Kalium-Doppelsalze mit den gemischten Trisulfidometallat-Ionen [MoOS3]2- und [WOS3]2- / Potassium Double Salts with the Mixed Trisulfidometalate Ions [MoOS3]2- and [WOS3]2-

2013 ◽  
Vol 68 (7) ◽  
pp. 761-777 ◽  
Author(s):  
Anna J. Lehner ◽  
Caroline Röhr
Keyword(s):  
Structure Type ◽  
Double Salt ◽  
Crystallographic Group ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
X Ray ◽  
Double Salts ◽  
Mixed Salts ◽  
Type Orthorhombic ◽  
Derivatives Of

In the course of the synthesis of mixed oxidosulfido molybdates and tungstates by passing H2S gas through solutions of the oxido metalates, several new salts containing the metalates [MOS3]2- besides further anions (halides X-, hydrosulfide SH- or thiosulfate S2O2-3) were obtained as well-formed crystals. Their crystal structures have been determined using single crystal X-ray data. The salts containing SH- as the additional anion crystallize with a new structure type (orthorhombic, space group Pmn21, M=Mo=W, TM =20=-125 °C: a=957.7(2)/954.15(2), b=636.2(2)/636.19(1), c=812.4(2)/809.88(2) pm, Z =2, R1=0.0319=0.0185). The mixed sulfidomolybdate/ chloride K3[MoO1.25S2.75]Cl (orthorhombic, space group Pca21, a=1246.3(1), b=623.20(4), c=1230.44(8) pm, Z =4, R1=0.0472) is isotypic with the sulfidotungstate K3[WOS3]Cl, but contains 25% of the disulfido molybdate. The structures of the SH- and the Cl- salts are closely related: In both cases, the trisulfido metalates are overall coordinated by cuboctahedra of 12 K+ ions, and the small additional anions are centered in K+ octahedra. In this regard, the structures are both derivatives of the cubic perovskite (and thus the Cu3Au) type. This crystallographic group-subgroup relation is discussed in detail. Yellow hexagonal columns of the double salt K6[WOS3]2(S2O3) were obtained by the methanothermal decomposition of the disulfidotungstate K2[WO2S2]. It crystallizes with a new structure type (hexagonal, space group P63mc, a=983.78(8), c=1227.3(1) pm, Z =2, R1=0.0175). Like in the other mixed salts, the two crystallographically different [WOS3]2- anions exhibit an overall cuboctahedral coordination by 12 potassium cations. The smaller S2O2-3 anions are surrounded by nine K+ ions arranged in the form of two flat facesharing octahedra. Again similar to the mixed halides and hydrosulfides, the two K polyhedra around the anions, here present in a 2 : 1 ratio, are arranged in a space-filling packing, in this case related to the ht- BaMnO3 (and thus the Ni3Ti) structure type. According to their ‘double salt’ character, the Mo/W-O and Mo/W-S distances and the intramolecular vibrational frequencies of the tetrahedral moieties of the title compounds are similar between them and those in the pure potassium trisulfido metalates. This further becomes apparent from the additive nature of their molar volumes, which correspond to the sum of the volumes of the simple salts KCl, KSH or K2(S2O3) and K2[MoOS3].

Gemischte Alkalimetall-Oxidosulfidomolybdate A2[MoOxS4– x] (x = 1, 2, 3; A = K, Rb, Cs, NH4). Synthesen, Kristallstrukturen und Eigenschaften / Mixed Alkali Oxidosulfidomolybdates A2[MoOxS4−x] (x = 1, 2, 3; A = K, Rb, Cs, NH4).Synthesis, Crystal Structure and Properties

2012 ◽  
Vol 67 (2) ◽  
pp. 127-22
Author(s):  
Anna J. Lehner ◽  
Korina Kraut ◽  
Caroline Röhr
Keyword(s):  
Bathochromic Shift ◽  
Structure Type ◽  
Structure Theory ◽  
Monoclinic Space Group ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
Coordination Numbers ◽  
Preparation Conditions ◽  
Vis Spectroscopy ◽  
Type Orthorhombic

