High‐Pressure Synthesis and Physical Properties of the Europium‐Substituted Barium Clathrate Ba8−xEuxGe43□3 (x ≤ 0.6)

The new clathrate Ba_8–xEuxGe₄₃□₃ (x = 0.6) was synthesized at a pressure of 1 GPa and temperatures of up to 1220 K by means of a multi‐anvil device (Walker module) and a hydraulic 1000 ton press. X‐ray powder diffraction data indicate that the crystal structure of Ba_8–xEuxGe₄₃□₃ (x = 0.6, space group , a = 21.2588(3) Å) corresponds to that of Ba₈Ge₄₃□₃. Measurements of the magnetic susceptibility of Ba_8–xEuxGe₄₃□₃ reveal Curie‐paramagnetic behaviour and prove that the electronic state of europium corresponds to 4f⁷, i.e., Eu²⁺. Electrical resistivity shows a metal‐like temperature dependence and ρ(300) ≈ 2mΩ cm for x = 0.6. Heat capacity measurements reveal an upturn of c_p/T(T) below 7 K that is attributed to magnetic interaction of the europium ions.     

Quaternary Germanides Formed in Molten Aluminum: Tb2NiAl4Ge2 and Ce2NiAl6‐xGe4‐y (x ∼ 0.24, y ∼ 1.34)

The intermetallic phases Tb₂NiAl₄Ge₂ and Ce₂NiAl_6‐xGe_4‐y (x ∼ 0.24, y ∼ 1.34) were synthesized in molten Al at temperatures below 1000 °C. Both compounds adopt the tetragonal space group I4/mmm with cell parameters of a= 4.1346(2) Å c = 19.3437(7) Å for Tb₂NiAl₄Ge₂ and a= 4.1951(9) Å and c = 26.524(7) Å for Ce₂NiAl_6‐xGe_4‐y. The Tb₂NiAl₄Ge₂ structure features NiAl₄Ge₂ layers separated by a double layer of rare earth ions. The Ce₂NiAl_6‐xGe_4‐y (x ∼ 0.24, y ∼ 1.34) structure also contains the NiAl₄Ge₂ layers along with a vacancy defect PbO‐type Al_2‐xGe_2‐y layer, and is related to the Ce₂NiGa₁₀ structure type. Ordering of vacancies cause the formation of a 3ax3b superstructure in the crystal as seen by electron diffraction experiments. Tb₂NiAl₄Ge₂ exhibits Curie‐Weiss paramagnetic behavior with an antiferromagnetic transition observed at ∼20 K. Ce₂NiAl_6‐xGe_4‐y shows a much more complex magnetic behavior possibly due to temperature induced variation in the valency of the Ce atoms.     

Cs4BiAs3Se7: A Novel Bismuth‐Selenoarsenate with Infinite [BiAs3Se7]4– Chains Containing Two Different Anions, [AsSe3]3– and trans‐[As2Se4]4–

A new phase has been prepared by methanolothermal reaction of Cs₂CO₃, BiCl₃ and Li₃AsSe₃ at 130 °C for 36 hours. Cs₄BiAs₃Se₇ ( I ) reveals the first Bi‐selenoarsenate polyanionic chain [Bi(As₂Se₄)(AsSe₃)]^4–, consisting of Bi³⁺ ions in a distorted octahedral environment of [AsSe₃]^3– and trans‐[As₂Se₄]^4– units. The latter anion consists of a central “As₂⁴⁺” dumb‐bell whereby two Se atoms are attached to each of the As atoms. Structural Data: Space Group P2₁/n, a = 13.404(4) Å, b = 23.745(8) Å, c = 13.880(4) Å, β = 99.324(6)°, Z = 8.     

The clathrate Ba8CuxGe46−x−y□y: Phase equilibria and crystal structure

Phase relations at 700 °C, 800 °C and solidus temperatures have been derived for the clathrate system Ba₈Cu_xGe_46−x−y□_y via X-ray single crystal and powder diffractometry combined with electron probe micro analysis and differential thermal analysis. The ternary clathrate phase derives from binary Ba₈Ge₄₃□₃ and extends up to x=6. Structure investigations define cubic primitive symmetry with the space group type consistent with a clathrate type I structure throughout the entire homogeneity region 0<x?6 but defect-free Ba₈Cu_xGe_46−x exists for x?5.5.     

