from 308 to 351 pm.     

Syntheses and Structures of RE4Pt10In21 (RE = La–Nd)

The isotypic indides RE₄Pt₁₀In₂₁ (RE = La, Ce, Pr, Nd) were prepared by melting mixtures of the elements in an arc‐furnace under an argon atmosphere. Single crystals were synthesized in tantalum ampoules using special temperature modes. The four samples were studied by powder and single crystal X‐ray diffraction: Ho₄Ni₁₀Ga₂₁ type, C2/m, a = 2305.8(2), b = 451.27(4), c = 1944.9(2) pm, β = 133.18(7)°, wR2 = 0.045, 2817 F² values, 107 variables for La₄Pt₁₀In₂₁, a = 2301.0(2), b = 448.76(4), c = 1941.6(2) pm, β = 133.050(8)°, wR2 = 0.056, 3099 F² values, 107 variables for Ce₄Pt₁₀In₂₁, a = 2297.4(2), b = 447.4(4), c = 1939.7(2) pm, β = 132.95(1)°, wR2 = 0.059, 3107 F² values, 107 variables for Pr₄Pt₁₀In₂₁, and a = 2294.7(4), b = 446.1(1), c = 1938.7(3) pm, β = 132.883(9)°, wR2 = 0.067, 2775 F² values, 107 variables for Nd₄Pt₁₀In₂₁. The 8j In2 positions of all structures have been refined with a split model. The In1 sites of the lanthanum and the cerium compound show small defects, leading to the refined composition La₄Pt₁₀In_20.966(6) and Ce₄Pt₁₀In_20.909(6) for the investigated crystals. The same position shows Pt/In mixing in the praseodymium and neodymium compound leading to the refined compositions Pr₄Pt_10.084(9)In_20.916(9) and Nd₄Pt_10.050(9)In_20.950(9). All platinum atoms have a tricapped trigonal prismatic coordination by rare‐earth metal and indium atoms. The shortest interatomic distances occur for Pt–In followed by In–In. Together, the platinum and indium atoms build up three‐dimensional [Pt₁₀In₂₁] networks in which the rare earth atoms fill distorted pentagonal tubes. The crystal chemistry of RE₄Pt₁₀In₂₁ is discussed and compared with the RE₄Pd₁₀In₂₁ indides and isotypic gallides.     

Ternary Indides RE4Pd10In21 (RE = La,Ce, Pr,Nd, Sm) — Synthesis,Structure, and Physical Properties

The ternary indium compounds RE₄Pd₁₀In₂₁ (RE = La, Ce, Pr, Nd, Sm) were synthesized from the elements in glassy carbon crucibles in a high‐frequency furnace. Single crystals of Sm₄Pd₁₀In₂₁ were obtained from an indium flux. An arc‐melted precursor alloy of the starting composition ～SmPd₃In₆ was annealed with a slight excess of indium at 1200 K followed by slow cooling (5 K/h) to 870 K. All compounds were investigated by X‐ray powder diffraction and the structures were refined from single crystal diffractometer data. The RE₄Pd₁₀In₂₁ indides are isotypic with Ho₄Ni₁₀Ga₂₁, space group C2/m: a = 2314.3(2), b = 454.70(7), c = 1940.7(2) pm, β = 133.43(2)°, wR2 = 0.0681, 1678 F² values for La₄Pd₁₀In₂₁, a = 2308.2(1), b = 452.52(4), c = 1944.80(9) pm, β = 133.40(1)°, wR2 = 0.0659, 1684 F² values for Ce₄Pd₁₀In₂₁, a = 2303.8(2), b = 450.78(4), c = 1940.6(1) pm, β = 133.39(1)°, wR2 = 0.0513, 1648 F² values for Pr₄Pd₁₀In₂₁, a = 2300.2(2), b = 449.75(6), c = 1937.8(2) pm, β = 133.32(1)°, wR2 = 0.1086, 1506 F² values for Nd₄Pd₁₀In₂₁, and a = 2295.6(2), b = 447.07(4), c = 1935.7(1) pm, β = 133.16(1)°, wR2 = 0.2291, 2350 F² values for Sm₄Pd₁₀In₂₁, with 108 variables per refinement. All palladium atoms have a trigonal prismatic coordination. The strongest bonding interactions occur for the Pd—In and In—In contacts. The structures are composed of covalently bonded three‐dimensional [Pd₁₀In₂₁] networks in which the rare earth metal atoms fill distorted pentagonal channels. The crystal chemistry and chemical bonding in these indides is briefly discussed. Magnetic susceptibility measurements show diamagnetism for La₄Pd₁₀In₂₁ and Curie‐Weiss paramagnetism for Ce₄Pd₁₀In₂₁, Pr₄Pd₁₀In₂₁, and Nd₄Pd₁₀In₂₁. The neodymium compound orders antiferromagnetically at T_N = 4.5(2) K and undergoes a metamagnetic transition at a critical field of 1.5(2) T. All the RE₄Pd₁₀In₂₁ indides studied are metallic conductors.     

