At 320 K, the crystal structure of CeRuSn is commensurate with the related CeCoAl-type of structure by the doubling of the c lattice parameter. However, with lowering the temperature it becomes incommensurate with x and z position parameters at all three elemental sites being modulated as one moves along the c-axis. The resulting crystal structure can be conveniently described within the superspace formalism in (3 + 1) dimensions. The modulation vector, after initially strong temperature dependence, approaches a value close to qnuc = (0 0 0.35). Below TN = 2.8 (1) K, CeRuSn orders antiferromagnetically with a propagation vector qmag = (0 0 0.175), i.e. with the magnetic unit cell doubled along the c-axis direction with respect to the incommensurate crystal structure. Ce moments appear to be nearly collinear, confined to the a-c plane, forming ferromagnetically coupled pairs. Their magnitudes are modulated between 0.11 and 0.95 μB as one moves along the c-axis.

Well-shaped single crystals of binary AuSn 2 were obtained as a side product during the synthesis of LiAu 3 Sn 4 . The structure of AuSn 2 has been studied by X-ray diffractometer data: Pbca, Z = 8, a = 689.8(1), b = 701.1(1), c = 1177.3(2) pm, wR2 = 0.0533, 1234 F 2 values, and 29 variables. The gold atoms show a distorted octahedral coordination by tin at Au-Sn distances ranging from 272 to 283 pm. The structure can be considered as an intergrowth of pyrite and marcasite related slabs. Consequently one observes Sn1-Sn2 dumb-bells with a Sn-Sn distance of 289 pm, while all other Sn-Sn distances are larger than 322 pm.

CeRhSb was prepared from the elements by arc-melting. A single crystal of this antimonide was investigated on the basis of X-ray diffractometer data: TiNiSi type; Pnma; a = 741.58(9), b = 461.80(9), c = 785.77(8) pm; wR2 = 0.0960; 645 F-2 values; 20 variable parameters. Hydrogenation leads to the formation of the new hydride CeRhSbH0.2 which adopts the same structure but with a slightly larger unit cell volume: a = 742.2(2), b = 462.5(2), c = 787.7(2) pm; wR2 = 0.1444; 443 F-2 values; 20 variable parameters. The rhodium and antimony atoms build up three-dimensional [RhSb] networks with Rh-Sb distances ranging from 268 to 287 pm. The cerium atoms fill distorted hexagonal channels within these networks with one short Ce-Rh contact (310 pm in CeRhSb and 311 pm in CeRhSbH0.2). Susceptibility and specific heat measurements on CeRhSbH0.2 reveal antiferromagnetic ordering at T-N = 3.6(2) K. The experimental magnetic moment in the paramagnetic region is 2.68(5) mu(B)/Ce atom. Magnetization measurements below T-N reveal a spin-flip transition in the range 1.6-2.4 T. Resistivity data show metallic behavior and the characteristics of a Kondo system. Thermoelectric power measurements show a distinct maximum around 106 K with a value of 24 mu V/K. Sb-121 Mossbauer spectroscopic data for CeRhSb and CeRhSbH0.2 at 78 K show only one antimony site. The isomer shift is slightly smaller for the hydrogenated sample indicating a slightly higher electron density at the antimony nuclei of CeRhSbH0.2.

The indide SmRhIn (ZrNiAl type, P6̅2̅m, a = 750.93(8), c = 397.52(4) pm) was synthesized from the elements by arc-melting. SmRhIn orders antiferromagnetically at 8.0(5) K. The non-linearity of the temperature dependence of the inverse susceptibility points to a large van Vleck term for the samarium atoms. Magnetization measurements indicate a metamagnetic transition at a flux density of 3 T.

