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.     

Structural Distortion in Perovskite Type KCaH3–xFx (0.54 ≤ x ≤ 3)

Representatives of the solid solution series KCaH_3–xF_x were synthesized by solid state reactions from binary metal hydrides and fluorides. Crystal structures were analyzed by Rietveld refinement based on X-ray powder diffraction. The degree of substitution was determined by refinement of site occupancy factors as well as elemental analysis for hydrogen. Three sections of x in KCaH_3–xF_x can be distinguished. For x < 0.54 no hydride fluoride exists, i.e. there is no hydride of the composition KCaH₃ and the solid solution starts only at x = 0.54. The tetragonal SrTiO₃ type structure with partial ordering of hydrogen and fluorine atoms is found for 0.54 ≤ x ≤ 1.7. Both anion positions show mixed occupation with some preference of hydrogen atoms for 8h and fluorine atoms for 4a sites (I4/mcm, SrTiO₃ type). For fluorine-rich compounds a solid solution with orthorhombic GdFeO₃ type structure (Pnma) and a perfectly statistical distribution of hydrogen and fluorine atoms is found (1.8 ≤ x ≤ 3). Interatomic distances resulting from the structure refinements are in the range of typical K–H, K–F, Ca–H, and Ca–F distances for mainly ionic compounds.     

The Hydrogenation of the Zintl Phase NdGa Studied by in situ Neutron Diffraction

The hydrogenation of the Zintl phase NdGa was studied by in situ neutron powder diffraction. We find a compositional range of 0.1 < x < 0.8 in NdGaH_1+x. Hydrogen atoms are located in two different positions, in HNd₄ tetrahedra, and close to the polyanionic chains. For the latter, the Ga–H distance in NdGaH_1.66 is quite long (ca. 200 pm) with a trigonal bipyramidal Nd₃Ga₂ surrounding of hydrogen atoms. Hydrogen poor NdGaH_<1 phases as known for similar systems were not observed. The changing hydrogen content shows no measureable effect on the unit cell volume, but on lattice parameter ratios. Superstructures occur for 0.53 < x < 0.66 and 0.73 < x < 0.8, leading to a doubling or tripling of the lattice parameter a. They are probably caused by partial hydrogen ordering. The threefold superstructure contains a ¹_∞[(Ga–H–Ga–H–Ga)^6–] moiety with hydrogen bridging two gallium chains.     

Eine neue Modifikation von Lanthanmonosilicid – lT-LaSi

A New Modification of Lanthanum Monosilicide – lT-LaSi La metal and silicon react at 950 °C in the presence of LaBr₃ to form LaSi with the hitherto unknown low temperature modification (lT-LaSi). lT-LaSi crystallizes in Cmcm with a = 456.21(2), b = 1348.03(5), c = 662.59(6) pm. The Si atoms are connected to form cis-trans-cis-trans chains with alternating distances of d_Si–Si = 248 and 260 pm. They are coordinated in a trigonal prismatic fashion by the La atoms. lT-LaSi shows metallic conductivity.     

The Crystal Structure of YPdSi,the Isotypic Compounds LnPdSi (Ln = Gd–Lu), and their Structural Relation to some other Equiatomic Compounds of the Rare Earth and Transition Metals with Main Group Elements

The nine title compounds were prepared from the elements by arc-melting and subsequent heat treatment in resistance and high-frequency furnaces. The crystal structure of these isotypic compounds was determined for YPdSi from single-crystal X-ray diffractometer data: Pmmn, a = 430.8(1) pm, b = 1391.2(1) pm, c = 743.1(1) pm, Z = 8, R = 0.024 for 417 structure factors and 40 variable parameters. The crystal structures of the isotypic compounds GdPdSi and ErPdSi were also refined from single-crystal data. The structure is of a new type. It consists of condensed, six-membered rings of alternating palladium and silicon atoms with Pd–Si bond distances varying between 249.6 and 258.8 pm. These two-dimensionally infinite nets are connected to each other via weak Pd–Si and Si–Si bonds with bond distances of 276.3 and 259.5 pm. The rare earth atoms are situated above and below the six-membered palladium-silicon rings in a manner as it is known for the aluminum atoms in the AlB₂ type structure. The crystal-chemical similarities and topologies of several structures derived from the aristotype AlB₂ (including those of BaPtSb, EuAuGe, KHg₂, ZrBeSi, and TiNiSi) are described, emphasizing their group-subgroup relationships. The previously reported compound ”︁Er₂Pd₂Si”︁”︁ has the same structure as has been found here for ErPdSi.     

