The New Cesium Praseodymium Thiophosphate Cs3Pr5[PS4]6

Transparent platelet‐shaped green single crystals of the title compound were obtained by the reaction of cesium bromide, praseodymium, sulfur, and red phosphorus in the molar ratio 1:2:8:2 with an excess of CsBr as flux in evacuated silica ampoules at 950 °C for fourteen days. Cs₃Pr₅[PS₄]₆ crystallizes monoclinically in the space group C2/c (a = 1627.78(7), b = 1315.09(6), c = 2110.45(9) pm, β = 103.276(5)°; Z = 4). Its crystal structure is different from all the other alkali‐metal containing ortho‐thiophosphates of the lanthanides, since it is not possible to formulate a layer containing the praseodymium centered sulfur polyhedra ([PrS₈]^13—, d(Pr—S) = 286 — 307 pm) and the isolated [PS₄]^3— tetrahedra (d(P—S) = 202 — 207 pm, ?(S—P—S) = 104 — 106°). All these tetrahedra are edge‐sharing with the metal polyhedra to build up a framework instead. The coordination sphere of the half occupied (Cs2)⁺ cations (CN = 10 + 2) can be described as two six‐membered sulfur rings in chair conformation containing a “cesium‐pair” in the middle. In contrast the (Cs1)⁺ cations are surrounded in the not unusual configuration of tetracapped trigonal prisms (CN = 10, better 10 + 2 as well).     

Einkristalle von CuPrS2 im A— und Pr2S3 im C—Typ bei Versuchen zur Synthese ternärer Kupfer(I)—Praseodym(III)—Sulfide

Single Crystals of A—type CuPrS₂ and C—type Pr₂S₃ from Attempts to Synthesize Ternary Copper(I) Praseodymium(III) Sulfides Coarse, yellowish‐green single crystals of the ternary copper(I) praseodymium(III) sulfide CuPrS₂ form within seven days at 800°C by oxidation of elemental copper and praseodymium with sulfur (molar ratio: 1:1:2) in evacuated silica tubes when equimolar quantitites of CsCl are present as flux. Attempts to synthesize CuPr₃S₅ or CuPr₅S₈ under analogous conditions always yield two‐component mixtures of CuPrS₂ and Pr₂S₃ (C type) instead of the desired target compounds. The crystal structure of CuPrS₂ (monoclinic, P2₁/c; a = 655.72(6), b = 722.49(6), c = 686.81(6)pm, β = 98.686(7)°; Z = 4) exhibits undulated layers {[Cu(S1)_3/3(S2)_1/1]^3—} parallel (100) which consist of vertex‐linked pairs of two [CuS₄]^7— tetrahedra ([Cu₂S₆]^10—) sharing a common edge. Their three‐dimensional cross‐linkage is achieved by Pr³⁺ cations in monocapped trigonal prismatic coordination of seven S^2— anions each. The metal sulfur distances in the [CuS₄] units cover with 233 (Cu—S2) and 236 (Cu—S1) as well as 247 (Cu—S1′) and 248pm (Cu—S1″) a rather broad interval, whereas those (Pr—S: 284—304 pm) within the [PrS₇] polyhedra lie relatively closer together. According to Pr_2.677□_0.333S₄ (with Z = 4), C—Pr₂S₃ crystallizes in a cation‐deficient Th₃P₄‐type structure (cubic, I4¯3d; a = 857.68(7) pm; Z = 5.333 for Pr₂S₃). In conformity with the Niggli formula {PrS_8/5.333} Pr³⁺ is surrounded trigon‐dodecahedrally by eight S^2— at distances of 287 (4×) and 307pm (4×). Neither the X‐ray single‐crystal structure refinement nor electron‐beam microprobe analyses leave any evidence for the incorporation of Cu⁺ cations into this crystal structure.     