The rare earth transition metal carbides Sc3RhC4 and Sc3IrC4 were synthesized by arc-melting of cold-pressed pellets of the elements (ideal atomic ratio) under an atmosphere of purified argon. The structures of the two carbides were investigated by X-ray diffraction on both powders and single crystals. Sc3RhC4 and Sc3IrC4 crystallize with a pronounced Sc3CoC4 type subcell, space group Immm. Weak additional reflections indicated the formation of a superstructure by doubling the subcell along with a monoclinic distortion. The superstructure of Sc3RhC4 and Sc3IrC4 was refined from X-ray single crystal diffractometer data: C12/m1, a=560.16(5), b=1225.8(1), c=560.16(5)pm, β=106.08(1)°, wR2=0.1129, 821 F2 values for Sc3RhC4 and a=559.96(4), b=1224.1(1), c=559.94(4)pm, β=105.35(1)°, wR2=0.0562, 816 F2 values for Sc3IrC4 with 32 variables per refinement. The formation of the superstructure is explained on the basis of a group-subgroup scheme. Both structures are composed of one-dimensional infinite polyanionic layers [T(C2)2]n (T=Rh, Ir) that are separated by the scandium atoms. While these polyanionic layers are planar in the Sc3CoC4 type structure, a slight puckering occurs in Sc3RhC4 and Sc3IrC4. An ionic formula splitting can to a first approximation be written as (3Sc3+)[TC4]9−. Chemical bonding in Sc3RhC4 and Sc3IrC4 is briefly discussed.

The gadolinium-rhodium-indide Gd3Rh1.940(7)In4 was prepared by arc-melting of the elements and subsequent annealing in a corundum crucible in a sealed silica tube. Gd3Rh1.940( 7) In4 adopts the hexagonal Lu3Co1.87In4 type, space group P (6) over bar, a = 781.4(5), c = 383.8(3) pm, wR2 = 0.0285, BASF = 0.375( 1) (merohedric twinning via a twofold axis (xx0)), 648 F 2 values, 22 variables. The structure is derived from the well known ZrNiAl type through an ordering of rhodium and indium atoms on the Ni2 sites. The Rh/In ordering forces a reduction of the space group symmetry from P (6) over bar 2m to P (6) over bar, leading to merohedric twinning for the investigated crystal. The Rh1 site has an occupancy of only 94.0(7)%. The investigated crystal had a composition Gd3Rh1.940(7)In4. The main geometrical motif are three types of centered, tricapped trigonal prisms, i.e., [Rh1In2(6)Gd(3)], [Rh2Gd(6)In2(3)], and [In1Gd(6)In2(3)]. The shortest interatomic distances occur for Rh-In (276-296pm) followed by In-In (297pm). Together, the rhodium and indium atoms build up a three-dimensional [Rh1.940(7)In4] network, in which the gadolinium atoms fill slightly distorted pentagonal channels. The crystal chemistry of Gd3Rh1.940(7) In-4 is discussed on the basis of a group-subgroup scheme.

The technologically important S-phase precipitate MgCuAl2 has been synthesized from the elements in a sealed tantalum tube in an induction furnace. The aluminide was investigated by powder and single crystal X-ray diffraction methods: Cmcm, a = 401.19(9), b = 926.5(2), c = 712.4(1) pm, wR2 = 0.0425, 234 F2 values, and 16 variable parameters. The new crystallographic data fully confirm the original work by Perlitz and Westgren [Ark. Kemi, Mineral. Geol. 16, 1 (1943)], but the present structure refinement has led to a much higher precision. The crystal chemical peculiarities of MgCuAl2 are briefly discussed.

The high-pressure (HP) modification of CePtSn was prepared under multianvil high-pressure (9.2 GPa) high-temperature (1325 K) conditions from the normal-pressure (NP) modification. Both modifications were investigated by powder and single crystal X-ray data: TiNiSi type, Pnma, a = 746.89(9), b = 462.88(4), c = 801.93(7) pm, wR2 = 0.0487, 452 F2 values, 20 variable parameters for NP-CePtSn, and ZrNiAl type, P6̅2m, a = 756.919(5), c = 415.166(4) pm, wR2 = 0.0546, 252 F2 values, 14 variable parameters for HP-CePtSn. Both modifications are built up from platinumcentered trigonal prisms. Together, the platinum and tin atoms form different three-dimensional [PtSn] networks in which the cerium atoms fill channels. The crystal chemistry and chemical bonding of NP- and HP-CePtSn is discussed. Susceptibility measurements of HP-CePtSn indicate Curie-Weiss behavior above 40 K with an experimental magnetic moment of 2.55(1) μB/Ce atom, indicating trivalent cerium. No magnetic ordering could be detected down to 2 K.