Ferrocene compounds: methyl 1′‐aminoferrocene‐1‐carboxylate

The title compund, [Fe(C₅H₆N)(C₇H₇O₂)], features one strong intermolecular hydrogen bond of the type N—H...O=C [N...O = 3.028 (2) Å] between the amine group and the carbonyl group of a neighbouring molecule, and vice versa, to form a centrosymmetric dimer. Furthermore, the carbonyl group acts as a double H‐atom acceptor in the formation of a second, weaker, hydrogen bond of the type C—H...O=C [C...O = 3.283 (2) Å] with the methyl group of the ester group of a second neighbouring molecule at (x, −y − , z − ). The methyl group also acts as a weak hydrogen‐bond donor, symmetry‐related to the latter described C—H...O=C interaction, to a third molecule at (x, −y − , z + ) to form a two‐dimensional network. The cyclopentadienyl rings of the ferrocene unit are parallel to each other within 0.33 (3)° and show an almost eclipsed 1,1′‐conformation, with a relative twist angle of 9.32 (12)°. The ester group is twisted slightly [11.33 (8)°] relative to the cylopentadienyl plane due to the above‐mentioned intermolecular hydrogen bonds of the carbonyl group. The N atom shows pyramidal coordination geometry, with the sum of the X—N—Y angles being 340 (3)°.     

Luminescence properties of the structure built from 3‐cyano‐4‐dicyanomethylene‐5‐oxo‐4,5‐dihydro‐1H‐pyrrol‐2‐olate and caesium(I)

The structure of caesium(I) 3‐cyano‐4‐dicyanomethylene‐5‐oxo‐4,5‐dihydro‐1H‐pyrrol‐2‐olate (CsA), Cs⁺·C₈HN₄O₂⁻, is related to its luminescence properties. The structure of CsA (triclinic, P) is not isomorphous with previously reported structures (monoclinic, P2₁/c) of the KA and RbA salts. Nevertheless, the coordination numbers of the metals are equal for all salts (nine). Each anion in the CsA salt is connected by pairs of inversion‐related N—H...O hydrogen bonds to another anion, forming a centrosymmetric dimer. The dimers are linked into infinite ribbons, stacked by means of π–π interactions, thus building up an anionic wall. Time‐dependent density functional theory calculations show that the formation of the dimer shifts the wavelength of the luminescence maximum to the blue region. Shortening the distance between stacked anions in the row [from 3.431 (5) Å for RbA to 3.388 (2) Å for KA to 3.244 (10) Å for CsA] correlates with a redshift of the luminescence maximum from 574 and 580 nm to 596 nm, respectively.     

Synthesis,Crystal, and Electronic Structure of the New Ternary Zintl Phase Eu2–xMg2–yGe3 (x = 0.1; y = 0.5)

The new ternary phase Eu_2–xMg_2–yGe₃ (x = 0.1, y = 0.5) was obtained by solid‐state synthesis and the structure determined by means of Single Crystal X‐ray Diffraction. The compound crystallizes with the orthorhombic space group Cmcm (no. 63) having structural features of the low‐temperature modification of LaSi. The crystal structure contains two different types of germanium anions: isolated Ge^4– and $\rm^{2}_{\infty}$ [Ge^2–x–y] chains. The cation substructure is partially disordered and is best represented assuming a split position. The chemical bonding is well represented by the Zintl‐Klemm concept. Resistivity measurements reveal that the compound is metallic. DFT band structure calculations were carried out on the ideal stoichiometric compound Eu₂Mg₂Ge₃, showing that this model (x = 0; y = 0) would be also metallic as a consequence of the ecliptic stacking of anions. Susceptibility and specific heat measurements evidence the presence of weak, and probably frustrated, antiferromagnetic interactions between disordered europium atoms.     

Electronic stabilization by occupational disorder in the ternary bismuthide Li3–x–yInxBi (x ≃ 0.14, y ≃ 0.29)

A ternary derivative of Li₃Bi with the composition Li_3–x–yIn_xBi (x ? 0.14, y ? 0.29) was produced by a mixed In+Bi flux approach. The crystal structure adopts the space group Fdm (No. 227), with a = 13.337 (4) Å, and can be viewed as a 2 × 2 × 2 superstructure of the parent Li₃Bi phase, resulting from a partial ordering of Li and In in the tetrahedral voids of the Bi fcc packing. In addition to the Li/In substitutional disorder, partial occupation of some Li sites is observed. The Li deficiency develops to reduce the total electron count in the system, counteracting thereby the electron doping introduced by the In substitution. First‐principles calculations confirm the electronic rationale of the observed disorder.     