Na2ZrS3: Ein ternäres Sulfid des Zirconiums mit aufgefüllter AlCl3‐Struktur

Na₂ZrS₃: A Ternary Zirconium Sulfide with Stuffed AlCl₃‐type Structure Dark green, plate‐like single crystals of Na₂ZrS₃ (monoclinic, C2/m; a = 664.69(6), b = 1152.5(1), c = 695.48(7) pm, β = 108.78(1)°; Z = 4) are obtained along with pale yellow platelets of NaZr₂N₂SCl (trigonal, R3m; a = 363.56(3), c = 2951.2(4) pm; Z = 3) upon oxidation of zirconium metal with sulfur and sodium azide (NaN₃) in the presence of fluxing NaCl (molar ratio 7:6:2:3) in evacuated silica tubes at 850°C within three weeks. The crystal structure is best described as stuffed AlCl₃ type with all cations (Na⁺ and Zr⁴⁺) in octahedral coordination of the S^2– anions, which build up a cubic closest packed host lattice. The internuclear metal sulfur distances range from 276 to 296 pm for all three crystallographically different Na⁺ cations, and from 258 to 260 pm for Zr⁴⁺.     

Rb6LiPr11Cl16[SeO3]12: Ein chloridisch derivatisiertes Rubidium‐Lithium‐Praseodym(III)‐Oxoselenat(IV)

Rb₆LiPr₁₁Cl₁₆[SeO₃]₁₂: A Chloride‐Derivatized Rubidium Lithium Praseodymium(III) Oxoselenate(IV) Transparent green square platelets with often truncated edges and corners of Rb₆LiPr₁₁Cl₁₆[SeO₃]₁₂ were obtained by the reaction of elemental praseodymium, praseodymium(III,IV) oxide and selenium dioxide with an eutectic LiCl–RbCl flux at 500 °C in evacuated silica ampoules. A single crystal of the moisture and air insensitive compound was characterized by X‐ray diffraction single‐crystal structure analysis. Rb₆LiPr₁₁Cl₁₆[SeO₃]₁₂ crystallizes tetragonally in the space group I4/mcm (no. 140; a = 1590.58(6) pm, c = 2478.97(9) pm, c/a = 1.559; Z = 4). The crystal structure is characterized by two types of layers parallel to the (001) plane following the sequence 121′2′1. Cl^? anions form cubes around the Rb⁺ cations (Rb1 and Rb2; CN = 8; d(Rb⁺?Cl^?) = 331 – 366 pm) within the first layer. One quarter of the possible places for Rb⁺ cations within this CsCl‐type kind of arrangement is not occupied, however the Cl^? anions of these vacancies are connected to Pr³⁺ cations (Pr4) above and below instead, forming square antiprisms of [(Pr4)O₄Cl₄]^9? units (d(Pr4?O) = 247–249 pm; d(Pr4?Cl) = 284–297 pm) that work as links between layer 1 and 2. Central cations of the second layer consist of Li⁺ and Pr³⁺. While the Li⁺ cations are surrounded by eight O^2? anions (d(Li?O5) = 251 pm) in the shape of cubes again, the Pr³⁺ cations are likewisely coordinated by eight O^2? anions as square antiprisms (for Pr1, d(Pr1?O2) = 242 pm) and by ten O^2? anions (for Pr2 and Pr3), respectively. The latter form tetracapped trigonal antiprisms (Pr2, d(Pr2?O) = 251–253 pm and 4 × 262 pm) or bicapped distorted cubes (Pr3, d(Pr3?O) = 245–259 pm and 2 × 279 pm). The non‐binding electron pairs (“lone pairs”) at the two crystallographically different Ψ¹‐tetrahedral [SeO₃]^2? anions (d(Se⁴⁺?O^2?) = 169–173 pm) are directing towards the empty cavities between the layer‐connecting [(Pr4)O₄Cl₄]^9? units.     

Three Modifications of [Pr2(ClO4)2(H2I2O10)]·8 H2O — A Theme with Variations

From solutions containing praseodymium perchlorate and periodic acid, three different modifications of [Pr₂(ClO₄)₂(H₂I₂O₁₀)] · 8 H₂O could be obtained. All of them crystallize in the monoclinic system, space group P2₁/c (α: a = 1091.47(6), b = 728.24(4), c = 1388.84(8) pm, β = 101.420(3)°; β: a = 1169.93(3), b = 728.72(2), c = 1384.50(4) pm, β = 112.303(2)°; γ: a = 1209.56(4), b = 712.53(2), c = 1361.64(5) pm, β = 115.691(1)°). The structures contain Pr³⁺ cations which are coordinated by [H₂I₂O₁₀]^4— anions yielding two‐dimensional networks. These networks are separated by ClO₄^— anions yielding a layered structure.     

