Na0.74Ta3O6, ein niedervalentes Oxotantalat mit einer Ta–Ta‐Mehrfachbindung

Na_0.74Ta₃O₆, a Low‐Valent Oxotantalate with Multiple Ta–Ta Bonds The title compound was prepared in a sealed tantalum tube through the reaction of Ta₂O₅, tantalum and Na₂CO₃ in a NaCl flux at 1570 K within 5 d. The crystal structure of Na_0.74Ta₃O₆ (a = 713.5(1), b = 1027.4(2), c = 639.9(1) pm, Immm, Z = 4) was determined by single crystal X‐ray means. The structure is isomorphous with NaNb₃O₅F [1]. The characteristic structural units are triply bonded Ta1₂ dumb‐bells with eight square‐prismatically co‐ordinated O ligands. Four Ta2, each octahedrally surrounded by O atoms, are side‐on bonded weakly to the binuclear Ta₂O₈ complex, thus forming a Ta₆ propellane‐like cluster. The lattice parameters of three additional M_xTa₃O₆ phases, M = Li, Mn, and Yb, are reported.     

Synthese,Struktur und Eigenschaften der tantalreichen Silicidchalkogenide Ta15Si2QxTe10–x (Q = S,Se)

Synthesis, Structure, and Properties of the Tantalum‐rich Silicide Chalcogenides Ta₁₅Si₂Q_xTe_10–x (Q = S, Se) The quaternary tantalum silicide chalcogenides Ta₁₅Si₂Q_xTe_10–x (Q = S, Se) are accessible from proper, compacted mixtures of the respective dichalcogenides, silicon and elemental tantalum at 1770 K in sealed molybdenum tubes. The structures were determined from the strongest X‐ray intensities of fibrous crystals with cross sections of about 3 μm and confirmed by fitting the profile of single phase X‐ray diffractograms. The phases Ta₁₅Si₂S_3.5Te_6.5 and Ta₁₅Si₂Se_3.5Te_6.5 crystallize in the monoclinic space group C2/m with two formula units per unit cell, a = 2393.7(1) pm, b = 350.08(2) pm, c = 1601.2(1) pm, β = 124.700(4)°, and a = 2461.3(2) pm, b = 351.70(2) pm, c = 1601.7(1) pm, β = 124.363(5)°, respectively. Tri‐capped trigonal prismatic Ta₉Si clusters stabilized by encapsulated Si atoms can be seen as the characteristic unit of the structure. The clusters are fused into twin columns which are connected by additional Ta atoms, thus forming corrugated layers. The remaining valences at the surfaces of the layered Ta–Si substructure are saturated by those of chalcogen atoms which are coordinated only from one side by three, four or five Ta atoms. Few bridging covalent Ta–S–Ta and Ta–Se–Ta bonds and, otherwise, dispersive interactions between the Q atoms hold these nearly one nanometer wide slabs together. The phases are moderate metallic conductors. There is no evidence for any electronic instability within 10–310 K in spite of the high anisotropy of the structures.     

MAl2Ta35O70 (M = Na,K, Rb), niedervalente Oxotantalate mit isolierten kuboktaedrischen Ta6O12-Clustern

MAl₂Ta₃₅O₇₀ (M = Na, K, Rb), Low-Valent Oxotantalates with Discrete Cuboctahedral Ta₆O₁₂ Clusters The title compounds were prepared by reducing Ta₂O₅ with tantalum and aluminium in the presence of alkali metal carbonates at 1650 K. NaAl₂Ta₃₅O₇₀ was characterized by means of a single crystal X-ray structure determination: space group P 3, lattice parameters a = 780.15(7) pm, c = 2621.7(8) pm, Z = 1, 167 variables, R_F = 0.048. The structure can be described in terms of a close packing of oxide ions with specific defects. The sequence of the layers is hhcchchcchh. The characteristic structural units are Ta₆O₁₂ clusters being substantially stabilized by Ta–Ta bonding (d_Ta–Ta = 279.3–283.3 pm, 14 electrons per cluster). The sodium cations occupy acentrically and statistically half of the anti-cuboctahedral sites. The compounds are semiconductors with band gaps E_a of 0.2 to 0.3 eV.     

