Ternäre Palladiumpnictide der Erdalkali- und Seltenen Erdmetalle mit ThCr2Si2- und CaBe2Ge2-Struktur

Fifteen compounds of compositionMPd₂ Pn ₂ (M = alkaline earth or rare earth metal,Pn = As, Sb, Bi) were prepared. TheirGuinier powder patterns show that the arsenides crystallize with the ThCr₂Si₂ type structure, the bismuthides with the closely related CaBe₂Ge₂ type structure. The antimonides most likely also have the CaBe₂Ge₂ structure as is demonstrated by a structure refinement of EuPd₂Sb₂ from single crystal X ray data (R = 0.039 for 366 independent structure factors and 15 variable parameters). The structure of SrPd₂As₂ (ThCr₂Si₂ type) was refined to a residual ofR = 0.020 for 182F values and 9 variables. EuPd₂Sb₂ is paramagnetic and a metallic conductor. A comparison of the cell volumes suggests intermediate valency for Eu in EuPd₂As₂.Chemical bonding and especially the reasons for the adoption of the ThCr₂Si₂ or CaBe₂Ge₂ type structures by these compounds are discussed. It is suggested that in going from the phosphides to the bismuthides the ThCr₂Si₂ structure is loosing and the CaBe₂Ge₂ structure is gaining stability due to decreasing Pd-Pd bonding and increasing Pd-pnictogen bonding. This trend is caused by the increasing size of the pnictogen component.

     

Neue AB2X2-Verbindungen mit CaBe2Ge2-Struktur

New AB₂X₂ Compounds with CaBe₂Ge₂ Structure Crystal structure of ternary RELi₂Sb₂ compounds (RE = Ce, Pr, Nd) is reported. The compounds are isotypic and crystallize tetragonally in the CaBe₂Ge₂ structure (space group P4/nmm), which is a modified type of the ThCr₂Si₂ structure.     

Polymorphie bei APd2X2-Verbindungen (A = Sr,Ba; X = As,Sb)

Polymorphism of APd₂X₂-Compounds (A = Sr, Ba; X = As, Sb) SrPd₂Sb₂ crystallizes at room temperature in the CaBe₂Ge₂-type structure (lattice constants see “Inhaltsübersicht”); a high-temperature modification with ThCr₂Si₂-type structure was obtained by quenching samples from above 730°C. The same structure was found for the high-temperature modification of BaPd₂As₂ which can be prepared by quenching from above 720°C. For (ThCr₂Si₂-structure) no phase transition could be observed.     

ACu9X4 ‐ Neue Verbindungen mit der CeNi8, 5Si4, 5‐Struktur (A: Sr,Ba; X: Si,Ge)

ACu₉X₄ ‐ New Compounds with CeNi_{8, 5}Si_{4, 5} Structure (A: Sr, Ba; X: Si, Ge) The new compounds SrCu₉Si₄ (a = 8.146(1), c = 11.629(2)Å), BaCu₉Si₄ (a = 8.198(2), c = 11.735(2)Å), SrCu₉Ge₄ (a = 8.273(2), c = 11.909(5)Å), and BaCu₉Ge₄ (a = 8.338(4), c = 12.011(7)Å) are formed by reaction of the elements at 1000° ‐ 1100 °C. They are isotypic (I4/mcm, Z = 4) and crystallize in an ordered variant of the cubic NaZn₁₃ type structure, also built up by the binary phase BaCu₁₃. In the ternary compounds the positions of Cu2 are orderly occupied by copper and silicon and germanium, respectively. This results in a lowering of symmetry and a distortion of the polyhedra. The metallic conductivity of the compounds was confirmed by measurements on BaCu₉Si₄.     