Strukturchemische und impedanzspektroskopische Untersuchungen an Mg2+-stabilisierten Na+/Pr3+-β″-Al2O3-Kristallen

Structural Chemistry and Impedance Spectroscopy of Mg²⁺ stabilized Na⁺/Pr³⁺-β″-Aluminas The structure with the ionic distribution in the conduction planes of a Pr³⁺-exchanged Mg²⁺ stabilized Na⁺-β″-alumina crystal, composition determined by electron microprobe analysis to Na_1.19Pr_0.13Mg_0.49Al_10.49O₁₇ (degree of exchange ξ = 25%, related to Na⁺ content), has been investigated by single crystal X-ray diffraction methods at room temperature (R3 m, Z = 3, a = 561.8(2) pm, c = 3 361.5(11) pm). Pr³⁺ is slightly shifted in the ab-plane from the centrosymmetric 9 d (mO) into a 18 h site. Na⁺ occupies 18 h as well as 6 c (BR) positions. Ionic conductivity data of Mg²⁺ stabilized Na⁺/Pr³⁺-β″-Al₂O₃ crystals with varying degree of exchange determined by impedance spectroscopy are given in an Arrhenius diagram. With growing Pr³⁺ content the conductivity σ decreases with increasing activation energy.     

Synthesen und Kristallstrukturen von neuen Alkalimetall‐Selten‐Erd‐Telluriden der Zusammensetzungen KLnTe2 (Ln = La,Pr, Nd,Gd), RbLnTe2 (Ln = Ce,Nd) und CsLnTe2 (Ln = Nd)

Syntheses and Crystal Structures of New Alkali Metal Rare‐Earth Tellurides of the Compositions KLnTe₂ (Ln = La, Pr, Nd, Gd), RbLnTe₂ (Ln = Ce, Nd) and CsLnTe₂ (Ln = Nd) Of the compounds ALnQ₂ (A = Na, K, Rb, Cs; Ln = rare earth‐metal; Q = S, Se, Te) the crystal structures of the new tellurides KLaTe₂, KPrTe₂, KNdTe₂, KGdTe₂, RbCeTe₂, RbNdTe₂, and CsNdTe₂ were determined by single‐crystal X‐ray analyses. They all crystallize in the α‐NaFeO₂ type with space group R3¯m and three formula units in the unit cell. The lattice parameters are: KLaTe₂: a = 466.63(3) pm, c = 2441.1(3) pm; KPrTe₂: a = 459.73(2) pm, c = 2439.8(1) pm; KNdTe₂: a = 457.83(3) pm, c = 2443.9(2) pm; KGdTe₂: a = 449.71(2) pm, c = 2443.3(1) pm; RbCeTe₂: a = 465.18(2) pm, c = 2533.6(2) pm; RbNdTe₂: a = 459.80(3) pm, c = 2536.5(2) pm, and CsNdTe₂: a = 461.42(3) pm, c = 2553.9(3) pm. Characteristics of the α‐NaFeO₂ structure type as an ordered substitutional variant of the rock‐salt (NaCl) type are layers of corner‐sharing [(A⁺/Ln³⁺)(Te^2—)₆] octahedra with a layerwise alternating occupation by the cations A⁺ and Ln³⁺.     

The Crystal Structure of Solvent‐Free Silver Dodecachloro‐closo‐dodecaborate Ag2[B12Cl12] from Aqueous Solution

Colourless octahedral single crystals of solvent‐free Ag₂[B₁₂Cl₁₂] (cubic, Pa3¯; a = 1238.32(7) pm, Z = 4) are obtained by the metathesis reaction of Cs₂[B₁₂Cl₁₂] with an aqueous solution of silver nitrate (AgNO₃) and recrystallization of the crude product from water. The crystal structure is best described as a distorted anti‐CaF₂‐type arrangement in which the quasi‐icosahedral [B₁₂Cl₁₂]^2— anions (d(B—B) = d(B—Cl) = 177—180 pm) are arranged in a cubic closest‐packed fashion. The tetrahedral interstices are filled with Ag⁺ cations which are strongly displaced from their ideal positions. Thereby each silver atom gets coordinated by six chlorine atoms from the edges of three [B₁₂Cl₁₂]^2— anions providing a distorted octahedral coordination sphere to the Ag⁺ cations (d(Ag—Cl) = 283—285 pm, CN = 6).     