Tantalcluster in oxidischer Matrix – Synthese und Strukturen der gemischtvalenten Oxotantalate M2–δTa15O32 (M = K,Rb (δ = 0); M = Sr (δ = 0.15), Ba (δ = 0.12))

Tantalum Cluster in an Oxidic Matrix – Synthesis and Structures of Mixed-Valence Oxotantalates M_2–δTa₁₅O₃₂ (M = K, Rb (δ = 0); M = Sr (δ = 0.15), Ba (δ = 0.12)) The mixed-valent oxides Sr_1.85Ta₁₅O₃₂ ( 1 ), Ba_1.88Ta₁₅O₃₂ ( 2 ), K₂Ta₁₅O₃₂ ( 3 ), Rb₂Ta₁₅O₃₂ ( 4 ) were prepared from appropriate mixtures of Ta₂O₅, tantalum and the corresponding carbonate at 1520–1670 K in sealed tantalum tubes. According to X-ray single crystal structure analyses the oxides crystallize in the space group R3¯, Z = 1. The lattice parameters in the hexagonal setting are a = 777.36(11), c = 3516.2(7) pm for 1 , a = 778.87(11), c = 3548.1(7) pm for 2 , a = 780.7(2), c = 3573.1(11) pm for 3 , and a = 781.90(11), c = 3593.0(7) pm for 4 . The oxide ions form a defect dense packing with the layer sequence chhhh. Anti-cuboctahedral sites are completely occupied by the alkali metal cations. The alkaline earth cations occupy 92 to 94% of such sites; they are displaced from the centres. Smaller voids are located in the centres of the cuboctahedral Ta₆O₁₂ clusters forming the characteristic structural unit of these low-valent oxotantalates. In case of 3 and 4 the clusters have 13 electrons, in case of 1 and 2 they have close to 15 electrons available for Ta–Ta-bonding. Moreover, the structures of the alkali and alkaline earth metal compounds differ notably with respect to the spectrum of Ta–O and Ta–Ta distances in the Ta₃O₁₃ octahedra triples forming another characteristic structural unit for these oxides. Such differences are traced back to distinct local charge balances for the uni- and divalent cations. The oxides 2 , 3 are semiconductors with band gaps ranging from 130 to 360 meV.     

Synthetic,Structural, and Spectroscopic Investigations of K3Nb8O21‐type Complex Oxides K3MTa7O21 (M = Ti,Zr)

Potassium‐containing zirconium(IV)/titanium(IV) tantalum(V) oxides, K₃TiTa₇O₂₁ ( 1 ) and K₃ZrTa₇O₂₁ ( 2 ), of K₃Nb₈O₂₁‐type of compounds are afforded from potassium‐molybdate flux. Both compounds crystallize in the hexagonal space group P6₃/mcm (no. 193) with a = 908.69(2), c = 1202.83(7) pm and c/a = 1.324 (Z = 2) for 1 and a = 913.30(3), c = 1219.21(6) pm and c/a = 1.335 (Z = 2) for 2 , respectively. The Structural motif of [MTa₇O₂₁]^3– (M = Ti⁴⁺ or Zr⁴⁺) consists of edge‐shared (M,Ta)₆O₂₄‐units that are similar to corner‐sharing Ta₆O₂₇ units of synthetic soro‐silicate K₃Ta₃Si₂O₁₃ and double borate K₃Ta₃B₂O₁₂. The solid state bandgap measurements revealed that calculated values (3.26 eV for K₃TiTa₇O₂₁ and 3.14 eV for K₃ZrTa₇O₂₁) are dependent on aperture of Ta–O–Ta bond angle as it was previously shown for perovskite‐type tantalate photocatalysts.     

