Thiosilicate der Selten‐Erd‐Elemente: III. KLa[SiS4] und RbLa[SiS4] – Ein struktureller Vergleich

Thiosilicates of the Rare‐Earth Elements: III. KLa[SiS₄] and RbLa[SiS₄] – A Structural Comparison Pale yellow, platelet shaped, air‐ and water resistant single crystals of KLa[SiS₄] derived from the reaction of lanthanum (La) and sulfur (S) with silicon disulfide (SiS₂) in a molar ratio of 2 : 3 : 1 with an excess of potassium chloride (KCl) as flux and source of potassium ions in evacuated silica ampoules at 850 °C within seven days. The analogous reaction utilizing a melt of rubidium chloride (RbCl) instead also leads to yellow comparable single crystals of RbLa[SiS₄]. The potassium lanthanum thiosilicate crystallizes monoclinically with the space group P2₁/m (a = 653.34(6), b = 657.23(6), c = 867.02(8) pm, β = 107.496(9)°) and two formula units per unit cell, while the rubidium lanthanum thiosilicate has to be assigned orthorhombically with the space group Pnma (a = 1728.4(2), b = 667.23(6), c = 652.89(6) pm) and four formula units in its unit cell. In both compounds the La³⁺ cations are surrounded by 8+1 sulfide anions in the shape of tricapped trigonal prisms. The Rb⁺ cations in RbLa[SiS₄] show a coordination number of 9+2 relative to the S^2? anions, which form pentacapped trigonal prisms about Rb⁺. This coordination number, however, is apparently too high for the K⁺ cations in KLa[SiS₄], so that they only exhibit a bicapped trigonal prismatic environment built up by eight S^2? anions. The isolated thiosilicate tetrahedra [SiS₄]^4? of the rubidium compound are surrounded by La³⁺ both edge‐ and face‐capping, but terminal as well as edge‐ and face‐spanning by Rb⁺. In the potassium compound there is no change for the La³⁺ environment about the [SiS₄]^4? tetrahedra, but the K⁺ cations are only able to attach terminal and via edges. The whole structure is built up by anionic equation/tex2gif-stack-1.gif{La[SiS₄]}^? layers that are separated by the alkali metal cations. In direct comparison the two thiosilicate structures can be regarded as stacking variants.     

Magnetism of the praseodymium halide thiosilicates Pr3X[SiS4]2 (X=Cl, Br, I)

The magnetism of the three compounds Pr₃X[SiS₄]₂ (X=Cl, Br, I) has been measured in the temperature range between 1.7 and 300 K. For the theoretical calculations to interpret the magnetic behavior the angular overlap model was employed to reproduce the ligand field influence and the molecular field approach to take magnetic interaction into account.     

Synthese und Kristallstrukturen von Ln3I(SiS4)2 (Ln = Pr,Nd, Sm,Tb)

Synthesis and Crystal Structures of Ln₃I(SiS₄)₂ (Ln = Pr, Nd, Sm, Tb) Single crystals of Ln₃I(SiS₄)₂ were prepared by a two‐step reaction of lanthanide metal, sulfur, silicon and iodine in the ratio 1 : 3.25 : 1 : 0.33 in quartz glass tubes. The thiosilicates crystallize in the monoclinic space group C 2/c (Z = 4) isotypic to Ce₃I(SiS₄)₂ [1]. In the crystal structures the iodide ions form chains along [001] with trigonal coordination by lanthanide ions.     

Synthese und Kristallstrukturen von Bromid—Thiosilicaten Ln3Br[SiS4]2 der Lanthanide (Ln = La,Ce, Pr,Nd, Sm,Gd)

Synthesis and Crystal Structures of Lanthanide Bromide Thiosilicates Ln₃Br[SiS₄]₂ (Ln = La, Ce, Pr, Nd, Sm, Gd) Single crystals of the bromide—thiosilicates Ln₃Br[SiS₄]₂ were prepared by reaction of lanthanide metal (Ln = La, Ce, Pr, Nd, Sm, Gd), sulfur, silicon and bromine in quartz glass tubes. The thiosilicates crystallize in the monoclinic spacegroup C2/c (Z = 4) isotypically to the iodide analogues Ln₃I(SiS₄)₂ and the A—type chloride—oxosilicates Ln₃Cl[SiO₄]₂ with the following lattice constants: La₃Br[SiS₄]₂: a = 1583.3(4) pm, b = 783.0(1) pm, c = 1098.2(3) pm, β = 97.33(3)° Ce₃Br[SiS₄]₂: a = 1570.4(3) pm, b = 776.5(2) pm, c = 1092.2(2) pm, β = 97.28(2)° Pr₃Br[SiS₄]₂: a = 1562.6(3) pm, b = 770.1(2) pm, c = 1088.9(2) pm, β = 97.50(2)° Nd₃Br[SiS₄]₂: a = 1561.4(4) pm, b = 766.0(1) pm, c = 1085.3(2) pm, β = 97.66(3)° Sm₃Br[SiS₄]₂: a = 1555.4(3) pm, b = 758.5(2) pm, c = 1079.9(2) pm, β = 98.28(2)° Gd₃Br[SiS₄]₂: a = 1556.5(3) pm, b = 750.8(1) pm, c = 1074.5(2) pm, β = 99.26(2)° In the crystal structures the bromide ions form chains along [001] with trigonal planar coordination by lanthanide cations, while the [SiS₄]^4‐—building units display isolated distorted tetrahedra.     

