Rolf-Dieter Hoffmann

Syntheses and Crystal Structures of CaCuGe, CaAuIn, and CaAuSn – Three Different Superstructures of the KHg2 Type

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. Synthesen und Kristallstrukturen von CaCuGe, CaAuIn und CaAuSn – Drei unterschiedliche Uberstrukturen des KHg2-Typs Die intermetallischen Verbindungen CaCuGe, CaAuIn und CaAuSn konnen aus den Elementen in verschweisten Tantalrohren oder in Glaskohlenstofftiegeln im Hochfrequenzofen hergestellt werden. Ihre Kristallstrukturen wurden anhand von Einkristall-Rontgen-Diffraktometerdaten verfeinert. Die drei Verbindungen kristallisieren mit der gleichen Unterzelle (KHg2-Typ), sie bilden jedoch drei klar unterscheidbare Uberstrukturen in den Raumgruppen Pnma mit unterschiedlichen Elementarzellen aus: a = 2124,9(6) pm; b = 436,0(2) pm; c = 749,4(5) pm; Z = 12; wR2 = 0,0789; 1303 F2-Werte; 56 Variable fur CaCuGe (eigener Strukturtyp); a = 738,2(1) pm; b = 459,4(1) pm; c = 839,4(2) pm; Z = 4; wR2 = 0,0651; 656 F2-Werte; 20 Variable fur CaAuIn (TiNiSi-Typ); a = 3690,3(3) pm; b = 470,5(1) pm; c = 813,6(2) pm; Z = 20; wR2 = 0,1294; 1730 F2-Werte; 92 Variable fur CaAuSn (neuer Strukturtyp). Die drei Strukturen konnen als Uberstrukturen des KHg2-Typs mit einer geordneten Verteilung der Ubergangsmetall- und Germanium (Indium, Zinn)-atome auf den Quecksilberpositionen betrachtet werden. Jedes Calciumatom in den Strukturen von CaCuGe, CaAuIn und CaAuSn hat eine geordnete Umgebung von sechs Ubergangsmetall- und sechs Hauptgruppenelementatomen, welche jeweils in Form zweier gegeneinander verkippter Sechsringe um die Calciumatome angeordnet sind. Alle bisher bekannten Uberstrukturen des KHg2-Typs werden mit Hilfe eines Gruppe-Untergruppe-Schemas beschrieben.

The stannides YbPtSn and Yb2Pt3Sn5

YbPtSn and Yb 2 Pt 3 Sn 5 were prepared from the elements in scaled tantalum tubes in a high-frequency furnace in a novel water-cooled sample chamber. Both structures were refined from single-crystal X-ray data: YbPtSn (ZrNiAl type structure), space group P62m, a = 737.8(3) pm, c = 393.1(2) pm, wR2 = 0.0363, 412 F 2 values, 14 variables; Yb 2 Pt 3 Sn 5 (new structure type), space group Pnma, a = 729.5(2) pm, b 442.2(1) pm, c = 2625.2(6) pm, wR2 = 0.0373. 1378 F 2 values, 62 variables. The structure of YbPtSn contains two crystallographically different platinum positions. Both of them have tricapped trigonal prismatic coordination: [Pt 1 Sn 6 Yb 3 ] and [Pt 2 Sn 3 Yb 6 ]. Yb 2 Pt 3 Sn 5 shows a close relation to the Y 2 Rh 3 Sn 5 structure (space group Cmc2 1 ), however, with a different ordering of the platinum and tin atoms. Both ytterbium positions in Yb 2 Pt 3 Sn 5 have the high co-ordination numbers (CN) of 20 for Yb1 and 18 for Yb2. Magnetic susceptibility measurements of Yb 2 Pt 3 Sn 5 show Curie-Weiss behavior between 50 K and room temperature with an experimental magnetic moment of 2.6(1) μ B /Yb, indicating mixed valency for the ytterbium atoms. Yb 2 Pt 3 Sn 5 is a metallic conductor. 119 Sn Mossbauer spectroscopic data show one signal at δ = 1.75(1 ) mm/s for YbPtSn and δ= 2.02( 1) mm/s for Yb 2 Pt 3 Sn 5 . Both spectra are subjected to quadrupole splitting of ΔE q = 0.59(5) mm/s (YbPtSn) and ΔE q = 0.80(2) mm/s (Yb 2 Pt 3 Sn 5 ).