Die metallreiche Schichtstruktur von Ta6STe3

The Metal‐rich Layer Structure of Ta₆STe₃ Ta₆S_1+xTe_3–x was prepared from an appropriate mixture of 2 H–Ta_1.3S₂, TaTe₂, and Ta in a fused tantalum tube at 1273 K within 3 d. The results of a X‐ray single crystal structure analysis for a phase near the Te‐rich limit of the homogeneity range are reported. Ta₆S_1.00Te_3.00(1) crystallizes in the triclinic space group P1, a = 993.14(8) pm, b = 1032.18(8) pm, c = 1378.78(11) pm, α = 79.32(1)°, β = 81.36(1)°, γ = 85.74(1)°, Z = 6, Pearson symbol aP60, 6048 I_o > 2σ (I_o), 286 variables, wR₂ = 0.067. The metal‐rich layer structure of Ta₆STe₃ comprises distorted icosahedral Ta₁₃ clusters and related deltahedral cluster fragments complemented by chalcogen atoms. The centred clusters consist of 11, 12, 13, 14, or 16 atoms. They interpenetrate into lamellae in which the tantalum and chalcogen atoms are spatially segregated according to [Q–Ta₃–Q]. The signature of the structure is a lenticular heptagonal antiprismatic Ta₃₀ cluster which seems to be excised from the pentagonal antiprismatic columnar structure of Ta₆S. The Ta₃₀ clusters and distorted icosahedral Ta₁₃ clusters are connected and fused into puckered layers. The rest of the tantalum valences are used for heteronuclear bonding. The chalcogen atoms having three to six next tantalum atoms coat the corrugated, tetrahedrally close‐packed layers. Ta₆STe₃ is a moderate metallic conductor (ρ_{293 K} = 3 × 10^–4 Ωcm) exhibiting typical temperature independent paramagnetic properties.     

Pyrochlore and Perovskite Potassium Tantalate: Enthalpies of Formation and Phase Transformation

Alkali niobates and tantalates are currently important lead‐free functional oxides. The formation and decomposition energetics of potassium tantalum oxide compounds (K₂O?Ta₂O₅) were measured by high‐temperature oxide melt solution calorimetry. The enthalpies of formation from oxides of KTaO₃ perovskite and defect pyrochlores with K/Ta ratio of less than 1 stoichiometry—K_0.873Ta_2.226O₆, K_1.128Ta_2.175O₆, and K_1.291Ta_2.142O₆—were experimentally determined, and the values are (?203.63±2.92) kJ mol^?1 for KTaO₃ perovskite, and (?339.54±5.03) kJ mol^?1, (?369.71±4.84) kJ mol^?1, and (?364.78±4.24) kJ mol^?1, respectively, for non‐stoichiometric pyrochlores. That of stoichiometric defect K₂Ta₂O₆ pyrochlore, by extrapolation, is (?409.87±6.89) kJ mol^?1. Thus, the enthalpy of the stoichiometric pyrochlore and perovskite at K/Ta=1 stoichiometry are equal in energy within experimental error. By providing data on the thermodynamic stability of each phase, this work supplies knowledge on the phase‐formation process and phase stability within the K₂O?Ta₂O₅ system, thus assisting in the synthesis of materials with reproducible properties based on controlled processing. Additionally, the relation of stoichiometric and non‐stoichiometric pyrochlore with perovskite structure in potassium tantalum oxide system is discussed.     

Europium(II) oxy­iodide

Yellow single crystals of Eu₄OI₆ were grown from fluxes in Ta ampoules and structurally characterized by X‐ray diffraction. Eu₄OI₆ crystallizes in a hexagonal system and is isotypic with the corresponding chloride and bromide compounds. The O atom and one Eu atom lie on sites with 3m symmetry; the other Eu atom and the two unique I atoms are at sites with m symmetry. The structure is characterized by O‐centered tetrahedra of divalent europium cations [Eu—O = 2.391 (15) and 2.416 (5) Å, and mean Eu—Eu = 3.94 Å] and hexagonal channels along [001] filled with iodide anions.     

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 Si^2–]^6–. Magnetic susceptibility investigations of Eu₅Si₃ show Curie-Weiss behaviour above 100 K with a magnetic moment of 7.85(5) μ_B which is close to the free ion value of 7.94 μ_B for Eu²⁺. Chemical bonding in Eu₅Si₃ and Yb₃Si₅ was investigated by semi-empirical band structure calculations using an extended Hückel 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 Oxochlorotantalate (PPh4)2[Ta2OCl9]2 · 2 CH2Cl2, (PPh4)2[Ta2OCl10] · 2 CH3CN und (K-18-Krone-6)4[Ta4O6Cl12] · 12 CH2Cl2