Synthesis and Crystal Structures of Novel Copper(I) Clusters with Bridging Silyl Amide Ligands

Treatment of copper(I) chloride with R₂Si(NLiPh)₂ (R = Me, Ph) in thf led to the formation of the octanuclear cluster compounds [Cu₈{(R₂Si(NPh)₂}₄] [R = Me ( 1 ), Ph ( 2 ).] Compound 1 crystallizes in the tetragonal space group P4/n, with a = 1505.41(5) and c = 1911.32(7) pm. The X‐ray crystal structure determination revealed a cube shaped Cu₈ cluster core with μ₄ bridging Me₂Si(NPh)₂^2– ligands. The copper atoms display an almost linear coordination with Cu–N distances in the range of 191.1(3)–191.4(3) pm. The Cu–Cu distances are 265.7(1)–267.3(1) pm. Compound 2 forms monoclinic crystals, space group P2₁/n, with a = 1461.87(4), b = 2483.77(6), c = 2725.49(8) pm, β = 100.77(1)°. The cluster core of compound 2 consists formally of two mutually perpendicular arranged trigonal prisms, which share a common square face. Like in the case of compound 1 the square faces of the cluster core are capped by μ₄ bridging Ph₂Si(NPh)₂^2– ligands. The copper atoms adopt a nearly linear N–Cu–N coordination with Cu–N distances of 190.0(4)–195.1(4) pm. The Cu–Cu distances are 252.3(1)–305.6(1) pm.     

Hydrogenolysis of Polysilanes Catalyzed by Low-Valent Nickel Complexes

The dehydrogenation of organosilanes (R_xSiH_4−x) under the formation of Si−Si bonds is an intensively investigated process leading to oligo- or polysilanes. The reverse reaction is little studied. To date, the hydrogenolysis of Si−Si bonds requires very harsh conditions and is very unselective, leading to multiple side products. Herein, we describe a new catalytic hydrogenation of oligo- and polysilanes that is highly selective and proceeds under mild conditions. New low-valent nickel hydride complexes are used as catalysts and secondary silanes, RR′SiH₂, are obtained as products in high purity.     

Platinum‐Indium Polyanions in the Structures of LaPtIn4 and LnPtIn3 (Ln = La,Ce, Pr,Nd, Sm) and Structure Refinement of Ce2Pt2In

The title compounds were prepared by reacting the elements in an arc‐melting furnace and subsequent annealing. The LaRuSn₃ type structure of the new compounds LnPtIn₃ (Ln = La, Ce, Pr, Nd, Sm) was refined from single crystal X‐ray data for LaPtIn₃: Pm3n, a = 980.4(2) pm, wR2 = 0.0271, 399 F² values, 15 variables. Striking structural motifs of LaPtIn₃ are condensed distorted trigonal [PtIn₆] prisms with Pt–In distances of 269 pm. The lanthanum atoms occupy large cavities within the polyhedral network. Besides Pt–In bonding In–In bonding also plays an important role in LaPtIn₃ with In–In distances of 299 and 327 pm. The La1 position is occupied only to 91%, resulting in a composition La_0.98(1)PtIn₃. The La1 atoms show an extremely large displacement parameter indicating a rattling of these atoms in the In₁₂ cages. The so far most indium rich compound in the ternary system lanthanum‐platinum‐indium is LaPtIn₄ which was characterized on the basis of Guinier powder data: YNiAl₄‐type, Cmcm, a = 455.1(2) pm, b = 1687.5(5) pm, and c = 738.3(2) pm. The platinum atoms in LaPtIn₄ center trigonal prisms with the composition [La₂In₄]. Together with the indium atoms the platinum atoms form a complex three‐dimensional [PtIn₄] polyanion in which the lanthanum atoms occupy large hexagonal tubes. The structure of Ce₂Pt₂In is confirmed: Mo₂FeB₂‐type, P4/mbm, a = 779.8(1) pm, c = 388.5(1) pm, wR2 = 0.0466, 433 F² values, 12 parameters. It is built up from CsCl and AlB₂ related slabs with the compositions CeIn and CePt₂, respectively. Chemical bonding in the [PtIn₃] and [PtIn₄] polyanions of LaPtIn₃ and LaPtIn₄ is discussed.     