Ternary silicides RE2RE′3 Si4 (RE = La, Ce; RE′= Y, Lu) were synthesized by arc-melting of the elements. Single crystals were grown by annealing the arc-molten buttons slightly below the melting points in water-cooled silica tubes in an induction furnace. Five silicides RE2RE3′Si4 were investigated by X-ray powder and single crystal diffraction: Zr5Si4 type, P41212, a = 779.4(3), c = 1441.3(9) pm, wR2 = 0.072, 1806 F2 values, 45 variables for La1.72(4)Y3.28(4)Si4, P43212, a = 769.92(7), c = 1412.3(1) pm, wR2 = 0.079, 1846 F2 values, 45 variables, BASF = 0.36(4) for La1.72(2)Lu3.28(2)Si4, P41212, a = 778.6(1), c = 1433.9(3) pm, wR2 = 0.054, 1910 F2 values, 46 variables, BASF = 0.34(4) for Ce1.82(6)Lu3.18(6)Si4, P43212, a = 778.8(3), c = 1436.0(10) pm, wR2 = 0.166, 1916 F2 values, 45 variables for Ce1.71(7)Y3.29(7)Si4, and Sm5Ge4 type, Pnma, a = 749.2(2), b = 1484.2(7), c = 780.3(2) pm, wR2 = 0.070, 1956 F2 values and 49 variables for Ce1.47(3)Y3.53(3)Si4. The local coordinations of both structure types are very similar, i. e. CN 18, 16, and 14 coordination polyhedra for the RE1, RE2, and RE3 atoms. The main structural motif is the eightfold coordination of the RE3 positions by rare earth metal atoms. These slightly distorted RERE’8 cubes are condensed via common corners (Zr5Si4 type) or via common edges (Sm5Ge4 type). All silicon atoms in these silicides form Si2 pairs at Si-Si distances ranging from 254 to 258 pm. DFT band structure calculations confirm the metallic character of both silicides and the trivalent state of cerium in Ce5Si4. The COHP analysis (Crystal Orbital Hamilton Population) of the Si-Si bonds shows a significant occupation of Si-Si antibonding orbitals, which is partially compensated by a Si-Si π*,σ*Y-4d (Ce-5d) back donation.

Abstract The ternary stannide SrAuSn2 was synthesized by induction melting of the elements under an argon atmosphere in a sealed niobium ampoule in a water-cooled sample chamber of a high-frequency furnace. The structure of SrAuSn2 was investigated by X-ray powder and single crystal diffraction. It was found to be favourable to describe as a commensurately modulated structure. The 3+1 dimensional superspace group symmetry P : Cmcm(α, 0, 0) : 0s0 with the unit cell dimensions a = 460.20(14), b = 2038.8(8), c = 460.34(19) pm and the modulation wave vector q =¼ [100]*. The Sn1 atoms were those with the strongest modulation while the rest of the atoms showed rather small deviations from the average structure. The SrAuSn2 structure is closely related to the CeNiSi2 type. Geometrically these structures are built up from distorted ThCr2Si2 and AlB2 slabs. The gold atoms are located in the ThCr2Si2 slab. They have a distorted square pyramidal tin coordination at Au-Sn distances ranging from 266 to 294 pm. These pyramids are condensed via common edges forming two-dimensional layers. The latter are condensed via the Sn1 atoms within the AlB2 slabs that form one-dimensional zigzag chains with Sn1-Sn1 distances ranging from 282 to 288 pm. These chains show the strong modulations. Together, the gold and tin atoms build up a three-dimensional [AuSn2] network, in which the strontium atoms fill distorted hexagonal channels.