The Oxochlorotantalates (PPh₄)₂[Ta₂OCl₉]₂ · 2 CH₂Cl₂, (PPh₄)₂[Ta₂OCl₁₀] · 2 CH₃CN, and (K-18-crown-6)₄[Ta₄O₆Cl₁₂] · 12 CH₂Cl₂ (K-18-crown-6)₄[Ta₄O₆Cl₁₂] · 12 CH₂Cl₂ was obtained from a reaction of tantalum pentachloride, K₂S₅ and 18-crwon-6 in dichlormethane. According to its crystal structure analysis it is tetragonal (space group I 4 2d) and contains [Ta₄O₆Cl₁₂]^4– ions that have an adamantane-like Ta₄O₆ skeleton. Each K⁺ ion is coordinated by the oxygen atoms of the crown ether molecule from one side and with three Cl atoms of one [Ta₄O₆Cl₁₂]^4– ion from the opposite side. (PPh₄)₂[Ta₂OCl₁₀] · 2 CH₃CN was a product from PPh₄Cl and TaCl₅ in acetonitrile in the presence of Na₂S₄. Its crystals are monoclinic (space group P2₁/c) and contain centrosymmetric [Ta₂OCl₁₀]^2– ions having a linear Ta–O–Ta grouping with short bonds (Ta–O 189 pm). TaCl₅ and H₂S formed a solid substance (TaSCl₃) from which a small amount of (PPh₄)₂[Ta₂OCl₉]₂ · 2 CH₂Cl₂ was obtained by the reaction with PPh₄Cl in CH₂Cl₂. The anions in the monoclinic crystals (space group P2₁/n) consist of two Ta₂OCl₉^– units which are joined by chloro bridges; each Ta₂OCl₉^– unit has a nearly linear Ta–O–Ta group with differing bond lengths (179 and 202 pm). The oxygen in the compounds probably was introduced by traces of water in the crown ether, acetonitrile or H₂S, respectively.     

Peroxofluorokomplexe der Übergangsmetalle. III,Darstellung, Kristallstruktur und Schwingungsspektren von K6Ta3(O2)3OF13 · H2O mit einem μ-Oxo-diperoxo-octafluoroditantalat(V)-Anion

Transition Metal Peroxofluoro Complexes. III. Preparation, Crystal Structure, and Vibrational Spectra of K₆Ta₃(O₂)₃OF₁₃ · H₂O Containing a m?-Oxo-diperoxo-octafluoroditantalate(V) Anion K₆Ta₃(O₂)₃OF₁₃ · H₂O has been prepared from solution and his crystal structure was determined by X-ray single crystal investigation: Space group Pnma, lattice constants a = 1 653.6 pm, b = 883.5 pm, c = 1 365.8 pm, Z = 4, R = 0.033. The compound yields [Ta(O₂)F₅]^2? groups as well as m?-oxo-bridged [Ta₂O(O₂)₂F₈]^4? anions with very diffrent O? O distances within the peroxo groups (139 pm vs. 164 and 175 pm) correlating well with the i.r. and Raman spectra. The different bonding in connection with an oxo-bridge is discussed.     

Eu5F[SiO4]3 und Yb5S[SiO4]3: Gemischtvalente Lanthanoid‐Silicate mit Apatit‐Struktur

Eu₅F[SiO₄]₃ and Yb₅S[SiO₄]₃: Mixed‐Valent Lanthanoid Silicates with Apatite‐Type of Structure By the reaction of Eu, EuF₃, Eu₂O₃ with SiO₂ in evacuated gold ampoules, using NaF as flux, at a temperature of 1000 °C for ten hours, dark‐red, platelet‐shaped single crystals of Eu₅F[SiO₄]₃ are obtained. Similarly dark‐red, but pillar‐shaped single crystals of Yb₅S[SiO₄]₃ are obtained by the reaction of Yb, Yb₂O₃ and S with SiO₂ in the presence CsBr as flux in evacuated silica ampoules at 850 °C and an annealing time of seven days. Both compounds crystallize hexagonally (P6₃/m, Z = 2; Eu₅F[SiO₄]₃: a = 954.79(9), c = 704.16(6) pm; Yb₅S[SiO₄]₃: a = 972.36(9), c = 648.49(6) pm) in the case of Eu₅F[SiO₄]₃ analogous to the mineral fluorapatite and for Yb₅S[SiO₄]₃ as a bromapatite—type variety. The crystal structure containing isolated [SiO₄]^4— tetrahedra distinguishes two rare‐earth cation positions with coordination numbers of nine (M1) and seven (M2), in which the position M1 of the europium fluoride silicate is almost exclusively occupied by Eu²⁺ cations, whereas in ytterbium sulfide silicate it contains di‐ and trivalent Yb cations in the ratio 1 : 1. In both cases, however, the M2 position is only populated with M³⁺.     