Mixed sulfido/oxidomolybdate anions [MoOxS4−x]2− (x = 1, 2, 3) have been prepared by passing H2S gas through a solution of oxidomolybdates. The alkali salts of K+, Rb+, Cs+, and NH+4 precipitate as crystalline salts from these solutions depending on the pH, the polarity of the solvent, the educt concentrations and the temperature. Their structures have been determined by means of X-ray single-crystal diffraction data. All trisulfidomolybdates A2[MoOS3] (A = NH4/K/Rb/Cs) are isotypic with the tetrasulfido salts, exhibiting the β -K2[SO4] type (orthorhombic, space group Pnma, Z = 4; for A = Rb: a = 940.62(4), b = 713.32(4), c = 1164.56(5) pm, R1 = 0.0281). In contrast, the disulfidomolybdates exhibit a rich crystal chemistry, forming three different structure types depending on the preparation conditions and the size of the A cation: All four cations form salts crystallizing with the (NH4)2[WO2S2] structure type (monoclinic, space group C2/c, Z = 4, for A = Rb: a = 1144.32(11), b = 732.60(4), c = 978.99(10) pm, β = 120.324(7)°, R1 = 0.0274). For the three alkali metal cations a second polymorph with a new structure type (monoclinic, space group P21/c, Z = 4) is observed in addition (for A = Rb: a = 674.83(2), b = 852.98(3), c = 1383.10(9) pm, β = 115.19(1)°, R1 = 0.0216). The cesium salt also crystallizes with a third modification of another new structure type (orthorhombic, space group Pbcn, Z = 4, a = 915.30(6), b = 777.27(7), c = 1120.02(7) pm, R1 = 0.0350). Only for K, an anhydrous monosulfidomolybdate could be obtained (K2[MoO4] structure type, monoclinic, space group C2/m, Z = 4, a = 1288.7(3), b = 615.7(2), c = 762.2(1) pm, β = 109.59(1)°, R1 = 0.0736). The intramolecular chemical bonding in the molybdate anions is discussed and compared with the respective vanadates. Hereby aspects like bond lengths, bond strengths and force constants derived from Raman spectroscopy, are taken into account. Especially for the polymorphic disulfido salts, in-depth analyses of the local coordination numbers and the packing of the ions are presented. The gradual bathochromic shift of the crystal color with increasing S content and increasing size of the counter cations A and molar volumes (for the polymorphic forms), respectively, is in accordance with the increase of the experimental (UV/Vis spectroscopy) and calculated (FP-LAPW band structure theory) band gaps.

A new ternary silicide GdFe1−xSi2 (x=0.32): preparation, crystal and electronic structure

2020 ◽  
Vol 75 (1-2) ◽  
pp. 217-223
Author(s):  
Volodymyr Babizhetskyy ◽  
Jürgen Köhler ◽  
Yuriy Tyvanchuk ◽  
Chong Zheng
Keyword(s):  
Electronic Structure ◽  
Tight Binding ◽  
Structure Type ◽  
X Ray Diffraction ◽  
Orthorhombic Space Group ◽  
X Ray ◽  
Arc Melting ◽  
Lmto Method ◽  
Type Orthorhombic ◽  
Crystal And Electronic Structure

AbstractThe title compound was prepared from the elements by arc-melting. The crystal structure was investigated by means of single-crystal X-ray diffraction. It crystallizes in the TbFeSi2 structure type, orthorhombic space group Cmmm, a = 4.0496(8), b = 16.416(2), c = 3.9527(6) Å, Z = 4, R1 = 0.041, wR2 = 0.11 for 207 unique reflections with Io > 2 σ(Io) and 19 refined parameters. The Fe position is not fully occupied and the refinement results in a composition GdFe0.68Si2 in agreement with a chemical analysis. The structure consists of zig-zag chains of Si(1) atoms which are terminally bound to additional Si(2) atoms. For an ordered variant GdFe0.5Si2 the Zintl concept can be applied which results in formal oxidation states Gd3+(Fe2+)0.5Si(1)1−Si(2)3−. The electronic structure of this variant GdFe0.5Si2 was analyzed using the tight-binding LMTO method and the results confirm the simple bonding picture.

CaAgxZn1– x: Zwischen CrB- und FeB-Strukturtyp – Eine Studie zu elektronischen Einflüssen auf die Stapelung von Zick-Zack-Ketten in polaren Erdalkalimetall-Monometalliden / CaAgxZn1−x: Between CrB and FeB Structure Type – A Study on Electronic Factors Influencing the Stacking of Zig-zag Chains in Polar Alkaline Earth Monometallides

2009 ◽  
Vol 64 (10) ◽  
pp. 1127-1142 ◽  
Author(s):  
Wiebke Harms ◽  
Viktoria Mihajlov ◽  
Marco Wendorff ◽  
Caroline Röhr
Keyword(s):  
Alkaline Earth ◽  
Valence Electron ◽  
Computational Study ◽  
Structure Type ◽  
Binary Compound ◽  
Monoclinic Space Group ◽  
Stacking Sequence ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
Type Orthorhombic