Variationen modulo 4–4+, 4+3–3+4–, 4–5+, 5–4+4–5+4–4+ bei Seltenerdcarbidhalogeniden

The new compounds Pr₈(C₂)₄Cl₅ (1), Pr₁₄(C₂)₇Cl₉ (2), Pr₂₂(C₂)₁₁Cl₁₄ (3), Ce₂(C₂)Cl (4), La₂(C₂)Br (5), Ce₂(C₂)Br (6), Pr₂(C₂)Br (7), Ce₁₈(C₂)₉Cl₁₁ (8), and Ce₂₆(C₂)₁₃Cl₁₆ (9) were prepared by heating mixtures of LnX₃, Ln and carbon or in an alternatively way LnX₃, and “Ln₂C_3–x” in appropriate amounts for several days between 750 and 1200 °C. The crystal structures were investigated by X‐ray powder analysis (5–7) and/or single crystal diffraction (1–4, 8, 9). Pr₈(C₂)₄Cl₅ crystallizes in space group P2₁/c with the lattice parameters a = 7.6169(12), b = 16.689(2), c = 6.7688(2) Å, β = 103.94(1) °, Pr₁₄(C₂)₇Cl₉ in Pc with a = 7.6134(15), b = 29.432(6), c = 6.7705(14) Å, β = 104.00(3) °, Pr₂₂(C₂)₁₁Cl₁₄ in P2₁/c with a = 7.612(2), b = 46.127(9), c = 6.761(1) Å, β = 103.92(3) °, Ce₂(C₂)₂Cl in C2/c with a = 14.573(3), b = 4.129(1), c = 6.696(1) Å, β = 101.37(3) °, La₂(C₂)₂Br in C2/c with a = 15.313(5), b = 4.193(2), c = 6.842(2) Å, β = 100.53(3) °, Ce₂(C₂)₂Br in C2/c with a = 15.120(3), b = 4.179(1), c = 6.743(2) Å, β = 101.09(3) °, Pr₂(C₂)₂Br in C2/c with a = 15.054(5), b = 4.139(1), c = 6.713(3) Å, β = 101.08(3) °, Ce₁₈(C₂)₉Cl₁₁ in P$\bar{1}$ with a = 6.7705(14), b = 7.6573(15), c = 18.980(4) Å,α = 88.90(3) °, β = 80.32(3) °, γ = 76.09(3) °, and Ce₂₆(C₂)₁₃Cl₁₆ in P2₁/c with a = 7.6644(15), b = 54.249(11), c = 6.7956(14) Å, β = 103.98(3) ° The crystal structures are composed of Ln octahedra centered by C₂ dumbbells. Such Ln₆(C₂)‐octahedra are condensed into chains which are joined into undulated sheets. In compounds 1–4 three and four up and down inclined ribbons alternate (4₊4_–, 4₊3_–3₊4_–, 4₊4_–3₊4_–4₊3_–), in compounds 8 and 9 four and five (4₊5_–, 5₊4_–4₊5_–4₊4_–), and in compounds 4–7 one, one ribbons (1₊1_–) are present. The Ln‐(C₂)‐Ln layers are separated by monolayers of X atoms.     

[Sb11]3− and [As11]3−: Synthesis and Crystal Structure of Two New Ammoniates containing Trishomocubane‐like Polyanions

The ammoniates [K(18‐crown‐6)(NH₃)₂]₃Sb₁₁ · 5.5NH₃ ( 1 ) and [Cs(18‐crown‐6)]₂CsAs₁₁ · 8NH₃ ( 2 ) (18‐crown‐6 = 18C6: 1,4,7,10,13,16‐Hexaoxacyclooctadecan) were synthesized by either the reaction of K₃Sb₇ with SbPh₃ in liquid ammonia or by extraction of Cs₃As₁₁ with liquid ammonia. Single crystals were isolated and characterized by low temperature X‐ray structure analysis. [K(18‐crown‐6)(NH₃)₂]₃Sb₁₁ · 5.5NH₃ crystallizes in the space group with a = 13.31(2) Å, b = 15.161(2) Å, c = 22.521(3) Å, α = 99.23(1)°, β = 100.99(1)° and γ = 105.03(1)°. [Cs(18‐crown‐6)]₂CsAs₁₁ · 8NH₃ crystallizes in the monoclinic space group C2/c with a = 20.009(3) Å, b = 17.024(1) Å, c = 19.838(2) Å and β = 119.732(9)°. While 1 contains isolated [Sb₁₁]^3? anions and [K(18‐crown‐6)(NH₃)₂]⁺ complexes, cesium–arsenic contacts lead to one–dimensionally infinite chains in 2 .     