GdAuMg was synthesized by reaction of the elements in a sealed tantalum ampule in a high-frequency furnace. The structure was investigated by X-ray diffraction on both powders and single crystals: ZrNiAl type, P (6) over bar 2m, a = 756.3(1), c = 412.71(7) pm, wR2 = 0.0285 for 308 F-2 values, 14 variables. Geometrical motifs of the GdAuMg structure are gold centered tricapped trigonal prisms [Au1Mg(3)Gd(6)] and [Au2Mg6Gd3]. Together the gold and magnesium atoms form a three-dimensional [AuMg] network in which the gadolinium atoms fill distorted hexagonal channels. Bulk magnetic properties have been investigated by means of AC and DC magnetic susceptibility measurements and Gd-155 Mossbauer spectroscopy was used to monitor the local electronic and magnetic structure. Two magnetic phase transitions were found. One transition, at T-1 = T-N = 81.1 (1) K, is from a paramagnetic to an antiferromagnetic state of collinear character and the other at T-2 = 19.0(1) from the antiferromagnetic to a kind of canted magnetic ordering characterized by a very narrow hysteresis loop. (C) 2004 Elsevier SAS. All rights reserved.

New ternary indides RE10Rh9+/-xIn20 (RE = Y, Tb-Tm, Lu) were synthesized from the elements by arc-melting under argon and subsequent annealing in alumina or tantalum crucibles. YbRhIn2 was prepared in a sealed tantalum ampoule in an induction furnace. X-ray powder and single crystal data for RE10Rh9+xIn20 revealed isotypy with the tetragonal Ho10Ni9In20 type structure, space group P4/nmm. A crystal of Tm10Rh9In20 shows the ideal composition: a = 1335.42(7), c = 921.26(6) pm, wR2 = 0.0524, 1460 F-2 values and 62 variable parameters, while the RE10Rh9In20 indides with the lighter rare earth metals contain an additional rhodium site leading to a homogeneity range according to RE10Rh9+/-xIn20. This was manifested from X-ray single crystal data for Y10Rh9.19(1)In20, Tb10Rb9.40(1)In20, Dy10Rh9.07(1)In20, Dy10Rh9.52(1)In20, Ho10Rh9.41(1)In20, and Er10Rh9.27(1)In20. On the other hand, defects were found for the Rh2 site of Lu10Rh8.87(1)In20. The crystal chemistry of the RE10Rh9In20 indides and the structurally related REPdIn2 indides with tetragonal HfNiGa2 structure is discussed. YbRhIn2 was synthesized in a sealed tantalum ampoule. It adopts the orthorhombic MgCuAl2 type structure: Cmcm, a = 418.24(6), b = 1024.0(2), c 807.5(l) pm, wR2 = 0.0477, 292 F-2 values and 16 variable parameters. The rhodium atoms fill distorted triangles of an orthorhombically distorted YbIn2 substructure.

The binary transition metal magnesium compounds RhMg3 and Ir3Mg13 have been synthesized from the elements in sealed niobium tubes and investigated on the basis of X-ray powder and single crystal data: Cu3P type, P63cm, a = 790.5(4), c = 825.6(3) pm, wR2 = 0.0244, 344 F2 values, 27 variable parameters for RhMg3, and R3̅c, a = 1607.0(2), c = 844.88(9) pm, wR2 = 0.0535, 656 F2 values, 29 variable parameters for Ir3Mg13. The rhodium atoms in RhMg3 have coordination number 11. These polyhedra show an AB AB stacking sequence like in the hexagonal close-packed structure. The crystal chemical relation of the Cu3P type structure of RhMg3 with the aristotype Na3As (IrAl3) is discussed on the basis of a group-subgroup scheme. Ir3Mg13 crystallizes with a new complex structure type with coordination numbers of 11, 14, 15, 14, and 12 for the Ir, Mg1, Mg2, Mg3, and Mg4 atoms, respectively