Mixed‐Valent Europium in the Cubic Thiosilicate Li3Eu6[SiS4]4

In an attempt to synthesize LiEu₃S₃[SiS₄] utilizing elemental europium and sulfur as well as SiS₂ and an excess of LiCl as flux and lithium source, dark red, platelet‐shaped single crystals of Li₃Eu₆[SiS₄]₄ were obtained. This new compound crystallizes in the cubic space group I4 3d (a = 1369.22(5) pm) with four formula units per unit cell. Both the Li⁺ and the Si⁴⁺ cations are surrounded by four sulfide anions. The [SiS₄]^4– tetrahedra show merely a slight trigonal distortion, while the [LiS₄]^7– units are best described as flattened bisphenoids. The europium cations exhibit an eightfold, rather irregular coordination environment by eight S^2– anions and have to be regarded mixed‐valent with a +2:+3 charge‐ratio of 5:1 in order to gain electroneutrality. The lack of an inversion center is caused by the [SiS₄]^4– tetrahedra being stacked exclusively top up along [111] in this acentric crystal structure.     

Thiosilicate der Selten‐Erd‐Elemente: I. Die isotypen Verbindungen KCe[SiS4] und Eu2[SiS4]

Thiosili‐Thiosilicates of the Rare‐Earth Elements: I. The Isotypic Compounds KCe[SiS₄] and Eu₂[SiS₄] Both isotypic thiosilicates KCe[SiS₄] (a = 649.15(6), b = 656.18(6), c = 863.96(8) pm, β = 107.531(9)°) and Eu₂[SiS₄] (a = 651.71(6), b = 659.54(6), c = 821.93(8) pm, β = 108.437(9)°) crystallize monoclinically in the space group P2₁/m and Z = 2. By the reaction of KCl, Ce₂S₃ and SiS₂ in the ratio 1 : 1 : 1 using a sixfold molar amount of KCl as flux in evacuated silica tubes (7 d, 850°C) brownish yellow, plate‐shaped single crystals, resistant both to air and water are obtained. The conversion of Eu, S and SiS₂ in molar ratios of 2 : 2 : 1 with an excess of CsCl as flux in evacuated silica tubes (7 d, 850°C) leads to deep red, plate‐shaped single crystals, which remain air‐ and water‐stable for a few days. The crystal structure contains isolated ortho‐thiosilicate units, that together with the Ce³⁺ or (Eu2)²⁺ cations build corrugated anionic layers parallel (001) according to {(Ce[SiS₄])^—} and {(Eu2[SiS₄])^2—}, respectively. These layers are alternatingly piled with cationic layers consisting solely of K⁺ or (Eu1)²⁺ cations. The latter show coordination numbers of eight in the shape of a bicapped trigonal prism, whereas the cations of the position Ce³⁺ and (Eu2)²⁺ have a (2+1)‐fold capped trigonal prismatic environment with a coordination number of 8+1. The comparison of both compounds KCe[SiS₄] and Eu₂[SiS₄] (≡ EuEu[SiS₄]) demonstrates, that Eu²⁺ is able to substitute both K⁺ and Ce³⁺ isomorphically.     

Kristallstruktur und magnetische Eigenschaften eines neuen Thiosilicats des Terbiums: Tb4[SiS4]3

Crystal Structure and Magnetic Properties of a New Thiosilicate of Terbium: Tb₄[SiS₄]₃ Terbium thiosilicate Tb₄[SiS₄]₃ was obtained by reaction of the elements in a bromine atmosphere in silica ampoules. The crystal structure was determined by single crystal X—ray diffraction methods (monoclinic, P2₁/n, Z = 4, a = 983.6(2) pm, b = 1096.4(2) pm, c = 1639.1(3) pm, b = 102.76(2)°). The structure is characterized by four crystallographically independent terbium positions with coordination numbers seven and eight as well as isolated [SiS₄]^4—‐tetrahedra. The magnetic behaviour of powdered crystals was interpreted by theoretical calculations where the influence of the crystal field was taken into account by applying the angular overlap model and magnetic exchange by the molecular field approximation.     

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—.