Structural and Electronic Flexibility in Hydrides of Zintl Phases with Tetrel–Hydrogen and Tetrel–Tetrel Bonds

The hydrogenation of Zintl phases enables the formation of new structural entities with main‐group‐element–hydrogen bonds in the solid state. The hydrogenation of SrSi, BaSi, and BaGe yields the hydrides SrSiH_{5/3−x ,} BaSiH_5/3−x and BaGeH_5/3−x . The crystal structures show a sixfold superstructure compared to the parent Zintl phase and were solved by a combination of X‐ray, neutron, and electron diffraction and the aid of DFT calculations. Layers of connected HSr₄ (HBa₄) tetrahedra containing hydride ions alternate with layers of infinite single‐ and double‐chain polyanions, in which hydrogen atoms are covalently bound to silicon and germanium. The idealized formulae AeTt H_5/3 (Ae =alkaline earth, Tt =tetrel) can be rationalized with the Zintl–Klemm concept according to (Ae ²⁺)₃(Tt H⁻)(Tt ₂H²⁻)(H⁻)₃, where all Tt atoms are three‐binding. The non‐stoichiometry (SrSiH_5/3−x , x =0.17(2); BaGeH_5/3−x , x =0.10(3)) can be explained by additional π‐bonding of the Tt chains.     

Die Undecaarsenide A3As11 (A = Rb,Cs) — Synthesen und Kristallstrukturen

Alkaline Metal Arsenides A₃As₁₁ (A = Rb, Cs): Preparation and Crystal Structures Rb₃As₁₁ and Cs₃As₁₁ were synthesized from the elements and the crystal structures of the ordered room temperature form were characterized via single crystal x‐ray studies. In the Zintl phases the As atoms form chiral ufosan‐anions As with As‐As distances ranging from 238 to 248 pm. Like K₃As₁₁ Rb₃As₁₁ crystallizes with the Na₃P₁₁ structure type (orthorhombic, space group Pbcn, a = 1108.2(2), b = 1533.5(3), c = 1060.1(2) pm, Z = 4), whereas the Cs compound (monoclinic, space group C2/c, a = 1324.5(7), b = 1524.5(9), c = 1937.2(11) pm, β = 95.29(1)°, Z = 8) forms a new structure type. The crystallographic relationship between the two structure types and the anion packings in the plastic crystalline high temperature forms are discussed.     

In situ Investigations on the Formation and Decomposition of KSiH3 and CsSiH3

The system KSi‐KSiH₃ stores 4.3 wt % of hydrogen and shows a very good reversibility at mild conditions of 0.1 MPa hydrogen pressure and 414 K. 1 We followed the reaction pathways of the hydrogenation reactions of KSi and its higher homologue CsSi by in situ methods in order to check for possible intermediate hydrides. In situ diffraction at temperatures up to 500 K and gas pressures up to 5.0 MPa hydrogen gas for X‐ray and deuterium gas for neutron reveal that both KSi and CsSi react in one step to the hydrides KSiH₃ and CsSiH₃ and the respective deuterides. Neither do the Zintl phases dissolve hydrogen (deuterium), nor do the hydrides (deuterides) show any signs for non‐stoichiometry, i.e. all phases involved in the formation are line phases. Heating to temperatures above 500 K shows that at 5.0 MPa hydrogen pressure only the reaction 2CsSi + 3H₂ = 2CsSiH₃ is reversible. Under these conditions, KSiH₃ decomposes to a clathrate and potassium hydride according to 46KSiH₃ = K₈Si₄₆ + 38KH + 50H₂.     