Cs2Hg27, das quecksilberreichste Amalgam – ein naher Verwandter der Bergman‐Phasen

Cs₂Hg₂₇, the Mercury‐richest Amalgam with Close Relationship to the Bergman Phases By electrolyzing a solution of cesium iodide in N,N‐dimethylformamide at 2 °C on a mercury cathode the amalgam Cs₂Hg₂₇ can be synthesized. It crystallizes in an own cubic structure type (space group , a = 16.557(4) Å). The structure can be rationalized by a system of concentrical polyhedral spheres, in close analogy to the Bergman phases.     

Synthesis and Crystal Structure of RbKLiAlF6 – the First Al‐Elpasolite with Three Different Alkali Metals

The synthesis of RbKLiAlF₆ via a sol‐gel route is described. The crystal structure has been determined using Rietveld‐refinement. It is shown that the compound crystallizes in the hexagonal 12L‐structure of the Cs₂NaCrF₆‐type (space‐group ) with a = 5.7195Å, c = 27.8655(4) Å and therefore belongs to the family of hexagonal elpasolites being the first example for an Al‐elpasolite with three different alkali metals. Further insights regarding structural details could be gained using ⁸⁷Rb MAS NMR spectroscopy.     

Über hexagonale Perowskite mit Kationenfehlstellen. XXVI. Ba12Ba2 2/3M 1/3□2O33□3 (MV = Nb,Ta) – die ersten Stapelvarianten eines rhomboedrischen 36 L-Typs

On Hexagonal Perovskites with Cationic Vacancies. XXVI. Ba₁₂Ba_{2 2/3}M _1/3□₂O₃₃□₃ (M^V = Nb, Ta) – the First Stacking Polytypes of a Rhombohedral 36 L-Type In the systems BaO? MO₅(M^V = Nb, Ta) for a Ba:M^V ratio of 2:1 polymorphism is observed. Here the low temperature modifications are described. They crystallize in a rhombohedral 36 L structure with three formula units Ba₁₂Ba_{2 2/3}M _1/3□₂O₃₃□₃ for the trigonal setting (M^V = Nb: a = 5.92₂ Å; c = 93.₂₅ Å; Ta: a = 5,92₂ Å; s = 93.4 Å).     

Synthesis and crystal structure of 10a‐oxo‐1‐phenylimino‐ 10‐propyl‐3,4,10,10a‐tetrahydro‐1H‐ 2‐thia‐4a,10‐diaza‐10aλ5‐ phospha‐phenanthren‐9‐one

The title novel fused tricyclic phosphoroheterocycle, C₁₉H₂₀N₃O₂PS, was synthesized in an excellent yield of 88.5% via the reac‐ tion of 1‐(2‐bromoethyl)‐2,3‐dihydro‐3‐propyl‐1,3,2‐benzodiazaphosphorin‐4(1H)‐one 2‐oxide with phenyl isothiocyanate, which contains the proximate imino and phosphoryl groups in the fused heterocycle. The crystallographic data analysis reveals that the title compound crystallizes into triclinic space group P with unit cell parameters: a = 9.159(3) Å, b = 10.463(4) Å, c = 10.698(4) Å, α = 88.090(6)°, β = 86.921(6)°, γ = 70.528(6)°, V = 965.0(6) ų for Z = 2 and there is a fused three‐ring in the molecule. The structure has been solved by direct methods and refined to R = 0.0424 for 2451 observed reflections with I >2 σ(I). The proximate imino and phosphoryl groups are not coplanar because both are jointly located in the fused heterocycle, thus having ring tension and this then destroys the conjugation between the CN and the PO moieties. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:671–676, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20169     

Copper(I) π‐Complexes with 2‐Butyne‐1,4‐diol. Synthesis and Crystal Structure of Na[CuCl2(HOCH2C≡CCH2OH)]·2H2O