PrSeTe2, ein geordnetes ternäres Polychalkogenid mit NdTe3‐Struktur

PrSeTe₂, an Ordered Ternary Polychalcogenid with NdTe₃ Structure Single crystals of PrSeTe₂ have been obtained by reaction of the elements in a LiCl/RbCl flux at 970 K during 7 days. PrSeTe₂ crystallizes in space group Cmcm (No. 63), with four formula units per unit cell. The lattice constants are a = 426.1(1) pm, b = 2506.0(5) pm, and c = 426.0(1) pm. The crystal structure is an ordered ternary variant of the NdTe₃ type. It consists of a puckered double layer of praseodymium and selenium atoms [PrSe] sand wiched by two square planar layers of tellurium atoms [Te] yielding a stacking —[Te]—[Te]—[PrSe]— along [010]. The Te atoms build regular 4⁴ nets with Te—Te distances of 301, 3(1) pm. DFT calculations propose that this compounds should be metallic mainly due to contributions of the Pr f‐electrons. The band structure shows no significance for a distortion in the [Te]—nets.     

Zwei Formen (A- und B-Typ) von Pr2Te[SiO4]

Two Types (A and B) of Pr₂Te[SiO₄] Two forms of praseodymium(III) telluride ortho-silicate (Pr₂Te[SiO₄]) are obtained as light green, transparent single crystals (A type: bricks, B type: needles, both unsensitive to hydrolysis) from a CsCl melt by reacting Pr, TeO₂ and SiO₂ in stoichiometric ratios (950 °C, 10 d) in evacuated silica tubes. A-Pr₂Te[SiO₄] crystallizes orthorhombically (Pbcm; a = 633.70(3), b = 724.42(4), c = 1125.13(8) pm; Z = 4) with alternatingly arranged monolayers {(Pr2)Te}⁺ and {(Pr1)[SiO₄]}^– parallel (001). Pr1 exhibits a coordination number of nine (6 O and 3 Te) while Pr2 has ten next neighbours (6 O and 4 Te), in which all the oxygen atoms are components of discrete ortho-silicate tetrahedra ([SiO₄]^4–), as also is the case in the B-type structure. The telluride anions show coordination numbers of seven (3 Pr1 and 4 Pr2). B-Pr₂Te[SiO₄] crystallizes monoclinically (P2₁/c; a = 989.90(7), b = 648.03(4), c = 870.68(6) pm, β = 94.307(8)°; Z = 4) with along [100] alternatingly sheethed double layers [{(Pr1)Te}₂]²⁺ and [{(Pr2)[SiO₄]}₂]^2–. This results in coordination numbers of eight (4 O and 4 Te) for Pr1, nine plus one (8 O and 1 + 1 Te) for Pr2, and five plus one (4 Pr1 and 1 + 1 Pr2) for Te. The almost 8% higher density of Pr₂Te[SiO₄] in the A-type structure (D_x = 6.45 g/cm³) compared to that of B-type Pr₂Te[SiO₄] (D_x = 5.98 g/cm³) is quite remarkable.     

Pr2Br5: No mixed valence praseodymium bromide

The metallothermic reduction of praseodymium tribromide, PrBr₃, with lithium metal (molar ratio 1:1) in sealed tantalum containers at 850°C yields bronze lustrous rods of Pr₂Br₅. The crystal structure (monoclinic, P2₁/m, Z = 2, a = 774.38(4), b = 415.33(3), c = 1327.06(9) pm, β = 90.816(6)°, V_m = 128.52(2) cm³ mol^?1) contains seven- and eight-coordinate trivalent praseodymium in mono- and bicapped trigonal prisms. Pr₂Br₅ should therefore be formulated as (Pr³⁺)₂(Br^?)₅(e^?). It is isostructural with Pr₂I₅ and is believed to be identical with PrBr_2,38 reported for the Pr/PrBr₃ system.     