Structural chemistry of superconducting pnictides and pnictide oxides with layered structures

Abstract The basic structural chemistry of superconducting pnictides and pnictide oxides is reviewed. Crystal chemical details of selected compounds and group subgroup schemes are discussed with respect to phase transitions upon charge-density formation, the ordering of vacancies, or the ordered displacements of oxygen atoms. Furthermore, the influences of doping and solid solutions on the valence electron concentration are discussed in order to highlight the structural and electronic flexibility of these materials.

Rare earth–transition metal–indides

Publisher Summary This chapter reviews the synthesis techniques and the crystal chemistry of rare earth-transition metal-indides. It focuses on the phase relations and physical properties, and discusses the structure-property relationships. The crystal chemistry and chemical bonding of the R – T in compounds strongly depend on the composition. The rare earth metal-rich compounds exhibit typical intermetallic structures with relatively large coordination numbers, as found in close packed arrangements. The ternary rare earth metal-transition metal-indium systems contain a vast number of individual intermetallic compounds. The crystallographic data (lattice parameters) of all known indides is discussed in the chapter. The compounds are grouped with respect to the d element component. The chemical and various physical properties of rare earth-transition metal-indides are discussed in this chapter. Most of these indides are light gray in polycrystalline form. Single crystals have metallic luster. Although the rare earth metals are relatively electropositive elements similar to the alkaline earth metals, there is a significant difference in the stability of the ternary compounds.

Distortedbcc Indium Cubes as Structural Motifs in Ca[TIn4] (T=Rh, Pd, Ir)

: The title compounds were prepared from the elements by reactions in water-cooled glassy carbon crucibles under an argon atmosphere in a high-frequency furnace. CaPdIn4 crystallizes with the YNiAl4-type structure: Cmcm, a=446.7(3), b=1665(1), c=754.3(5) pm, wR2=0.0465 with 646 F2 values and 24 variables. The structure is built up from a complex three-dimensional [PdIn4] polyanion in which the calcium atoms occupy distorted pentagonal tubes formed by indium and palladium atoms. CaRhIn4 and CaIrIn4 adopt the LaCoAl4-type structure: Pmma, a=867.6(1), b=422.91(8), c=745.2(1) pm, wR2=0.0583 with 468 F2 values and 24 variables for CaRhIn4; a=869.5(1), b=424.11(6), c=746.4(1) pm, wR2= 0.0614 471 F2 values with 24 variables for CaIrIn4. This structure type, too, has a three-dimensional [RhIn4] polyanion which is related to the structure of binary RhIn3. The calcium atoms fill distorted pentagonal prismatic channels formed by indium atoms. Semi-empirical band structure calculations for Ca-RhIn4 and CaPdIn4 reveal strongly bonding In-In, Rh-In and Pd-In interactions but weaker Ca-Rh, Ca-Pd and Ca-In interactions. CaRhIn4 and Ca-PdIn4 are compared with other indium-rich compounds such as YCoIn5 and Y2CoIn8, and with elemental indium. Common structural motifs of the indium-rich compounds are distorted bcc-like indium cubes.

The Binary Silicides Eu5Si3 and Yb3Si5 – Synthesis, Crystal Structure, and Chemical Bonding