The ternary scandium transition metal indides Sc3Ni2.10(5)In3.60(5), Sc3 Ni2.14(2)In3.76(2), ScPd0.981(2)In, and Sc3Rh1.594(9)In4 have been synthesized from the elements in glassy carbon crucibles in a high frequency furnace or by arc-melting. They have been investigated by X-ray powder diffraction and the structures refined on the basis of single crystal diffractometer data: Lu3Co1.87In4 type, P6̄, a = 745.7(1), c = 342.85(7) pm, wR2 = 0.0689, 545 F2, 24 parameters for Sc3Ni2.10(5)In3.60(5), a = 753.63(7), c = 344.3(1) pm, wR2 = 0.0362, 792 F2, 22 parameters for Sc3Ni2.14(2)In3.76(2), P6̄2m, ZrNiAl type, a = 764.1(2), c = 345.90(8) pm, wR2 = 0.0333, 326 F2, 15 parameters for ScPd0.981(2)In, and P6̄, a = 769.4(1), c = 684.1(1) pm, wR2 = 0.0526, 1097 F2, 35 parameters for the new structure type Sc3Rh1.594(9)In4. In the three structure types the scandium atoms build trigonal prisms. The latter are filled exclusively by palladium atoms in ScPd0.981(2)In, while transition metal and indium atoms fill these sites in the other three structures. The different coloring of the trigonal prismatic sites leads to a symmetry reduction for the structures of Sc3Ni2.10(5)In3.76(5), Sc3Ni2.14(2)In3.76(2) and Sc3Rh1.594(9)In4. The structural relationship is described on the basis of a group-subgroup scheme. Chemical bonding in these intermetallics is briefly discussed.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The indium-rich intermetallic compounds YbCoIn5 and YbRhIn5 were prepared from the elements in sealed tantalum tubes by the indium flux technique with a starting composition 1:1:7. The tubes were heated at 1320 K (YbCoIn5) and 1300 K (YbRhIn5) for six hours followed by slow cooling (5 K/h) to 670 K. YbPtIn4 was prepared in a sealed molybdenum crucible from an arc-melted precursor alloy YbPtIn2 with additional indium (6 h at 1370 K followed by slow cooling at a rate of 5 K/h). The structures of the three indides were investigated by single crystal X-ray data: P4/mmm, HoCoGa5 type, a = 455.90(7), c = 743.3(1) pm, wR2 = 0.0487, 173 F-2 values for YbCoIn5, a = 459.52(6), c = 744.2(2) pm, wR2 = 0.0803, 238 F-2 values for YbRhIn5 with 12 variables per refinement, and Cmcm, YNiAl4 type, a = 444.5(1), b = 1655.0(1), c = 751.6(1) pm, wR2 = 0.1036, 482 F-2 values, 24 variables for YbPtIn4. The transition metal atoms in YbCoIn5 and YbRhIn5 have eight indium neighbors in a square prismatic coordination by indium atoms. These prisms are condensed via common edges forming layers. The ytterbium and further indium atoms are located between these layers. The ytterbium atoms are cuboctahedrally coordinated by twelve indium atoms. The cell volumes indicate intermediate-valent or divalent ytterbium for YbCoIn5 and YbRhIn5. The YbPtIn4 structure consists of a three-dimensional [PtIn4] network in which the ytterbium atoms are located in distorted hexagonal channels. Common structural motifs of the three structures are distorted hcc-like indium cubes which resemble the structure of elemental indium.