Nd3Si5AlON10 – Synthese,Kristallstruktur und Eigenschaften eines Sialons im La3Si6N11‐Strukturtyp

Nd₃Si₅AlON₁₀ – Synthesis, Crystal Structure, and Properties of a Sialon Isotypic with La₃Si₆N₁₁ Nd₃Si₅AlON₁₀ was synthesized by the reaction of silicon diimide, aluminium nitride, aluminium oxide, and neodymium in a pure nitrogen atmosphere at 1650 °C using a radiofrequency furnace. The compound was obtained as a coarsely crystalline solid. According to the single‐crystal structure determination the title compound is isotypic with Ln₃Si₆N₁₁ (Ln = La, Ce, Pr, Nd, Sm). Nd₃Si₅AlON₁₀ (P4bm, a = 1007.8(1), c = 486.3(1) pm, Z = 2, R₁ = 0.016, wR₂ = 0.031) is built up by a three‐dimensional network structure of corner sharing SiON₃ and (Si/Al)N₄ tetrahedra (molar ratio Si : Al = 3 : 1). According to lattice energetic calculations using the MAPLE concept a differentiation of O and N seems to be reasonable. One of the two different sites for the tetrahedral centres is probably occupied by Si (distances: Si–O: 168.4(1), Si–N: 173.6(3)–176.0(4) pm) the second site by Si and Al with the molar ratio 3 : 1 (distances: (Si/Al)–N: 172.0(3)–176.6(2) pm). The Nd³⁺ ions are located in the voids of the (Si₅AlON₁₀)^9– framework (distances: Nd–O: 261.07(8), Nd–N: 246.1(2)–286.6(2) pm).     

Crystal Structure and Formation of TlPd3 and its new Hydride TlPd3H

TlPd₃ was synthesised from the elements in evacuated silica tubes at 600 °C. Alternatively, TlPd₃ was yielded by reduction of TlPd₃O₄ in N₂ gas atmosphere. Reduction of the oxide in H₂ gas atmosphere resulted in the formation of the new hydride TlPd₃H. The structure of tetragonal TlPd₃ (ZrAl₃ type, space group I4/mmm, a = 410.659(9) pm, c = 1530.28(4) pm) was reinvestigated by X‐ray and also by neutron powder diffraction as well as the structure of its previously unknown hydride TlPd₃H (cubic anti‐perovskite type structure, space group Pm\bar{3} m, a = 406.313(1) pm). In situ DSC measurements of TlPd₃ in hydrogen gas atmosphere showed a broad exothermic signal over a wide temperature range with two maxima at 280 °C and at 370 °C, which resulted in the product TlPd₃H. A dependency of lattice parameters of the intermetallic phase on reaction conditions is observed and discussed. Results of hydrogenation experiments at room temperature with gas pressures up to 280 bar hydrogen and at elevated temperatures with very low hydrogen gas pressures (1–2 bar) as well as results of dehydrogenation of the hydrides under vacuum will be discussed.     

MHSe: The First Hydride Selenides of the Lanthanides (M = La?Nd; Gd?Er,Lu)

The oxidation of most of the lanthanide dihydrides MH₂ (M = La? Nd; Gd? Er, Lu) with equimolar amounts of selenium results in the formation of the first lanthanide hydride selenides MHSe. The presence of alkali chlorides (e.g., NaCl or CsCl) as fluxes secures complete and fast reactions (7 d) at 700–850°C in sealed, arc-welded tantalum capsules (protected by evacuated silica vessels) as well as single-crystalline products (pale bluish-gray hexagonal columns or platelets). Two different structures were determined from X-ray single crystal data for the examples of 2H? CeHSe (hexagonal, P6₃/mmc (no. 194), Z = 2, a = 406.36(4), c = 794.81(9) pm, R1 = 0.0365, wR2 = 0.0766) and 1H? HoHSe (hexagonal, P6 m2 (no. 187), Z = 1, a = 381.56(3), c = 387.28(5) pm, R1 = 0.0140, wR2 = 0.0337). According to X-ray powder data, the hydride selenides MHSe with M = La? Nd proved to be isostructural with 2H-CeHSe, those with M = Gd? Er and Lu crystallize isotypically with 1H? HoHSe just like YHSe. Both structures contain hydrogen in half of the trigonal planar interstices within closest-packed mono-layers of the metals. These layers [(M³⁺)(H^?)_3/3]²⁺ (a,β or b,α) are alternatively sheethed with closest-packed mono-layers of Se^2? (C) along [001], and only the stacking sequence decides whether a “stuffed” WC- (C(a,β)C ? 1 H-MHSe) or a “stuffed” anti-NiAs-type arrangement (C(a,β)C(b,α)C ? 2H? MHSe) emerges.     