Die Reaktionen von Europium und Yttrium mit N‐Iod‐triphenylphosphanimin. Kristallstrukturen von [EuI2(DME)3], [Eu2I(NPPh3)5(DME)] und [Y2I(NPPh3)4(THF)4]+I3–

The Reactions of Europium and Yttrium with N‐Iodinetriphenylphosphoraneimine. Crystal Structures of [EuI₂(DME)₃], [Eu₂I(NPPh₃)₅(DME)] and [Y₂I(NPPh₃)₄(THF)₄]⁺I₃^– When treated with ultrasound, the reaction of europium metal with INPPh₃ in 1,2‐dimethoxyethane (DME) leads to the complexes [EuI₂(DME)₃] ( 1 ) and [Eu₂I(NPPh₃)₅(DME)] ( 2 ) which are separated from each other by fractional crystallization. On the other hand, the reaction of yttrium metal with INPPh₃ under similar conditions in THF gives the ionic phosphoraneiminato complex [Y₂I(NPPh₃)₄(THF)₄]⁺I₃^– ( 3 ). All complexes are characterized by crystal structure determinations. 1 : Space group P2₁, Z = 2, lattice dimensions at 188 K: a = 848.9(1); b = 1059.4(1); c = 1227.9(1) pm; β = 93.793(6)°; R = 0.0246. In the molecular structure of 1 the europium atom is eightfold coordinated with a bond angle I–Eu–I of 158.51°. 2 · 2 DME: Space group P1, Z = 2, lattice dimensions at 193 K: a = 1405.5(1); b = 1652.2(2); c = 2203.7(2) pm; α = 89.404(11)°; β = 72.958(11)°; γ = 78.657(11)°; R = 0.0391. In 2 the europium atoms are linked by the μ‐N‐atoms of two (NPPh₃^–) groups to form a planar Eu₂N₂ four‐membered ring. One of the Eu atoms is terminally coordinated by the N atoms of two (NPPh₃^–) groups, thus achieving a distorted tetrahedral surrounding. The second Eu atom is coordinated by the N atom of one (NPPh₃^–) group, by the terminally bounded iodine atom and by the oxygen atoms of the DME chelate, thus achieving a distorted octahedral surrounding. 3 · 6¹/₂ THF: Space group P1, Z = 2, lattice dimensions at 103 K: a = 1739.7(2); b = 1770.1(2); c = 2153.8(3) pm; α = 74.929(15)°; β = 84.223(14)°; γ = 64.612(12)°; R = 0.0638. In the cation [Y₂I(NPPh₃)₄(THF)₄]⁺ of 3 the yttrium atoms are linked by the μ‐N atoms of two (NPPh₃^–) groups as well as by the μ‐I atom. One (NPPh₃^–) ligand and two THF molecules complete the distorted octahedral coordination at each yttrium atom.     

Rubidium‐ und Caesium‐Verbindungen mit dem Isopolyanion [Ta6O19]8– – Synthesen,Kristallstrukturen, thermische und schwingungsspektroskopische Untersuchungen der Oxotantalate A8[Ta6O19] · n H2O (A = Rb,Cs; n = 0, 4, 14)