Zur Polymorphie von SrNi2P2 sowie zur Kristallstruktur von BaNi2P2

About Polymorphism of SrNi₂P₂ and Crystal Structure of BaNi₂P₂ SrNi₂P₂ and BaNi₂P₂ were prepared by heating mixtures of the elements and investigated by single crystal X-ray methods. The Sr compound at room temperature crystallizes in a superstructure of the ThCr₂Si₂ type (NT-phase; Immm; Z = 6; a = 3.951(2), b = 11.853(2), c = 10.432(2) Å), which is caused by displacements of the atoms from the ideal positions; the P? P distances are 2.45 and 3.28 Å. With increasing temperature at 45°C (ambient pressure) and increasing pressure at 4 kbar (room temperature) respectively the compound undergoes first order phase transitions and crystallizes after that in the undistorted ThCr₂Si₂ type (I4/mmm; Z = 2). While the P atoms of the high temperature phase (HT-SrNi₂P₂: a = 3.948(1), c = 10.677(3) Å; 100°C) are isolated from each other (d_{p p}: 3.12 Å) they most probably form pairs in the high pressure phase (HD-SrNi₂P₂: a = 4.003(1), c = 9.761(2) Å; ca. 4 kbar). This will be discussed on the basis of band structure calculations. BaNi₂P₂ (a = 3.947(1), c = 11.820(1) Å) also crystallizes in the ThCr₂Si₂ type structure, the P? P distance is extended to 3.71 Å.     

Über LaCo2P2 und andere Neue Verbindungen mit ThCr2Si2- und CaBe2Ge2-Struktur

On LaCo₂P₂ and Other New Compounds with ThCr₂Si₂- and CaBe₂Ge₂-Type Structure The compounds MCo₂P₂ (M = La, Ce, Pr, Nd, Sm, Th, U), MFe₂P₂ (M = La, Ce, U), and ThCo₂As₂ were prepared for the first time. Structure determinations from single crystal X-ray data of LaCo₂P₂ (R = 0.011; 325 F-values), CeCo₂P₂ (R = 0.023; 160 F), PrCo₂P₂ (R = 0.044; 441 F), LaFe₂P₂ (R = 0.024; 511 F), and CeFe₂P₂ (R = 0.016; 183 F) with 11 variable parameters each resulted in atomic positions within the range of the ThCr₂Si₂-type. The powder patterns of ThCo₂P₂, and ThCo₂As₂ show superstructure reflections indicating a CaBe₂Ge₂-type structure. The other compounds can be assigned to the ThCr₂Si₂-type. Chemical bonding of these can be rationalized by a simple band structure model where bonding transition metal – transition metal interactions are important.     

Neue ternäre Verbindungen des Caesiums mit Elementen der 8. Nebengruppe und 5. Hauptgruppe

New Ternary Compounds of Cesium and Elements of the 8^th Transition Metal Group and the 5^th Main Group In the ternary systems Cesium/element of the 8^th transition metal group/element of the 5^th main group some new compounds were found and investigated. Compounds of the formula Cs₂MX₂ (M = Pt, Pd, Ni; X = P, Sb, Bi) can be placed in a line with the K₂PdP₂-type structure. The new compound with the formula CsFe₂Sb₂ crystallizes in the ThCr₂Si₂-type structure. By single crystal measurements CsFe₂As₂ was found to crystallize in the space group I4/mmm with the lattice constants a = 389.43 pm and c = 1 509.97 pm.     

Synthese und Kristallstrukturen der Calcium‐Iridiumsilicide Ca3Ir4Si4 und Ca2Ir2Si

Synthesis and Crystal Structures of the Calcium Iridium Silicides Ca₃Ir₄Si₄ and Ca₂Ir₂Si The new compounds Ca₃Ir₄Si₄ und Ca₂Ir₂Si were prepared by reaction of the elemental components in sealed tantalum ampoules at 1200 °C. Their structures were determined from X‐ray single crystal data. Ca₃Ir₄Si₄(cubic, space group I4¯3m, a = 7.4171(2)Å, Z = 2) crystallizes with the Na₃Pt₄Ge₄ type structure. For Ca₂Ir₂Si (monoclinic, space group C2/c, a = 9.6567(5)Å, b = 5.8252(2)Å, c = 7.3019(4)Å, β = 100.212(2)°, Z = 4) a new structure was found. Chains of edge sharing, heavily distorted SiIr₄‐tetrahedra (Ir‐Si: 2.381 and 2.414Å) are connected via short Ir—Ir‐contacts (2.640Å) to form an open Ir/Si‐framework accommodating a three‐dimensional arrangement of calcium atoms (Ca—Ca: 3.413 ‐ 3.948Å).     

Zur Kenntnis eines Barium-Kupfer-Orthoarsenats: BaCu2(AsO4)2

On the Crystal Structure of Barium-Copper-Orthoarsenate BaCu₂(AsO₄)₂ Single crystals of BaCu₂(AsO₄)₂ were prepared above 1 000°C by CO₂-LASER technique and investigated by X-ray structure determination. The light blue crystals show monoclinic symmetry, space group C? P2₁/n, a = 4.752; b = 8.506; c = 8.945 Å; β = 93.49°, Z = 2. BaCu₂(AsO₄)₂ represents a hitherto unknown structure type with Cu²⁺ in trigonal bipyramidal coordination. Ba²⁺ shows an 8 + 2 surrounding by O^2? and As⁵⁺ is tetrahedrally coordinated. The crystal structure is discussed with respect to related orthophosphates and vanadates.     