Lanthanoid Antimonides Ln2Sb5 (Ln = Sm,Gd, Tb,Dy) and Rationalization of Chemical Bonding within the Antimony Polyanion by Combining the Zintl‐Klemm Concept with Bond‐Length Bond‐Strength Relationships

The title compounds are formed by peritectic reactions. Single crystals could be isolated from samples with high antimony content. Their structure was determined for Dy₂Sb₅ from four‐circle X‐ray diffractometer data: P2₁/m, a = 1306.6(1) pm, b = 416.27(4) pm, c = 1458.4(1) pm, β = 102.213(8)°, Z = 4, R = 0.061 for 2980 structure factors and 86 variable parameters. All dysprosium atoms have nine antimony neighbors forming tricapped trigonal prisms with Dy–Sb distances varying between 308 and 338 pm. The antimony atoms occupy ten different sites with greatly varying coordination. One extreme case is an antimony atom surrounded only by dysprosium atoms in trigonal prismatic arrangement, the other one is an antimony atom in distorted octahedral antimony coordination. The various antimony‐antimony interactions (with Sb–Sb distances varying between 284 and 338 pm) are rationalized by combining the Zintl‐Klemm concept with bond‐length bond‐strength considerations.     

La-H化合物对LaMg2Ni合金中Mg2Ni相吸氢过程的影响

采用感应熔炼技术在Ar气氛保护下制备得到LaMg2Ni与Mg2Ni合金。X射线衍射(XRD)图表明LaMg2Ni合金在吸氢过程中分解为LaH3相和Mg2NiH4相,放氢过程中LaH3相转化为La3H7相。与Mg2Ni合金相比,LaMg2Ni合金显示出优良的吸氢动力学性能,这是由于镧氢化合物的存在及其在吸氢过程中所发生的相转变所造成的。LaMg2Ni合金280 s内吸氢即可达到最大储氢量的90%以上,而Mg2Ni合金则需要1200 s才能达到,且在相同温度下LaMg2Ni合金的吸氢反应速率常数大于Mg2Ni合金速率常数。镧氢化合物不仅有利于改善动力学性能,而且可以提高热力学性能。LaMg2Ni合金中的Mg2Ni相氢化反应焓与熵分别为-53.02 kJ.mol-1和84.96 J.K-1.mol-1(H2),这一数值小于单相Mg2Ni氢化反应焓与熵(-64.50 kJ.mol-1,-123.10 J.K-1.mol-1(H2))。压力-组成-温度(P-C-T)测试结果表明在603 K至523 K温度范围内,LaMg2Ni合金储氢容量保持稳定为1.95wt%左右,然而Mg2Ni合金的储氢容量则由4.09wt%衰减为3.13wt%,Mg2Ni合金的储氢容量在523K低温下仅为603 K时的76.5%,表明镧氢化合物能够改善Mg2Ni合金低温下的吸放氢性能。     

Synthese und Kristallstruktur von Cadmium‐Dodekahydro‐closo‐Dodekaborat‐Hexahydrat,Cd(H2O)6[B12H12]

Synthesis and Crystal Structure of Cadmium Dodecahydro closo‐Dodecaborate Hexahydrate, Cd(H₂O)₆[B₁₂H₁₂] Through neutralization of the aqueous free acid (H₃O)₂[B₁₂H₁₂] with cadmium carbonate (CdCO₃) and after isothermic evaporation of the resulting solution, colourless lath‐shaped single crystals of Cd(H₂O)₆[B₁₂H₁₂] are obtained. Cadmium dodecahydro closo‐dodecaborate hexahydrate crystallizes at room temperature in the monoclinic system (space group: C2/m) with the lattice constants a = 1413.42(9), b = 1439.57(9), c = 749.21(5) pm and β = 97.232(4)° (Z = 4). The crystal structure of Cd(H₂O)₆[B₁₂H₁₂] can be regarded as a monoclinic distortion variant of the CsCl‐type structure. Two crystallographically different [Cd(H₂O)₆]²⁺ octahedra (d(Cd–O) = 227–230 pm) are present which only differ in their relative orientation. The intramolecular bond lengths for the quasi‐icosahedral [B₁₂H₁₂]^2? cluster anions range in the intervals usually found for dodecahydro closo‐dodecaborates (d(B–B) = 177–179 pm, d(B–H) = 103–116 pm). The hydrogen atoms of the [B₁₂H₁₂]^2? clusters have no direct coordinative influence on the Cd²⁺ cations. Due to the fact that no “zeolitic” crystal water molecules are present, a stabilization of the lattice takes place mainly via the B–H^δ?···^+δH–O hydrogen bonds.     