Rubidium und Caesium Compounds with the Isopolyanion [Ta₆O₁₉]^8– – Synthesis, Crystal Structures, Thermogravimetric and Vibrational Spectrocopic Analysis of the Oxotantalates A₈[Ta₆O₁₉] · n H₂O (A = Rb, Cs; n = 0, 4, 14) The compounds A₈[Ta₆O₁₉] · n H₂O (A = Rb, Cs; n = 0, 4, 14) contain the isopoly anion [Ta₆O₁₉]^8–, which consists of six [TaO₆] octahedra connected via corners to form a large octahedron. They transform into each other by reversible hydratation/dehydratation processes, as shown from thermoanalytic measurements (TG/DSC), and show also structural similarities. Cs₈[Ta₆O₁₉] (tetragonal, I4/m, a = 985.9(1) pm, c = 1403.3(1) pm, Z = 2), the isotypic phases A₈[Ta₆O₁₉] · 14 H₂O (A = Rb/Cs; monoclinic, P2₁/n, a = 1031.30(6)/1055.4(1) pm, b = 1590.72(9)/1614.9(6) pm, c = 1150.43(6)/1171.4(1) pm, β = 100.060(1)/99.97(2)°, Z = 2) and Rb₈[Ta₆O₁₉] · 4 H₂O (monoclinic, C2/c, a = 1216.9(4) pm, b = 1459.2(5) pm, c = 1414.7(4) pm, β = 90.734(6)°, Z = 4) have been characterised on the basis of single crystal x‐ray data. Furthermore the RAMAN spectra allow a detailled comparison of the hexatantalate ions in the four compounds.     

Ca1.5Eu3Sn0.5O7: a calcium europium tin oxide with a novel structure

A new quaternary compound in the Ca–Eu–Sn–O system, namely calcium europium tin hepta­oxide, Ca_1.5Eu₃Sn_0.5O₇, was prepared by solid‐state reaction at 2073 K. All atoms in the structure are on 4i special positions (on mirrors) in space group C2/m. Ca/Eu sites are situated within two O octa­hedra and within two sevenfold coordination sites surrounded by O‐capped trigonal prisms. A Ca/Eu/Sn site is coordinated by five O atoms. The structural formula can be represented as (Ca_0.28Eu_0.72)(Ca_0.16Eu_0.84)(Ca_0.46Eu_0.54)(Ca_0.28Eu_0.72)(Ca_0.32Eu_0.18Sn_0.50)O₇. The crystal structure is a new type and is related to the structure of B‐form Eu₂O₃.     

Inverse Perovskites (Eu3O)E with E = Sn,In – Preparation,Crystal Structures and Physical Properties

The cubic inverse Perovskites (Eu₃O)In and (Eu₃O)Sn were prepared from the metals and Eu₂O₃ or SnO₂, respectively. For (Eu₃O)In the crystal structure analysis was performed on single crystal X‐ray diffraction data (space group , a = 512.79(3) pm, Z = 1, R_gt(F) = 0.022, wR(F²) = 0.044). The data indicated full occupancy on all sites and a fully ordered structure. According to magnetic susceptibility measurements and X‐ray absorption spectroscopic data at the Eu L_III edge both compounds contain europium in the 4f⁷ (Eu²⁺) electronic state. (Eu₃O)In orders ferromagnetically at 185(5) K, (Eu₃O)Sn shows antiferromagnetic order at 31.4(2) K. Both compounds behave as metallic conductors in electrical resistivity measurements. However, (Eu₃O)In may be classified a metal, while (Eu₃O)Sn is more likely a heavily doped degenerated semiconductor or semimetal according to the absolute values of the resistivity.     

Sr13□NbAs11 and Eu13□NbAs11 – Defect Variants of the Ca14AlSb11 Structure with asymmetric [As3]7− anions

The novel compounds Sr₁₃NbAs₁₁ and Eu₁₃NbAs₁₁ have been synthesized from SrAs, Eu₅As₄, Sr, Nb and As in niobium ampoules at 1173–1273 K. The tetragonal tI 200 phases are defect variants of the Ca₁₄AlSb₁₁ structure (space group I4₁/acd (no. 142); Sr₁₃□NbAs₁₁: a = 1649.8(2) and c = 2214.1(3); Eu₁₃□NbAs₁₁: a = 1632.9(8) and c = 2197.3(8) pm; Z = 8). The structures are built from the cations Sr²⁺, and Eu²⁺, respectively, and from the anions [NbAs₄]^7?, As^3?, and the linear polyanion [As₃]^7?. This polyanion (isosteric to I₃^?) is asymmetric with d(As? As) = 273.0 and 346.0 pm (Sr) and 274.7 and 335.6 pm (Eu), respectively. The bond lengths in the tetrahedral anions are d(Nb? As) = 250.8 and 251.1 pm. The complete structural arrangement is related to that of Cu₂O by forming two interpenetrating networks. The oxygen atoms are substituted by niobium centered As₄ tetrahedra, and the Cu atoms are substituted by As₆ octahedra (centered by Sr, Eu). The central As atoms of the polyanions connect the nets. Both As networks are enveloped by the remaining cations forming cubes, tetragonal antiprisms and capped trigonal prisms.     