Thiosilicate der Selten‐Erd‐Elemente: II. Die nichtzentrosymmetrischen Caesium‐Derivate CsM[SiS4] (M = Sm — Tm)

Thiosilicates of the Rare‐Earth Elements: II. The Noncentrosymmetric Cesium Derivatives CsM[SiS₄](M = Sm — Tm) The cesium lanthanoid thiosilicates CsM[SiS₄] (M = Sm — Tm) all crystallize orthorhombically in the noncentrosymmetric space group P2₁2₁2₁ with four formula units per unit cell. The lattice constants show values within the following ranges: a = 630 — 640 pm, b = 665 — 673 pm and c = 1763 — 1778 pm. The reaction of lanthanoid metal (M) with sulfur (S) and silicon disulfide (SiS₂) with an excess of cesium chloride (CsCl) serving both as flux medium and as reactand (Cs⁺ source) in evacuated silica ampoules for seven days at 850 °C leads to air‐ and water‐resistant platelet‐shaped single crystals that exhibit the colour of the lanthanoid trication (M³⁺) with a slight yellowish shade. The crystal structure arranges in layers since anionic {M[SiS₄]}^— sheets get alternatingly piled with those of Cs⁺ cations. The M³⁺ cations are surrounded capped trigonal prismatically by seven sulfide anions whereas the Cs⁺ cations have an environment of nine plus two S^2— in the shape of a fivefold overcapped trigonal prism. All sulfide anions belong to almost ideal tetrahedral ortho‐thiosilicate units [SiS₄]^4—.     

Synthese,Kristallstruktur und Magnetismus von [(CH3)2NH2][PrCl4(H2O)2]

Preparation, Crystal Structure, and Magnetism of [(CH₃)₂NH₂][PrCl₄(H₂O)₂] The complex water containing chloride [(CH₃)₂NH₂][PrCl₄(H₂O)₂] has been prepared for the first time and the crystal structure has been determined from single crystal X‐ray diffraction data. The compound crystallizes orthorhombically in the space group Cmca (Z = 8) with a = 1796.6(2) pm, b = 940.7(1) pm, and c = 1238.4(2) pm. The anionic part of the structure is built up by chains of edge‐connected trigondodecahedra [PrCl₆(H₂O)₂]^3– according to [PrCl_4/2Cl₂(H₂O)₂]^–, which are held together by dimethylammonium cations ([(CH₃)₂NH₂]⁺). In order to study the interactions between the praseodymium cation (Pr³⁺) and the ligands magnetic measurements were carried out. The magnetic data were interpreted by ligand field calculations applying the angular overlap model.     

BaClSCN und Na4Mg(SCN)6: Zwei neue wasserfreie Thiocyanate der Erdalkalimetalle

BaClSCN and Na₄Mg(SCN)₆: Two New Thiocyanates of the Alkaline Earth Metals The reaction of BaCl₂ and NaSCN yielded single crystals of BaClSCN (P 2₁/m, Z = 2, a = 588.6(1) pm, b = 465.8(1) pm, c = 864.4(2) pm, β = 100.20(3)°, R_all = 0.0214). According to X‐ray single crystal investigations, the structure consists of anionic SCN^– and Cl^– layers, respectively, alternating in [001] direction. The SCN^–‐ions are connected via the N and the S atoms to the cations. Na₄Mg(SCN)₆ (P 3 1c, Z = 2, a = 863.8(1) pm, c = 1399.3(2) pm, R_all = 0.0870), which was obtained from a melt of NaSCN and MgCl₂, consists of anionic layers with the cations between the sheets. The holes are filled altenatingly by Na⁺ or Na⁺ and Mg²⁺. Regarding only the C‐atoms of the SCN^– group, the structure can be described as a hexagonal closest packing whith the cations occupying 5/6 of the octahedral voids.     

NaPr9S2[SiO4]6: Ein Sulfidsilicat des Praseodyms mit Bromapatitstruktur

NaPr₉S₂[SiO₄]₆: A Sulfide Silicate of Praseodymium with the Structure of Bromapatite NaPr₉S₂[SiO₄]₆ is obtained as pale green single crystals of hexagonal columnar shape from reactions of Pr, Pr₆O₁₁, S, SiO₂ and NaCl (850°C, 7 d) in fused evacuated silica tubes. The crystal structure (hexagonal, P6₃/m, Z = 1, a = 981.05(4), c = 689.68(2) pm) corresponds with a modified bromapatite structure where orthosilicate ([SiO₄]^4?) and sulfide (S^2?) anions provide coordination numbers of eight and nine to the two crystallographically different cations. These occupy the positions 4 f (Na⁺ together with Pr³⁺ in a molar ratio of 1:3) and 6h (Pr³⁺ only) to realize an average Ca₅Br[PO₄]₃-type structure.     