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 similar toSmPd(3)In(6) 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 Xray 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, beta = 133.43(2)degrees, wR2 = 0.0681, 1678 F-2 values for La4Pd10In21, a = 2308.2(1), b = 452.52(4), c = 1944.80(9) pm, beta = 133.40(1)degrees, wR2 = 0.0659, 1684 F-2 values for Ce4Pd10In21, a = 2303.8(2), b = 450.78(4), c = 1940.6(1) pm, beta = 133.39(1)degrees, wR2 = 0.0513, 1648 F-2 values for Pr4Pd10In21, a = 2300.2(2), b = 449.75(6), c = 1937.8(2) pm, beta = 133.32(1), wR2 = 0.1086, 1506 F-2 values for Nd4Pd10In21, and a = 2295.6(2), b = 447.07(4), c = 1935.7(1) pm, beta = 133.16(1)degrees, wR2 = 0.2291, 2350 F-2 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.

Single crystals of Eu2PdSi3 were obtained from an arc-melted sample that was further annealed at 1020 K for seven days in a silica tube. The structure of Eu2PdSi3 was refined from single crystal X-ray diffractometer data: P6/mmm, a = 831.88(12), c = 435.88(9) pm, wR(2) = 0.1175, 265 F-2 values, and 13 variable parameters. It crystallizes with the U2RuSi3 structure, a superstructure of the AlB2 type. The palladium and silicon atoms form a planar two-dimensional [PdSi3] network. The two crystallographically different europium atoms have hexagonal prismatic coordinations Eu1Si(12) and Eu2Pd4Si8. The Pd-Si and Si-Si distances within the [PdSi3] network are 244 and 236 pm, respectively.

The stannide LiAg2Sn was synthesized from the elements by reaction in a sealed tantalum tube in a resistance furnace. LiAg2Sn crystallizes with a ternary ordered version of the cubic BiF3 structure, space group Fm (3) over barm: a=659.2(2) pm, wR2=0.0450, 69 F-2 values, 5 variables. The silver and tin atoms form an antifluorite structure of composition Ag2Sn (285 pm Ag-Sn) in which the lithium atoms fill octahedral voids. Electronic structure calculations reveal weak Ag-Ag and strong Ag-Sn bonding within the Ag2Sn substructure. LiAg2Sn is weakly Pauli paramagnetic and a good metallic conductor. Nevertheless, the modestly small Li-7 Knight shift is consistent with a nearly complete state of lithium ionization. The high local symmetry at the tin site is reflected by the absence of a nuclear electric quadrupolar splitting in the Sn-119 Mossbauer spectra and a small chemical shift anisotropy evident from Sn-119 solid state NMR. Static Li-7 solid state NMR spectra reveals motional narrowing effects above 300 K, consistent with lithium atomic mobility on the kHz timescale.

New indide La1.18Rh3In2 was prepared by reaction of the elements in an arc-melting furnace and subsequent annealing at 870 K for four cheeks. La1.18Rh3In2 was investigated h X-ray diffraction on both powders and single crystals. Its structure was found to be of an incommensurate composite type with two intergrown sub-lattices determined and refined by using single crystal X-ray data and superspace group formalism. An incommensurate intergrowth structure model including twinning, with the superspace groups pairs R:P3m1:11 and P:R3m:11, was found to he the hest model for the refinement and description of this structure, The structure refinement resulted in freighted R-values of 0.046 total the total structure factors including both basic and satellite reflections, 0.043 for the main reflections belonging to the two basic substructures and 0.054 for the first order satellites. The rhodium atoms form 3.6.3.6 Kagome nets kith Rh-Rh distances ranging from 2.74 to 2.92 Angstrom. The nets are stacked one upon each other and the resulting trigonal prismatic voids are filled with indium atoms at Rh-In distances of 2.64 to 2.77 Angstrom. The rigid three-dimensional [Rh3In2] network has large flexagonal channels which are filled with lanthanum atoms giving the composition La1.18Rh3In2. The lanthanum sub-lattice is ordered in the hexagonal tunnels with a rhombohedral symmetry. The c-axis of the [Rh3In2] lattice is 4.3725(0) Angstrom while it is 3.695(3) Angstrom for the lanthanum lattice. This mismatch clearly shoals the incommensurability of the structure. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.