Eu(ClO4)3: First Single Crystals of an Anhydrous Rare‐Earth Perchlorate

Single crystals of Eu(ClO₄)₃ have been obtained by slow dehydration of a hydrous product prepared by the reaction of Eu₂O₃ with HClO₄. The crystal structure (hexagonal, P6₃/m, Z = 2, a = 924.96(9), c = 574.86(8) pm) consists of tricapped trigonal [EuO₉] prisms and [ClO₄] tetrahedra. One of the oxygen atoms in the ClO₄ group does not coordinate to Eu³⁺ and points towards the empty channel which runs in the direction [001].     

Structure and Properties of EuZnGa

New ternary gallide EuZnGa was synthesized by reaction of the elements in a sealed tantalum tube at 1320 K and subsequent annealing at 970 K for seven days. EuZnGa was investigated by X‐ray diffraction on both powders and single crystals. Its structure was refined from single crystal diffractometer data: KHg₂ type, space group Imma, a = 461.7(2), b = 761.4(3), c = 777.0(3) pm, R = 0.041 for 486 structure factors and 13 variables. The zinc and gallium atoms statistically occupy the mercury position of the KHg₂ type of structure. No long‐range ordering between the zinc and gallium atoms could be detected from the X‐ray data. Magnetic susceptibility measurements show Curie‐Weiss behavior above 50 K with a magnetic moment of μ_exp = 7.86(5) μ_B/Eu and θ = 17(2) K, suggesting divalent europium. Low‐field, low‐temperature susceptibility measurements indicate cluster glass behavior (mictomagnetism) with a freezing temperature of 24(2) K. Magnetization measurements show a magnetic moment of 4.9(1) μ_B/Eu at 2 K and a magnetic flux density of 5.5 T. Electrical resistivity data indicate metallic behavior. ¹⁵¹Eu Mössbauer spectroscopic measurements show onset of magnetic hyperfine splitting at ≤ 17.0 K. Down to the temperature of 4.2 K the spectra reflect magnetic relaxation effects suggesting the presence of a substantial extent of disordering. This observation is consistent with the cluster glass behavior as evident from the magnetic susceptibility data and may be a consequence of the presence of multiple local Eu sites as expected from the statistical Zn and Ga distribution over the corresponding sites in the KHg₂ structure.     

X-ray and neutron powder diffraction study of the order-disorder transition in Eu2IrH5 and the mixed crystal compounds Eu2−xAxIrH5 (A=Ca, Sr; x=1.0, 1.5)

The title compounds and their deuterides have been prepared by solid-state and solid-gas reactions from the elements and investigated by X-ray and neutron powder diffraction as a function of temperature. At room temperature they crystallize with an anion-deficient cubic K₂PtCl₆-type structure (space group ) in which five hydrogen (deuterium) atoms surround iridium randomly on six octahedral sites with average bond distances of Ir-D=169-171 pm. At low temperature they undergo a tetragonal deformation (space group I4/mmm) to the partially ordered Sr₂IrD₅ (T=4.2K)-type structure in which four hydrogen (deuterium) atoms occupy planar sites with full occupancy (Ir-D=166-170 pm) and two hydrogen (deuterium) atoms axial sites (Ir-D=174-181 pm) with ∼50% occupancy, i.e., the data are consistent with a mixture of square-pyramidal [IrD₅]⁴⁻ complexes pointing in two opposite directions. The transitions occur at ∼240 K (Eu_0.5Ca_1.5IrD₅, Eu_0.5Sr_1.5IrD₅), ∼210 K (EuSrIrD₅), ∼200 K (EuCaIrD₅, Eu₂IrD₅), and are presumably of first order.