HoClTe2O5: Ein tellurdioxidreiches Holmium(III)‐Chlorid‐Oxotellurat(IV)

HoClTe₂O₅: A Telluriumdioxide‐rich Holmium(III) Chloride Oxotellurate(IV) While attempting to synthesize anionically derivatized holmium oxotellurates by reacting holmium chloride (HoCl₃) with tellurium oxide (TeO₃; molar ratio 1 : 3, 800°C 10 d) in evacuated silica ampoules, transparent, greenish yellow and coarse single crystals of holmium(III) chloride oxotellurate(IV) HoClTe₂O₅ (triclinic, P1; a = 762.07(6), b = 796.79(6), c = 1010.36(8) pm, α = 100.987(4), ß = 99.358(4), γ = 91.719(4)°; Z = 4) were obtained. The crystal structure contains eightfold coordinated (Ho1)³⁺ (only surrounded by oxygen atoms) and sevenfold coordinated (Ho2)³⁺ cations (surrounded by one chloride and six oxide anions). Each sort of holmium polyhedra convenes independently to chains along [100] by edge‐sharing which again combine alternately via O6 and O9 to form ²{[Ho₂O₁₀(Cl1)]^15—} layers parallel (001). Each of the four crystallographically different Te⁴⁺ cations are surrounded by three close oxygen atoms (d(Te—O) = 188 — 195 pm) and always one more situated further away. The stereochemical activity of the non‐bonding electron pairs (“lone pairs”) leads to ψ¹‐trigonal bipyramidal coordination figures. The ψ¹‐tetrahedral [TeO₃]^2— basic units form discrete [Te₂O₅]^2— doubles with ecliptic conformation which are arranged in a fish‐bone pattern parallel to (001) on both sides of the ²{[Ho₂O₁₀Cl]^15—} layers. The coherence of the ²{[Ho₂(Cl1)Te₄O₁₀]⁺} layers is exclusively maintained via Cl2—Te1 contacts with an extraordinary long distance of 335 pm. As (Cl1)^— belongs to the coordination sphere of (Ho2)³⁺ and (Cl2)^— is only surrounded by Te⁴⁺, the compound should be correctly named holmium(III) chloride oxochlorotellurate(IV) Ho₂Cl[Te₄O₁₀Cl] (Z = 2).     

Single Crystals of C–La2Se3, C–Pr2Se3, and C–Gd2Se3 with Cation‐Deficient Th3P4‐Type Structure

Ruby‐red, bead‐shaped single crystals of C‐type La₂Se₃ (a = 905.21(6) pm), Pr₂Se₃ (a = 891.17(6) pm), and Gd₂Se₃ (a = 872.56(5) pm) are obtained by oxidation of the respective rare‐earth metal (M = La, Pr and Gd) with selenium (molar ratio 2 : 3) in evacuated silica tubes at 750 °C in the presence of fluxing CsCl within seven days. Their crystal structure belongs to a cation‐deficient Th₃P₄‐type variant (cubic, I 4 3d) according to M_2.667□_0.333Se₄ (Z = 4) or M₂Se₃ (Z = 5.333) offering coordination numbers of eight (Se^2– arranged as trigonal dodecahedra) to the M³⁺ cations. In spite of the high Cs⁺ activity in molten CsCl, no cesium incorporation into the M_5.333□_0.667Se₈‐frame structure (e. g. as CsM₅Se₈ with Z = 2) could be achieved, judged from both results of electron beam X‐ray microanalyses and refined occupation factors of the metal position very close to x = 8/9 for M_3xSe₄.     