Crystals of anionic Na[CuCl₂(HOCH₂C≡CCH₂OH)]·2H₂O π‐complex have been synthesized by interaction of 2‐butyne‐1,4‐diol with CuCl in a concentrated aqueous NaCl solution and characterized by X‐ray diffraction at 100 K. The crystals are triclinic: space group , a = 7.142(3), b = 7.703(3), c = 10.425(4) Å, α = 105.60(3), β = 99.49(3), γ = 110.43(3)°, V = 495.9(4) ų, Z = 2, R = 0.0203 for 3496 reflections. The structure is built of discrete [CuCl₂(HOCH₂C≡CCH₂OH)]^? anionic stacks and polymeric cations among the stacks. The Cu^I atom adopts trigonal planar coordination of two Cl^? anions and the C≡C bond of 2‐butyne‐1,4‐diol, Cu–(C≡C) distance is equal to 1.903(3) Å. Na⁺ cations environment is octahedral and consists of O and Cl atoms. The crystal packing is governed by strong hydrogen bonds of O–H···Cl and O–H···O types.     

Neue Germanide mit geordneter Ce3Pt4Ge6‐Struktur – Die Verbindungen Ln3Pt4Ge6 (Ln: Pr–Dy)

New Germanides with an Ordered Variant of the Ce₃Pt₄Ge₆ Type of Structure – The Compounds Ln₃Pt₄Ge₆ (Ln: Pr–Dy) Six new germanides Ln₃Pt₄Ge₆ with Ln = Pr–Dy were synthesized by heating mixtures of the elements at 900 °C, annealing the inhomogeneous powders at 1050‐1100 °C for six days and then cooling down from 700 °C in the course of two months. The crystal structures of Pr₃Pt₄Ge₆ (a = 26.131(5), b = 4.399(1), c = 8.820(2) Å), Sm₃Pt₄Ge₆ (a = 25.974(3), b = 4.356(1), c = 8.748(1) Å), and Dy₃Pt₄Ge₆ (a = 26.079(5), b = 4.311(1), c = 8.729(2) Å) were determined by single crystal X‐ray methods. The compounds are isotypic (Pnma, Z = 4) and crystallize with an ordered variant of the Ce₃Pt₄Ge₆ type of structure (Cmcm, Z = 2) consisting of CaBe₂Ge₂‐ and YIrGe₂‐analogous units. The platinum atoms are located in distorted square pyramids of germanium atoms and build up with them a three‐dimensional network. The coordination polyhedra of the platinum and germanium atoms around the rare‐earth metal atoms are pentagonal and hexagonal prisms. These are completed by some additional atoms resulting in coordination numbers of 14 and 15 respectively. The other germanides were investigated by powder methods resulting in the following lattice constants: a = 26.067(6), b = 4.388(1), c = 8.800(2) Å for Ln = Nd; a = 25.955(7), b = 4.337(1), c = 8.728(2) Å for Ln = Gd; a = 25.944(5), b = 4.322(1), c = 8.698(2) Å for Ln = Tb. The atomic arrangement of Ln₃Pt₄Ge₆ is compared with the well‐known monoclinic structure of Y₃Pt₄Ge₆.     

Tetrarubidium Nonagermanide(4–) Ethylenediamine,Rb4[Ge9][en]

Tetrarubidiumnonagermanid(4–)-ethylendiamin, Rb₄[Ge₉][en] Orange-farbene Kristalle von Rb₄[Ge₉][en] erhält man nach der Austauschreaktion einer Lösung von ,NaGe_2.25‘ (precursor) in Ethylendiamin (en) mit festem RbI bei 360 K und nachfolgender langsamer Abkühlung. Die Verbindung ist äußerst empfindlich gegen Oxidation und Hydrolyse. Der thermische Abbau im dynamischen Vakuum beginnt mit der vollständigen Abgabe von en bei 350 K. Es folgt die Sublimation von Rubidium in vier weiteren Stufen (Rb₈Ge₂₅, Rb₈Ge₄₄, Rb_xGe₁₃₆ mit x È 16, Ge). Das Ramanspektrum zeigt die charakteristischen Banden des Anions [Ge₉]^4– bei 151, 163, 185 und 222 cm^–1. Rb₄[Ge₉][en] kristallisiert in einem neuen Strukturtyp (Raumgruppe P2₁/m; a = 15.353 Å, b = 16.434 Å, c = 15.539 Å, β = 113.75°; Z = 6; Pearsonsymbol mP198-40), der als hierarchische Variante der Strukturen von Al₄YbMo₂ und CrB₄ (hierarchische Basistypen, „initiators”︁) beschrieben werden kann, indem Atome partiell durch Aggregate ersetzt werden: B₄[□][Cr] ≙ Al₄[Yb][Mo]₂ ≙ Rb₄[Ge₉][en]_1–2. Drei kristallographisch unabhängige [Ge₉]^4–-Cluster sind in ein vierbindiges 46⁵-Netz aus Rb-Atomen eingebettet, ein Netzwerk kondensierter Tetraasterane. Die Cluster sind verzerrte überkappte tetragonale Antiprismen mit D₁(Ge–Ge) = 2.57 Å (16 Ç ) und D₂(Ge–Ge) = 2.84 Å (4 Ç ). Die Atome der Cluster mit D₁ und D₂ liegen auf der Oberfläche eines Rotationsellipsoids (a = b = 2.136 Å, c = 2.431 Å). Die en-Moleküle befinden sich in offenen Kanälen entlang [1¯ 0 1]. Die Koordinationen [Ge₉]Rb_12/4 und Rb [Ge₉]_4/12 en_2/8 zeigen, daß beim ersten Schritt der Solvatisierung Kationen und Clusteranionen nicht voneinander getrennt werden.     