Syntheses and Crystal Structures of LaRhMg,CeRhMg, PrRhMg,and NdRhMg

New intermetallic rare earth compounds LaRhMg, CeRhMg, PrRhMg, and NdRhMg were prepared by reaction of the elements in sealed tantalum tubes in a high‐frequency furnace. The compounds were investigated by X‐ray diffraction both on powders and single crystals. LaRhMg crystallizes with the LaNiAl type structure, space group Pnma, Z = 8, a = 760.1(2), b = 419.92(8), c = 1702.6(2) pm, wR2 = 0.0482, 740 F² values and 38 variable parameters. The cerium compound adopts the ZrNiAl structure: P6¯2m, Z = 3, a = 752.3(1), c = 417.6(1) pm, wR2 = 0.0497, 250 F²2 values and 17 variable parameters. PrRhMg and NdRhMg crystallize with the TiNiSi type: Pnma, Z = 4, a = 721.62(7), b = 415.98(4), c = 869.47(8) pm, wR2 = 0.1864, 440 F² values, 20 variables for PrRhMg and a = 720.6(1), b = 417.6(1), c = 868.8(1) pm, wR2 = 0.0779, 425 F² values, 22 variables for NdRhMg. Refinements of the occupancy parameters revealed mixed Mg/Rh occupancy for the magnesium sites of the cerium and the neodymium compound leading to the compositions CeRh_1.262(8)Mg_0.738(8) and NdRh_1.114(9)Mg_0.886(9) for the investigated single crystals. From a geometrical point of view, the four crystal structures are built up from different rhodium centered trigonal prisms. The rhodium and magnesium atoms form three‐dimensional [RhMg] networks in which the rare earth metal atoms are located in different types of channels. The networks show Rh—Mg and Mg—Mg bonding.     

Infinite Gold Zig‐Zag Chains as Structural Motif in Ca3Au3In – A Ternary Ordered Variant of the Ni4B3 Type

New auride Ca₃Au₃In was synthesized from the elements in a sealed tantalum tube in a high‐frequency furnace. Ca₃Au₃In was investigated by X‐ray powder and single crystal diffraction: ordered Ni₄B₃ type, Pnma, a = 1664.1(6), b = 457.3(2), c = 895.0(3) pm, wR2 = 0.0488, 1361 F² values, and 44 variables. The three crystallographically independent boron positions of the Ni₄B₃ type are occupied by the gold atoms, while the four nickel sites are occupied by calcium and indium in an ordered manner. All gold atoms have trigonal prismatic coordination, i.e. Ca₆ prisms for Au1 and Au2 and Ca₄In₂ prisms for Au3. While the Au3 atoms are isolated, we observe Au1–Au1 and Au2–Au2 zig‐zag chains at Au–Au distances of 292 and 284 pm. These slabs resemble the CrB type structure of CaAu. Consequently Ca₃Au₃In can be considered as a ternary auride. Together the Au2, Au3 and indium atoms build up a three‐dimensional [Au₂In] polyanionic network (281–293 pm Au–In) in which the chains of Au1 centered trigonal prisms are embedded. The crystal chemical similarities with the structures of Ni₄B₃, CaAuIn, and CaAu are discussed.     