Ternary Rhodium Borides A3Rh5B2 (A = Mg,Sc) and Quaternary Derivatives A2MRh5B2. Preparation,Crystal Structure (M = Main Group and 3 d Elements), and Magnetism (M = Mn,Fe)

The new ternary rhodium borides Mg₃Rh₅B₂ and Sc₃Rh₅B₂ (P4/mbm, Z = 2; a = 943.4(1) pm, c = 292.2(1) pm and a = 943.2(1) pm, c = 308.7(1) pm, respectively) crystallize with the Ti₃Co₅B₂ type structure. Mg and Sc may in part be substituted by a variety of elements M. For M = Si and Fe, homogeneity ranges were found according to A_3–xM_xRh₅B₂ with 0 ≤ x ≤ 1.0 for A = Sc and with x up to 1.5 for A = Mg. Quaternary compounds with x = 1 (A₂MRh₅B₂: A/M in short) were prepared with M = Be, Al, Si, P, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Sn (Co, Ni only with A = Mg; Sn only with A = Sc; P, As with deficiencies). Single crystal X‐ray investigations show an ordered substitutional variant of the Ti₃Co₅B₂ type in which the M atoms are arranged in chains along [001] with intrachain and interchain M–M distances of about 300 pm and 660 pm, respectively. Measuring the magnetisation (1.7 K–800 K) of the phases Mg/Mn, Sc/Mn, Mg/Fe, and Sc/Fe reveals antiferromagnetic interactions in the first and dominating ferromagnetic intrachain interactions in the remaining ones. Interchain interactions of antiferromagnetic nature are evident in Sc/Mn and Mg/Fe leading to metamagnetism below T_N = 130 K, while Sc/Fe behaves ferromagnetically below T_C = 450 K. The overall trend towards stronger ferromagnetic interactions with increasing valence electron concentration is obvious.     

Darstellung und Kristallstruktur der bekannten Zintl‐Phasen Cs3Sb7 und Cs4Sb2

Synthesis and Crystal Structure of the known Zintl Phases Cs₃Sb₇ and Cs₄Sb₂ Cs₃Sb₇ and Cs₄Sb₂ were synthesized from the elements and their crystal structures were determined on the basis of single crystal x‐ray data. Cs₃Sb₇ crystallizes in the monoclinic system with space group P2₁/c (a = 1605.7(1) pm, b = 1571.1(1) pm, c = 2793.9(2) pm, β = 96.300(2)°, Z = 16) and contains anions Sb₇^3–. In the structure of Cs₄Sb₂ (orthorhombic, space group Pnma, a = 1598.5(3) pm, b = 631.9(2) pm, c = 1099.5(2) pm, Z = 4) dumbbells Sb₂^4– are present.     

The Zintl Phase Eu2Si

The Zintl phase Eu₂Si was synthesized from elemental europium and silicon in a sealed tantalum tube in a high‐frequency furnace at 1270 K and subsequent annealing at 970 K. Investigation of the sample by X‐ray powder and single crystal techniques revealed: Co₂Si (anti‐PbCl₂) type, space group Pnma, a = 783.0(1), b = 504.71(9), c = 937.8(1) pm, wR2 = 0.1193, 459 F² values and 20 variables. The structure contains two europium and one silicon site. ¹⁵¹Eu Mössbauer spectroscopic data show a single signal at an isomer shift of −9.63(3) mm/s, compatible with divalent europium. Within the Zintl concept electron counting can be written as (2Eu²⁺)⁴⁺Si⁴⁻, in agreement with the absence of Si‐Si bonding. Each silicon atom has nine europium neighbors in the form of a tri‐capped trigonal prism. The silicon coordinations of the Zintl phases Eu₂Si, Eu₅Si₃, EuSi, and EuSi₂ are compared.