Neue ternäre Rhodium‐ und Iridium‐Phosphide und ‐Arsenide mit U4Re7Si6‐Struktur

New Ternary Rhodium‐ and Iridium‐Phosphides and ‐Arsenides with U₄Re₇Si₆ Type Structure Single crystals of Mg₄Rh₇P₆ (a = 7.841(1) Å), Mg₄Rh₇As₆ (a = 8.066(1) Å), Yb₄Rh₇As₆ (a = 8.254(1) Å) and Mg₄Ir₇As₆ (a = 8.082(2) Å) were prepared by heating mixtures of the elements in a lead flux and were investigated by means of X‐ray methods. The compounds are isotypic and they crystallize in the U₄Re₇Si₆ type structure (Im 3 m; Z = 2), which is formed by CeMg₂Si₂ analogous units, which are twisted against each other. The Rh(Ir) atoms building these units are coordinated tetrahedrally by the non‐metal. The P(As) atoms of six units form a regular octahedron, which is centred by an additional Rh(Ir) atom. This second structural segment corresponds to the perovskit type structure.     

Neue ternäre Phosphide und Arsenide mit einem Metall : Nichtmetall‐Verhältnis im Bereich von 2 : 1

New Ternary Phosphides and Arsenides with a Metal : Non‐Metal Ratio in the Range of 2 : 1 Six new compounds were prepared by heating mixtures of the elements or by reaction of them in a tin(lead) flux. They were investigated by single crystal X‐ray methods. Sc₂Ni₁₂P₇ (a = 9.013(1), c = 3.590(1) Å) crystallizes in the Zr₂Fe₁₂P₇ type structure (P6; Z = 1), which is basically built up likewise by Eu₂Pd₁₂As₇ (a = 10.040(1), c = 4.100(1) Å) and Sr₂Rh₁₂P₇ (a = 9.626(1), c = 3.844(1) Å), but one of seven non‐metal atoms has a somewhat modified environment and is disordered along [001]. Therefore their crystal structure corresponds to the Ho₂Rh₁₂As₇ type structure (P6₃/m; Z = 1). Ca₂Ni₇P₄ (a = 3.703(1), b = 9.209(1), c = 10.378(1) Å) forms the Nd₂Ni₇P₄ type structure (Pmn2₁; Z = 2), whereas the atomic arrangements of Ca₄Rh₁₃As₉ (a = 3.903(2), b = 11.221(1), c = 19.411(4) Å) and Sm₄Rh₁₃As₉ (a = 3.913(2), b = 11.242(6), c = 19.440(6) Å) correspond basically to the Ho₄Ir₁₃Ge₉ type structure (Pmmn; Z = 2), but the disorder of Rh8 required the occupation of splitting positions. The transition metals have three, four or five neighbouring atoms of phosphorus or arsenic and form together with them three‐dimensional covalent frameworks, of which holes are occupied by the atoms of the electropositive metal. Most of the polyhedra around the P and As atoms respectively consist of trigonal prisms of metal atoms with additional metal atoms capping the rectangular faces of the prisms. This environment ist characteristic for ternary phosphides and arsenides with a metal : non‐metal ratio in the range of 2 : 1.     

Über den Einfluß von Temperatur,Druck und Substitution auf die Kristallstruktur von ARh2P2 (A = Ca,Sr, Eu,Ba)

About the Effect of Temperature, Pressure, and Substitution on the Crystal Structure of ARh₂P₂ (A = Ca, Sr, Eu, Ba) Four compounds ARh₂P₂ (A = Ca, Sr, Eu, Ba) were prepared by heating mixtures of the elements and investigated by means of single crystal X-ray methods. They crystallize in the ThCr₂Si₂ type structure (I4/mmm; Z = 2) with P? P distances along [001] reaching from 2.26 Å (CaRh₂P₂) to 3.74 Å (BaRh₂P₂). With increasing temperature (EuRh₂P₂) or increasing pressure (SrRh₂P₂) a first order phase transition occurs with strong changes of the P? P distances. Substitution of the atoms changes the bond lengths of the compounds too.     