EuIrIn4 with LaCoAl4 Type Structure – Synthesis,Magnetic Properties,and 151Eu Mössbauer Spectroscopy

LaCoAl₄ type EuIrIn₄ was synthesized by induction-melting of the elements in a sealed tantalum ampoule, followed by annealing of the sample in a high-frequency or in a muffle furnace. The EuIrIn₄ structure was refined from single-crystal X-ray diffraction data: Pmma, a = 860.65(3), b = 430.33(6), c = 757.65(7) pm, wR = 0.0748, 633 F² values and 24 variables. The striking building units are iridium-centered trigonal prisms of indium atoms, distorted bcc indium cubes and a pentagonal prismatic indium coordination of the europium atoms. Within the three-dimensional [IrIn₄]^2– polyanionic network the Ir–In and In–In distances range from 260–288 pm and 306–332 pm, respectively. The divalent ground state of europium was manifested through magnetic [7.96(1) μ_B / Eu atom, T_N = 7.9(1) K] and ¹⁵¹Eu Mössbauer spectroscopic data [δ = –10.54(2) mm · s^–1; B_hf = 19.1(1) T at 6 K].     

Rare Earth-Rich Indides <Emphasis Type="Italic">RE</Emphasis><Subscript>5</Subscript>Pt<Subscript>2</Subscript>In<Subscript>4</Subscript> (<Emphasis Type="Italic">RE</Emphasis> = Sc,Y, La–Nd,Sm, Gd–Tm,Lu)

Summary. The isotypic indides RE ₅Pt₂In₄ (RE = Sc, Y, La–Nd, Sm, Gd–Tm, Lu) were synthesized by arc-melting of the elements and subsequent annealing. They were investigated via X-ray powder diffraction. Small single crystals of Gd₅Pt₂In₄ were grown via slow cooling and the structure was refined from X-ray single crystal diffractometer data: Pbam, a = 1819.2(9), b = 803.2(3), c = 367.6(2) pm, wR ² = 0.089, 893 F ² values and 36 parameters. The structure is an intergrowth variant of distorted trigonal and square prismatic slabs of compositions GdPt and GdIn. Together the platinum and indium atoms build up one-dimensional [Pt₂In₄] networks (292–333 pm Pt–In and 328–368 pm In–In) in an AA stacking sequence along the c axis. The gadolinium atoms fill distorted square and pentagonal prismatic cages between these networks with strong bonding to the platinum atoms.     

Crystal Structure of ϵ‐Ag7+xMg26–x – A Binary Alloy Phase of the Mackay Cluster Type

The binary alloy phase ϵ‐Ag_7+xMg_26–x with x ≈ 1 and small amounts of the β′‐AgMg phase crystallize by annealing of Ag–Mg alloys with starting compositions between 24–28 At‐% Ag at 390 to 420 °C. A model structure for the ϵ‐phase consisting of a fcc packing of Mackay clusters was derived from the known structure of the ϵ′‐Ag₁₇Mg₅₄ phase. Crystals of the ϵ‐phase were obtained by direct melting of the elements and annealing. The examination of a single crystal yielded a face‐centered cubic unit cell, space group Fm3 with a = 1761.2(5) pm. The refinement was started with the parameters of the model: wR2(all) = 0.0925 for 1093 symmetrically independent reflections. A refinement of the occupancy parameters indicated a partial replacement of silver for magnesium at two metal atom sites, resulting in the final composition ϵ‐Ag_7+xMg_26–x with x = 0.96(2). There are 264 atoms in the unit cell and the calculated density is 3.568 gcm^–3. The topology of the model was confirmed. Mackay icosahedra are located at the lattice points of a face‐centered cubic lattice. Differences between model and refined structure and their effects on the powder patterns are discussed. The new binary structure type of ϵ‐Ag_7+xMg_26–x can be described in terms of the I3‐cluster concept.     