The binary silicides Eu5Si3 and Yb3Si5 were prepared from the elements in sealed tantalum tubes and their crystal structures were determined from single crystal X-ray data: I4/mcm, a = 791.88(7) pm, c = 1532.2(2) pm, Z = 4, wR2 = 0.0545, 600 F2 values, 16 variables for Eu5Si3 (Cr5B3-type) and P62m, a = 650.8(2) pm, c = 409.2(1) pm, Z = 1, wR2 = 0.0427, 375 F2 values, 12 variables for Yb3Si5 (Th3Pd5 type). The new silicide Eu5Si3 contains isolated silicon atoms and silicon pairs with a Si–Si distance of 242.4 pm. This silicide may be described as a Zintl phase with the formula [5 Eu2+]10+[Si]4–[Si2]6–. The silicon atoms in Yb3Si5 form a two-dimensional planar network with two-connected and three-connected silicon atoms. According to the Zintl-Klemm concept the formula of homogeneous mixed-valent Yb3Si5 may to a first approximation be written as [3 Yb]8+[2 Si–]2–[3 Si2–]6–. Magnetic susceptibility investigations of Eu5Si3 show Curie-Weiss behaviour above 100 K with a magnetic moment of 7.85(5) μB which is close to the free ion value of 7.94 μB for Eu2+. Chemical bonding in Eu5Si3 and Yb3Si5 was investigated by semi-empirical band structure calculations using an extended Huckel hamiltonian. The strongest bonding interactions are found for the Si–Si contacts followed by Eu–Si and Yb–Si, respectively. The main bonding characteristics in Eu5Si3 are antibonding Si12-π* and bonding Eu–Si1 states at the Fermi level. The same holds true for the silicon polyanion in Yb3Si5. Die binaren Silicide Eu5Si3 und Yb3Si5 – Synthese, Kristallstruktur und chemische Bindung Die binaren Silicide Eu5Si3 und Yb3Si5 wurden aus den Elementen in verschweisten Tantalrohren synthetisiert und ihre Kristallstrukturen anhand von Vierkreis-Diffraktometerdaten verfeinert: I4/mcm; a = 791,88(7) pm; c = 1532,2(2) pm; Z = 4; wR2 = 0,0545; 600 F2-Werte; 16 Variable fur Eu5Si3 (Cr5B3-Typ) und P62m; a = 650,8(2) pm; c = 409,2(1) pm; Z = 1; wR2 = 0,0427; 375 F2-Werte; 12 Variable fur Yb3Si5 (Th3Pd5-Typ). Das neue Silicid Eu5Si3 enthalt isolierte Siliciumatome neben Si2 Paaren mit einem Si–Si Abstand von 242,4 pm. Dieses Silicid kann als Zintl Phase mit der Formel [5 Eu2+]10+[Si]4–[Si2]6– geschrieben werden. Die Siliciumatome in Yb3Si5 bilden ein zweidimensionales Netzwerk mit zwei- und dreibindigen Siliciumatomen. In Einklang mit dem Zintl-Klemm Konzept kann die Formel fur das gemischt-valente Silicid Yb3Si5 in erster Naherung als [3 Yb]8+[2 Si–]2–[3 Si2–]6– geschrieben werden. Magnetische Untersuchungen an Eu5Si3 zeigen Curie-Weiss Verhalten oberhalb von 100 K mit einem magnetischen Moment von 7,85(5) μB, welches nahe am freien Ionenwert von 7,94 μB fur Eu2+ liegt. Die chemische Bindung in Eu5Si3 und Yb3Si5 wurde uber semi-empirische Bandstrukturrechnungen nach der extended Huckel Methode untersucht. Diese Rechnungen zeigten, das die Si–Si Wechselwirkungen am starksten sind, gefolgt von den Eu–Si- bzw. Yb–Si-Wechselwirkungen. Die wesentlichen Bindungscharakeristika in Eu5Si3 sind antibindende Si12-π* und bindende Eu–Si1 Zustande an der Fermikante. Dies gilt auch fur das Siliciumpolyanion in Yb3Si5.