Synthese und Kristallstruktur von Sr2Rh7P6

Synthesis and Crystal Structure of Sr₂Rh₇P₆ Single crystals of Sr₂Rh₇P₆ were obtained by reaction of the elements in molten lead at 1100 °C and investigated by X-ray methods. The compound crystallizes tetragonally (a = 11.080(2), c = 4.098(1) Å) and forms a crystal structure (P 4 2₁m; Z = 2) with ThCr₂Si₂ analogous units, which are linked with each other in a new way. Therefore the RhP₄ tetrahedra form bands of edge sharing chains parallel to [001] anstead of layers as in the ThCr₂Si₂ type structure. The arrangement enables a part of the P atoms to form short P–P distances of 2,26 Å and space for additional Rh atoms with a likewise distorted tetrahedral coordination of P atoms is obtained.     

Darstellung und Kristallstruktur neuer AM2X2-Verbindungen in den Systemen Erdalkalimetall-Platinmetall-Germanium

Preparation and Crystal Structure of New AM₂X₂ Compounds in the Systems Earthalkali Metal/Platinum Metal/Germanium . Four new ternary compounds in the systems earthalkali metal/platinum metal/germanium have been prepared and characterised by single crystal X-ray investigation. BaRu₂Ge₂ crystallizes orthorhombically, space group Fddd, a=634.4(1) pm, b=1 056.5(3) pm, c=1 273,1(3) pm. SrRu₂Ge₂ (a=430.6(1) pm, c=1 030.3(2) pm), BaRh₂Ge₂ (a=418.9(5) pm, c=1 175.7(10) pm) and SrRh₂Ge₂ (a=418.3(3) pm, c=1 071.8(6) pm) crystallize in the ThCr₂Si₂-type structure (tetragonal, space group I4/mmm).     

Kristall‐ und elektronische Strukturen von AIr2P2 (A: Ca — Ba)

Crystal and Electronic Structures of AIr₂P₂ (A: Ca — Ba) Single crystals of CaIr₂P₂ (a = 6.610(3), c = 7.031(3)Å) were prepared by reaction of the elements in a lead flux and investigated by X‐ray methods. The compound crystallizes with the EuIr₂P₂ type (P3₂21; Z = 3) just detected in the case of SrIr₂P₂. In the structure all the P atoms and half of the Ir atoms build a three‐dimensional framework with Ca and the remaining Ir atoms in the cavities. The latter atoms form threefold screws along [001] with relatively short Ir‐Ir distances and they are connected with the framework by Ir‐P bonds. LMTO band structure calculations suggested that the compounds with Ca, Sr, and Eu should be semiconductors. For EuIr₂P₂ this was confirmed by conductivity measurements. BaIr₂P₂ (a = 3.946(1), c = 12.572(2)Å) synthesized by heating the elements at 1050 °C for a long time crystallizes with the ThCr₂Si₂ type structure (I4/mmm; Z = 2). Due to the rigid layers of IrP₄ tetrahedra and the atomic size of barium the P‐P distance between the layers with a value of 3.71Å is very long.     

Ternäre Nickelphosphide und -arsenide mit einem Metall: Nichtmetall-Verhältnis von 2:1

Ternary Phosphides and Arsenides of Nickel with a Metal: Non-Metal Ratio of 2:1 Several new ternary phosphides and arsenides of nickel were prepared by reaction of the elements. SrNi₅P₃, SrNi₅As₃, and EuNi₅As₃ crystallize in the LaCo₅P₃ structure with the following lattice constants [Å]: BaNi₉P₅ (a = 6.534(1) Å, c = 10.847(2) Å) and BaNi₉As₅ (a = 6.760(1) Å, c = 11.226(2) Å) crystallize in a new type of structure (P6₃/mmc, Z = 2). The characteristic polyhedra are trigonal Ni-antiprisms centered by P or As atoms and trigonal Ni-prisms with vacant centres and sides capped by non-metal atoms. U₂Ni₁₂P₇ (a = 9.077(2) Å, c = 3.694(1) Å) has a Zr₂Fe₁₂P₇ structure (P6 , Z = 1).     