Ca2Pd2In and Ca2Pt2In with Monoclinic HT‐Pr2Co2Al Type Structure

The metal‐rich indides Ca₂Pd₂In and Ca₂Pt₂In were synthesised from the elements in sealed tantalum ampoules in an induction furnace. Both samples were investigated by X‐ray powder and single crystal diffraction: HT‐Pr₂Co₂Al type, C2/c, a = 1017.6(5), b = 574.1(3), c = 812.7(3) pm, β = 104.54(2)°, wR2 = 0.0344, 590 F² values for Ca₂Pd₂In and a = 1004.3(3), b = 568.9(1), c = 813.1(2) pm, β = 104.25(2)°, wR2 = 0.0435, 654 F² values for Ca₂Pt₂In with 25 variables per refinement. The structure contain Pd₂ (272 pm) and Pt₂ (264 pm) dumb‐bells with a trigonal prismatic coordination for each transition metal atom. These AlB₂ related slabs are condensed via common edges. Together the palladium and indium atoms build up three‐dimensional [Pd₂In] and [Pt₂In] polyanionic networks in which the calcium atoms fill larger channels. The bonding of calcium to the network proceeds via shorter Ca–Pd and Ca–Pt contacts. Ca₂Pd₂In and Ca₂Pt₂In are Pauli paramagnets.     

Intermetallic Gold Compounds REAuMg (RE = Y,La–Nd,Sm, Eu,Gd–Yb)

New intermetallic rare earth compounds REAuMg (RE = Y, La–Nd, Sm, Eu, Gd–Yb) were synthesized by reaction of the elements in sealed tantalum tubes in a high‐frequency furnace. The compounds were investigated by X‐ray diffraction both on powders and single crystals. Some structures were refined on the basis of single crystal data. The compounds with Y, La–Nd, Sm, and Gd–Tm adopt the ZrNiAl type structure with space group P62m: a = 770.8(2), c = 419.5(1) pm, wR2 = 0.0269, 261 F² values for PrAuMg, a = 750.9(2), c = 407.7(1) pm, wR2 = 0.0561, 649 F² values for HoAuMg with 15 variables for each refinement. Geometrical motifs in HoAuMg are two types of gold centered trigonal prisms: [Au1Mg₃Ho₆] and [Au2Mg₆Ho₃]. The gold and magnesium atoms form a three‐dimensional [AuMg] polyanion in which the holmium atoms fill distorted hexagonal channels. The magnesium positions show a small degree of magnesium/gold mixing resulting in the refined compositions PrAu_1.012(2)Mg_0.988(2) and HoAu_1.026(3)Mg_0.974(3). EuAuMg and YbAuMg contain divalent europium and ytterbium, respectively. Both compounds crystallize with the TiNiSi type structure, space group Pnma: a = 760.6(3), b = 448.8(2), c = 875.8(2) pm, wR2 = 0.0491, 702 F² values, 22 variables for EuAuMg, and a = 738.4(1), b = 436.2(1), c = 864.6(2) pm, wR2 = 0.0442, 451 F² values, and 20 variables for YbAuMg. The europium position shows a small degree of europium/magnesium mixing, and the magnesium site a slight magnesium/gold mixing leading to the refined composition Eu_0.962(3)Au_1.012(3)Mg_1.026(3). No mixed occupancies were found in YbAuMg where all sites are fully occupied. In these structures the europium(ytterbium) and magnesium atoms form zig‐zag chains of egde‐sharing trigonal prisms which are centered by the gold atoms. As is typical for TiNiSi type compounds, also in EuAuMg and YbAuMg a three‐dimensional [AuMg] polyanion occurs in which the europium(ytterbium) atoms are embedded. The degree of distortion of the two polyanions, however, is different.     