STRUCTURE, CHEMICAL BONDING, AND PROPERTIES OF COIN3, RHIN3, AND IRIN3

CoIn3, RhIn3, and IrIn3 were synthesized by reacting the elements in sealed tantalum tubes at 1170 K and subsequent annealing at 770 K. The structures of the three compounds (FeGa3 type, space group P42/mnm) were refined from single crystal X-ray data: a = 682.82(6), c = 709.08(7) pm, wR2 = 0.0407, 397 F2 values for CoIn3, a = 698.28(8), c = 711.11(9) pm, wR2 = 0.0592, 418 F2 values for RhIn3, and a = 699.33(5), c = 719.08(5) pm, wR2 = 0.0625, 482 F2 values for IrIn3 with 16 parameters for each refinement. The structures may be considered as an intergrowth of tungsten-like building blocks of indium atoms and AlB2-like slabs of compositions In&Co, In&Rh, and In&Ir, respectively. These are compared with the related intergrowth variants found for compounds with ordered U3Si2 and Zr3Al2 type structure. Semi-empirical band structure calculations for RhIn3 reveal low density-of-states (DOS) at the Fermi level and negative Rh–Rh crystal orbital overlap populations (COOP) indicating antibonding Rh–Rh interactions. The bonding characteristics of CoIn3, RuIn3, and IrIn3 are similar to RhIn3. Magnetic susceptibility measurements of compact polycrystalline samples of CoIn3, RhIn3, and IrIn3 indicate weak Pauli paramagnetism. Struktur, Chemische Bindung und Eigenschaften von CoIn3, RhIn3 und IrIn3 CoIn3, RhIn3 und IrIn3 wurden durch Reaktion der Elemente bei 1170 K in verschweisten Tantalampullen und anschliesendes Tempern bei 770 K synthetisiert. Die Kristallstrukturen der drei Verbindungen (FeGa3-Typ, Raumgruppe P42/mnm) wurden anhand von Einkristall-Diffraktometer-Daten verfeinert: a = 682,82(6); c = 709,08(7) pm; wR2 = 0,0407; 397 F2-Werte fur CoIn3; a = 698,28(8); c = 711,11(9) pm; wR2 = 0,0592; 418 F2-Werte fur RhIn3 und a = 699,33(5); c = 719,08(5) pm; wR2 = 0,0625; 482 F2-Werte fur IrIn3 mit jeweils 16 Parametern. Die Strukturen konnen als Verwachsungsvarianten von Wolfram-ahnlichen Baueinheiten aus Indiumatomen und AlB2-ahnlichen Baueinheiten der Zusammensetzungen In&Co, In&Rh, und In&Ir beschrieben werden. Diese werden mit den sehr ahnlichen Verwachsungsvarianten von Verbindungen mit geordneter U3Si2- und Zr3Al2-Struktur verglichen. Semi-empirische Bandstrukturrechnungen fur RhIn3 zeigen eine niedrige Zustandsdichte (DOS) an der Fermikante sowie negative Rh–Rh Kristall-Orbital-Uberlappungspopulationen (COOP), was auf antibindende Rh–Rh-Wechselwirkungen hindeutet. Die Bindungscharakteristiken fur CoIn3, RuIn3 und IrIn3 sind ahnlich. Magnetische Suszeptibilitatsmessungen an kompakten, polykristallinen Proben von CoIn3, RhIn3 und IrIn3 ergeben schwachen Pauli-Paramagnetismus.

Intermetallic rare earth (RE) magnesium compounds REPdMg and RE2Pd2Mg

Abstract The intermetallic rare earth metal compounds REPdMg (RE=Nd, Eu, Tb, Ho, Tm, Yb) and RE2Pd2Mg (RE=Y, Pr, Nd, Sm, Gd, Tb, Dy, Ho) were synthesized from the elements by reactions in sealed tantalum tubes in a high-frequency furnace. All compounds were investigated by X-ray powder diffraction. With a trivalent rare earth element, the REPdMg intermetallics adopt the hexagonal ZrNiAl structure, while those with a divalent rare earth metal crystallize with the orthorhombic TiNiSi type. The structures of EuPdMg and YbPdMg have been refined on the basis of single-crystal diffractometer data: Pnma, a=753.85(9), b=440.27(4), c=866.27(9) pm, wR2=0.0770, 366 Fo2 values, 20 variables for EuPdMg and a=729.4(2), b=424.3(2), c=850.5(3) pm, wR2=0.0622, 546 Fo2 values, 20 variables for YbPdMg. In both structure types, the palladium and magnesium atoms build a three-dimensional [PdMg] network in which the rare earth metal atoms fill distorted hexagonal channels. With a lower magnesium content the compounds RE2Pd2Mg with the tetragonal Mo2FeB2 structure, space group P4/mbm were obtained. Single crystal data yielded a=774.4(2), c=393.37(8) pm, wR2=0.0556, 216 Fo2 values, 13 variables for Nd2Pd2Mg and a=762.56(8), c=380.55(7) pm, wR2=0.0476, 298 Fo2 values, 12 variables for Tb2Pd2Mg. The magnesium position of the neodymium compound shows a small magnesium/palladium mixed occupancy leading to the refined composition Nd2Pd2.11Mg0.89. The compounds may be considered as intergrowths of CsCl and AlB2 related slabs of compositions REMg and REPd2. The crystal chemistry and chemical bonding in these intermetallics is briefly discussed. The magnetic properties of YbPdMg, Pr2Pd2Mg and Sm2Pd2Mg were investigated with a SQUID magnetometer. YbPdMg is Pauli paramagnetic with a room temperature susceptibility of 246(5)×10−6 cm3/mol. Pr2Pd2Mg is Curie–Weiss paramagnetic above 100 K with an experimental magnetic moment of 3.86(5) μB/Pr atom. Antiferromagnetic ordering occurs at 15(1) K. Pr2Pd2Mg is a metamagnet with a critical field of 0.8(1) T. The saturation magnetization at 2 K and 5 T is 2.65(5) μB/Pr atom. Sm2Pd2Mg shows Van Vleck paramagnetism.