Tt‐Tt (Tt = Si,Ge) Dumb‐Bell Structures at Different Valence Electron Concentrations: Ln2MgSi2 (Ln = La,Ce), Yb2Li0.5Ge2, and Yb1.75Mg0.75Si2

The isostructural compounds Yb₂MgSi₂, La_2.05Mg_0.95Si₂, and Ce_2.05Mg_0.95Si₂, as well as Yb₂Li_0.5Ge₂ and Yb_1.75Mg_0.75Si₂, respectively, were synthesized from stoichiometric mixtures of the corresponding elements in sealed Nb‐ ampoules under argon atmosphere. The structures were determined by single crystal X‐ray diffraction: Yb₂MgSi₂ (P4/mbm (No. 127), a = 7.056(1), c = 4.130(1) ų, Z = 2), La_2.05Mg_0.95Si₂ (P4/mbm, a = 7.544(1), c = 4.464(1) ų, Z = 2), and Ce_2.05Mg_0.95Si₂ (P4/mbm, a = 7.425(1), c = 4.370(1) ų, Z = 2), Yb₂Li_0.5Ge₂ (Pnma (No. 62), a = 7.0601(6), b = 14.628(1), c = 7.6160(7) Å, V = 786.5ų, Z = 4), Yb_1.75Mg_0.75Si₂ (Pnma, a = 6.9796(1), b = 14.4009(1), c = 7.5357(1) Å, V = 757.43(2) ų, Z = 4). All compounds contain exclusively Tt‐Tt dumb‐bells (Tt = Si, Ge). The Si‐Si Zintl anions exhibit only very small variations of bond lengths which seem to be more due to cation matrix effects than to effective bond orders.     

Die Tieftemperaturmodifikationen von Ag6Si2O7 und Ag6Ge2O7 – Darstellung,Kristallstruktur und Vergleich der Ag?Ag-Abstände

On the Low Temperature Modifications of Ag₆Si₂O₇ and Ag₆Ge₂O₇ – Synthesis, Crystal Structure, and Comparison of Ag? Ag Distances For the first time, single crystals of Ag₆Si₂O₇ and Ag₆Ge₂O₇ have been obtained by solid state reactions of the binary oxides at temperatures of 350°C while applying oxygen pressures of 700 bar. According to the results of X-ray crystal structure determinations both compounds crystallize isostructural in P2₁ (Ag₆Si₂O₇: a = 5.3043(5) Å, b = 9.7533(7) Å, c = 15.9283(13) Å, β = 91.165(8)°, 3881 independent reflections, R1 = 3.3%, wR2 = 7.2%; Ag₆Ge₂O₇: a = 5.3713(4) Å, b = 9.9835(8) Å, c = 16.2249(14) Å, β = 90.904(8)°, 2111 independent reflections, R1 = 4.3%, wR2 = 6.0%, Z = 4). The crystal structures contain two independent M₂O₇^6? anions, one in a staggered, and the other in an ecliptic conformation. The cationic partial structure may be described as a distorted bcc arrangement of Ag⁺ and M⁴⁺. Comparison of the structures with respect to the Ag? Ag separations reveals the latter to be probably due to intrinsic d¹⁰–d¹⁰ bonding interactions as far as the range of 2.89 Å to 3.25 Å is considered.     

Neuartige Polyanionen in Zintlphasen. Zur Kenntnis von Ca3Si2As4, Ca3Ge2As4, Sr3Si2As4 und Sr3Ge2As4

New Polyanions in Zintl Phases. On Ca₃Si₂As₄, Ca₃Ge₂As₄, Sr₃Si₂As₄, and Sr₃Ge₂As₄ The new compounds Ca₃Si₂As₄, Ca₃Ge₂As₄, Sr₃Si₂As₄ and Sr₃Ge₂As₄ crystallize in the monoclinic system with lattice constants see “Inhaltsübersicht”. There are two new structure types. Both contain Si₂As₆ or Ge₂As₆ groups connected to chains in different ways. These chains are ordered parallel to each other to sheets with the alkaline-earth atoms between them.     

Synthese und Kristallstruktur von ACu4As2 (A: Ca–Ba,Eu)

Synthesis and Crystal Structure of A Cu₄As₂ ( A : Ca–Ba, Eu) Steel‐gray single crystals of ACu₄As₂ with A = Ca–Ba and Eu respectively were synthesized by heating mixtures of the elements at about 900 °C. Structure determinations with X‐ray diffractometry data revealed, that the isotypic compounds crystallize in the rhombohedral CaCu₄P₂ type structure (R3m; Z = 3) (hexagonal axes see ”︁Inhaltsübersicht”︁”︁). Measurements of the susceptibility of EuCu₄As₂ showed divalent Eu and ferromagnetic order at 35 K.