Magnesium‐Tin Substitution in NiMg2

The binary intermetallic compound NiMg₂ (own structure type) forms a pronounced solid solution NiMg_2?xSn_x. The structure of NiMg_1.85(1)Sn_0.15(1) was refined on the basis of single crystal X‐ray data: P6₄22, a = 520.16(7), c = 1326.9(1) pm, wR2 = 0.0693, 464 F² values, and 20 variables. With increasing magnesium/tin substitution, the structure type changes. Crystals with x = 0.22 and 0.40 adopt the orthorhombic CuMg₂ type: Fddd, a = 911.0(2), b = 514.6(1), c = 1777.0(4) pm, wR2 = 0.0427, 394 F² values for NiMg_1.78(1)Sn_0.22(1), and a = 909.4(1), b = 512.9(1), c = 1775.6(1) pm, wR2 = 0.0445, 307 F² values for NiMg_1.60(1)Sn_0.40(1) with 19 variables per refinement. The nickel atoms build up almost linear chains with Ni–Ni distances between 260 and 263 pm in both modifications where each nickel atom has coordination number 10 with two nickel and eight Mg/Sn neighbors. Both magnesium sites in the NiMg₂ and CuMg₂ type structures show Mg/Sn mixing. The Ni polyhedra are condensed leading to dense layers which show a different stacking sequence in both structure types. The crystal chemical peculiarities of these intermetallics are briefly discussed.     

Gd3Pt4In12 and Tb3Pt4In12 — New Ternary Indides with Condensed Distorted [PtIn6] Trigonal Prisms

The ternary indium compounds Gd₃Pt₄In₁₂ and Tb₃Pt₄In₁₂ were synthesized from an indium flux. Arc‐melted precursor alloys with the starting compositions ∼GdPtIn₄ and ∼TbPtIn₄ were annealed with a slight excess of indium at 1200 K followed by slow cooling (5 K/h) to 870 K. Both compounds were investigated by X‐ray powder diffraction: a = 990.5(1), c = 1529.5(3) pm for Gd₃Pt₄In₁₂ and a = 988.65(9), c = 1524.0(1) pm for Tb₃Pt₄In₁₂. The structure of the gadolinium compound was solved and refined from single crystal X‐ray data: P3¯m1, wR2 = 0.0470, 1469 F² values and 62 variable parameters. Both crystallographically different platinum sites have a slightly distorted trigonal prismatic indium coordination. These [PtIn₆] prisms are condensed via common edges and corners forming a complex three‐dimensional [Pt₁₂In₃₂] network. The gadolinium, In1 and In7 atoms fill cavities within this polyanion. Tb₃Pt₄In₁₂ is isotypic with the gadolinium compound.     

Trivalent‐Intermediate Valent Cerium Ordering in CeRuSn – A Static Intermediate Valent Cerium Compound with a Superstructure of the CeCoAl Type

New equiatomic stannide CeRuSn was synthesized from the elements by arc‐melting. CeRuSn was investigated by X‐ray powder and single crystal diffraction: C2/m, a = 1156.1(4), b = 475.9(2) and c = 1023.3(4) pm, β = 102.89(3)°, wR2 = 0.0466, 1229 F² values and 38 variables. CeRuSn adopts a superstructure of the monoclinic CeCoAl type through a doubling of the subcell c axis. In the superstructure two crystallographically independent cerium sites occur. Based on the interatomic distances the two sites can be assigned to trivalent Ce2 and intermediate valent Ce1. This trivalent‐intermediate valent cerium ordering is underlined by magnetic susceptibility measurements χ_m(T): below 150 K χ_m, measured with decreasing temperature, follows a Curie‐Weiss law χ_m = C_m/(T–θ_p) giving C_m = 0.38 emuK/mol as Curie constant per CeRuSn mol; a value showing that only half of the cerium atoms are trivalent in CeRuSn (C_m = 0.807 emuK/mol for one free Ce³⁺ ion). A remarkable feature of the CeRuSn structure are the short Ce1–Ru1 (233 pm) and Ce1–Ru2 (246 pm) distances. The crystal chemistry of CeRuSn is discussed on the basis of a group‐subgroup scheme.