Vier Oxidselenide des Praseodyms: Pr10OSe14, Pr2OSe2, Pr2O2Se und Pr4O4Se3

Four Oxyselenides of Praseodymium: Pr₁₀OSe₁₄, Pr₂OSe₂, Pr₂O₂Se, and Pr₄O₄Se₃ By reacting elemental praseodymium with selenium and selenium dioxide (SeO₂) as oxygen source in suitable stoichiometric ratios, it is possible to prepare the single‐phase praseodymium(III) oxyselenides Pr₁₀OSe₁₄, Pr₂OSe₂, Pr₂O₂Se, and Pr₄O₄Se₃ each within seven days at 750 °C in torch‐sealed evacuated silica tubes. The addition of equimolar amounts of CsCl as flux guarantees quick and complete reactions to single‐crystalline, water‐ and air‐resistant products. Pr₁₀OSe₁₄ (tetragonal, I4₁/acd; a = 1568.74(8), c = 2073.4(1) pm; Z = 8) crystallizes as dark‐red polyhedra. Pr₂OSe₂ (monoclinic, P2₁/c; a = 882.05(6), b = 732.89(5), c = 732.94(5) pm, β = 100.288(7)°; Z = 4) and Pr₂O₂Se (trigonal, P3m1; a = 401.12(3), c = 705.51(5) pm; Z = 1) accumulate as yellowish green platelets with rectangular and hexagonal cross‐sections, respectively. Pr₄O₄Se₃ (orthorhombic, Amm2; a = 849.92(6), b = 402.78(3), c = 1292.57(9) pm; Z = 2) forms lath‐shaped, pleochroitic crystals with a strong tendency for twinning, which appear green along [001], but red along [100] and [010]. All the crystal structures of these oxyselenides are dominated by [OPr₄] tetrahedra, whose condensation rate strongly increases with growing oxygen content. Se^2– anions, in the case of Pr₄O₄Se₃ (≡ {(Pr³⁺)₄(O^2–)₄(Se^2–)[Se₂]^2–}) as well as [Se₂]^2– dumb‐bells, take care of charge balance and threedimensional cross‐linkage. In the oxygen‐poor Pr₁₀OSe₁₄ the [OPr₄]¹⁰⁺ tetrahedra occur isolated and are embedded in the complex anionic matrix framework {(Pr₆Se₁₄)^10–}. The oxygen‐rich links in this row show according to {[OPr_3/3Pr_1/1]}Se₂ (≡ Pr₂OSe₂), {([OPr_4/4]₂)}Se (≡ Pr₂O₂Se), and {([OPr_4/4]₄)}[Se₂]Se (≡ Pr₄O₄Se₃) [OPr₄] tetrahedra which are connected to more or less dense layers via corners and respectively one, three and four common edges.     

Über Oxidtelluride (M2O2Te) der leichten Lanthanide (M = La–Nd,Sm–Ho) im A-Typ mit anti-ThCr2Si2-Struktur

On Oxytellurides (M₂O₂Te) of the Early Lanthanides (M = La–Nd, Sm–Ho) with A- or anti -ThCr₂Si₂-Type Crystal Structure By reacting elementary lanthanide metal (M = La–Nd, Sm–Ho) with tellurium dioxide (TeO₂) in a 2 : 1 molar ratio, it is possible to obtain pure and single-phase oxytellurides of the composition M₂O₂Te at 750 °C in evacuated silica tubes within a few days. When larger quantities of cesium chloride (CsCl) are added as flux, plate-like single crystals with square cross-section are formed which are not sensitive to hydrolysis and very suitable for crystal structure refinements from X-ray data. In the anti-ThCr₂Si₂ analogous crystal structure (tetragonal, I4/mmm, Z = 2; La₂O₂Te: a = 412.31(4), c = 1309.6(1) pm; Ce₂O₂Te: a = 408.17(4), c = 1294.7(1) pm; Pr₂O₂Te: a = 405.62(4), c = 1285.8(1) pm; Nd₂O₂Te: a = 403.08(4), c = 1277.1(1) pm; Sm₂O₂Te: a = 399.83(4), c = 1265.5(1) pm; Eu₂O₂Te: a = 397.56(4), c = 1257.9(1) pm; Gd₂O₂Te: a = 396.20(4), c = 1253.2(1) pm; Tb₂O₂Te: a = 393.89(4), c = 1245.4(1) pm; Dy₂O₂Te: a = 392.34(4), c = 1240.3(1) pm; Ho₂O₂Te: a = 390.57(6), c = 1239.0(3) pm) the M³⁺ cations are surrounded by nine anions (4 O^2– und 4 + 1 Te^2–) in the shape of a capped square antiprism. The anions show coordination numbers of four (O^2–: tetrahedra) and eight plus two (Te^2–: bicapped cubes) with respect to the cations. PbO-analogous square {[OM_4/4]₂}²⁺ triple layer slabs are present parallel (001), which originate through two-dimensional infinite linking of [OM₄]¹⁰⁺ tetrahedra via two trans-orientated pairs of edges (i. e. four edges altogether). These cationic layers are piled alternatingly along [001] with likewise quadratic single layers of Te^2– anions, which take care of the three-dimensional coherence as well as of the charge balance.