Na6Si2O7 – The Missing Structural Link among Alkali Pyrosilicates

The crystal structure of sodium pyrosilicate (Na₆Si₂O₇) was solved from single crystal diffraction data and refined to an R index of 0.051 for 17034 independent reflections. The compound is triclinic with space group P (a = 5.8007(8) Å, b = 11.5811(15) Å, c = 23.157(3) Å, α = 89.709(10)°, β = 88.915(11)°, γ = 89.004(11)°, V = 1555.1(4) Å³, Z = 8, D_x = 2.615 g · cm^–3, μ(Mo‐K_α) = 7.94 cm^–1). A characteristic feature of the crystals is a twinning by reticular pseudo‐merohedry, which simulates a much larger monoclinic C centered lattice (V′ = 6220 Å³, Z = 32). The twin element corresponds to a twofold rotation axis running parallel to the [0 direction of the triclinic cell. The compound belongs to the group of sorosilicates, i.e. it is based on [Si₂O₇] groups, which are arranged in layers parallel to (100). Charge compensation within the structure is accomplished by monovalent sodium cations distributed among 24 crystallographically independent positions. They are coordinated by four to six nearest oxygen neighbors. Most of the coordination polyhedra can be approximately described as distorted tetrahedra or tetragonal pyramids. An alternative understanding of Na₆Si₂O₇ can be gained if the tetrahedrally coordinated sodium atoms are considered for the construction of a framework. Actually, each four of the dimers within a single slice are linked by a more or less distorted [NaO₄] tetrahedron. The resulting structural motif is similar to the one that can be observed in melilites, where linkage between the T₂O₇ (T: Al, Si) moieties is provided by [MgO₄]‐ (as in akermanite, Ca₂Mg[Si₂O₇]) or [AlO₄] tetrahedra (as in gehlenite, Ca₂Al[AlSiO₇]). By sharing common edges, the [NaO₄] tetrahedra in Na₆Si₂O₇ are forming columns running parallel to 25 . The resulting framework contains tunnels in which the more irregularly coordinated sodium cations are incorporated.     

Cs3UP2S8, a Coordination Polymer Containing the Unprecedented [U=S]2+ Sulfidouranium(2+) Moiety

Although terminal chalcogeno ligands are well known for the group 5 and 6 transition metals, they are highly unusual for the oxophilic group 4 metals and unknown so far for the lanthanides or actinides. Cs₃UP₂S₈, is the first actinide compound containing a terminal M=S group. It was synthesized by reacting uranium metal, Cs₂S, S, and P₂S₅ in a 4:1:8:3 ratio at 700 °C in an eutectic LiCl/CsCl mixture. The crystal structure was determined by single‐crystal X‐ray diffraction techniques. Cs₃UP₂S₈ crystallizes in the rhombohedral space group R$\bar{3}$ [a = 15.5217(8) Å; c = 35.132(2) Å, V = 8305.0(8) ų, Z = 18]. The crystal structure is based on a tetrahedral network type, wherein the uranium atoms are coordinated by a unusual sulfido moiety and thiophosphate groups in a pseudo‐tetrahedral fashion. The U=S distance of 2.635(3) Å observed in the sulfide moiety is approx. 0.2 Å shorter than the average U–S single bond length, indicating a double‐bond type character.