Two-dimensional [TIn2] polyanions in BaTIn2 (T=Rh, Pd, Ir, Pt)--the collapse of the three-dimensional indium polyanion of BaIn2.

The title compounds were prepared from the elements by reactions in sealed tantalum tubes in a high-frequency furnace. The four compounds were investigated by X-ray diffraction both on powders and single crystals, and the structures of the rhodium and platinum compounds were refined from single-crystal data: Cmcm, a = 447.68(8), b = 1131.1(2), c = 805.6(2) pm, wR2 = 0.0561, 354 F2 values for BaRhIn2; a = 452.06(8), b = 1162.4(2). c = 801.5(1) pm, wR2 = 0.1427, 362 F2 values, for BaPtIn2: with 16 variables for each refinement. The structures are isopointal to MgCuAl2 and can be considered to be a transition metal (T) filled CaIn2 type, in which the indium atoms form a distorted network like hexagonal diamond (lonsdaleite). The indium substructure is cut apart in BaTIn2 and resembles together with the transition metal atoms a two-dimensional polyanion rather than a three-dimensional polyanion as found in the compounds CaTIn2, CaTSn2, and SrTIn2. Semiempirical band structure calculations support the assumption of a two-dimensional polyanion in which the strongest interactions are found for the T-In contacts.

CaRhIn with TiNiSi Type Structure and CaTIn2 (T = Rh, Ir) with a New Filled Version of the Zintl Phase CaIn2

CaRhIn, CaRhIn2, and CaIrIn2 were synthesized by reacting the elements in glassy carbon crucibles under an argon atmosphere in a high-frequency furnace. CaRhIn adopts the TiNiSi structure: Pnma, a = 730.0(4) pm, b = 433.1(2) pm, c = 828.8(4) pm, wR2 = 0.0707, 630 F2 values, 20 variables. The CaRhIn structure consists of strongly puckered Rh3In3 hexagons with Rh–In distances ranging from 273 to 276 pm. Due to the strong puckering each rhodium atom has a distorted tetrahedral indium environment. The calcium atoms fill the channels within the three-dimensional [RhIn] polyanion. CaRhIn2 and CaIrIn2 crystallize with a new structure type: Pnma, a = 1586.2(3) pm, b = 781.4(2) pm, c = 570.9(1) pm, wR2 = 0.0385, 1699 F2 values, 44 variables for CaRhIn2, and Pnma, a = 1588.7(3) pm, b = 780.8(1) pm, c = 574.0(1) pm, wR2 = 0.0475, 1661 F2 values, 44 variables for CaIrIn2. The structures of CaRhIn2 and CaIrIn2 can be described as an orthorhombically distorted rhodium respectively iridium filled CaIn2. The motif of transition metal filling is similar to that found in MgCuAl2 type compounds CaTIn2 (T = Pd, Pt, Au) and SrTIn2 (T = Rh, Pd, Ir, Pt), but constitute a different tiling. Semi-empirical band structure calculations for CaRhIn and CaRhIn2 reveal strong bonding In–In and Rh–In but weaker Ca–Rh and Ca–In interactions. Magnetic susceptibility and resistivity measurements of compact polycrystalline samples of CaRhIn2 indicate weak Pauli paramagnetism and metallic conductivity with a room temperature value for the specific resistivity of 230 ± 50 μΩcm.