Depending on both electronic (valence electron numbers) and geometric (atom size ratios) characteristics of the contributing elements, the 1 : 1 compounds AIIM of the heavier alkaline earth elements A and electron-rich transition metals M form the well known CrB or FeB structure types. Both structure types exhibit M zig-zag chains, which are stacked in different orientations. In systematic studies of the pseudo-binary section CaAgxZn1−x four new ternary phases with different stacking variants between the CrB (cubic stacking, c) and the FeB (hexagonal stacking, h2) structure type have been prepared and characterized on the basis of single crystal X-ray data. Starting from CaAg (CrB type, orthorhombic, space group Cmcm, a = 405.22(7), b = 1144.7(2), c = 464.43(11) pm, Z = 4, R1 = 0.0197), up to 24% of Ag (CaAg0.76Zn0.24: a = 408.6(2), b = 1144.3(5), c = 460.7(2) pm, R1 = 0.0208) can be substituted by zinc without a change in the structure type. Close to the 1 : 1 ratio of Ag and Zn, the HT-TbNi structure type with the stacking sequence (hc2)2, i. e. 33% hexagonality (CaAg0.52Zn0.48: orthorhombic, space group Pnma, a = 2345.47(6), b = 454.370(10), c = 609.950(10) pm, Z = 12, R1 = 0.0298) is formed, followed by the SrAg type with 50% hexagonality (CaAg0.48Zn0.52: orthorhombic, space group Pnma, a = 1571.0(2), b = 451.50(7), c = 609.80(9) pm, Z = 8, R1 = 0.0733). The amount of hexagonal stacking is further increased with increasing Zn content in CaAg0.33Zn0.67 (Gd0.7Y0.3 structure type, h2c stacking, 67% hexagonality, monoclinic, space group P21/m, a = 610.39(9), b = 448.53(5), c = 1195.7(2) pm, β = 96.829(14)◦, Z = 3, R1 = 0.0221). Finally, a pure hexagonal stacking sequence, i. e. the FeB structure type (orthorhombic, space group Pnma, Z = 4) is observed from CaAg0.14Zn0.86 (a = 804.57(2), b = 443.050(10), c = 611.350(10) pm, R1 = 0.0131) to CaAg0.06Zn0.94 (a = 806.1(3), b = 441.0(2), c = 610.4(3) pm, R1 = 0.0255). Intriguingly, the series ends with the binary compound CaZn, which again crystallizes with the CrB structure type exhibiting cubic stacking of the zig-zag chains only (0% hexagonality). In an accompanying computational study, the chemical bonding in the series Ca(Ge/Ga/Zn/Ag) of isotypic binary metallides with variable valence electron numbers has been analyzed using FP-LAPW band structure methods. The electronic structures of the two border stacking variants are compared using the crystal data of CaZn (CrB type) and CaAg0.06Zn0.94 (FeB type). Geometrical and electronic criteria are used to compare and discuss the stability ranges of the different stacking variants inbetween the CrB and the FeB structure type found in polar intermetallic 1 : 1 phases.

Crystal Structure of the New Compound NdFeSb3

2007 ◽  
Vol 353-358 ◽  
pp. 3043-3046 ◽  
Author(s):  
Ping Li Qin ◽  
Liang Qin Nong ◽  
Ji Liang Zhang ◽  
Hai Qing Qin ◽  
Jiang Ping Liao ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Powder Diffraction ◽  
Rietveld Method ◽  
Structure Type ◽  
Lattice Parameters ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
X Ray

The crystal structure of a new compound NdFeSb3 has been determined by X-ray powder diffraction using the Rietveld method. The compound crystallizes in the orthorhombic, space group Pbcm (No.57) with the CeNiSb3 structure type and lattice parameters a=1.26828(2)nm, b=0.61666(2)nm, c=1.81867(4) nm, z=12 and Dcalc=7.917g/cm3.

Ba5(Al/Ga)5(Sn/Pb): Neue Verbindungen an der Zintl-Grenze / Ba5(Al/Ga)5(Sn/Pb): New Compounds at the Zintl Border

2006 ◽  
Vol 61 (7) ◽  
pp. 846-853 ◽  
Author(s):  
Kristin Guttsche ◽  
Angela Rosin ◽  
Marco Wendorff ◽  
Caroline Röhr
Keyword(s):  
Structure Type ◽  
Intermetallic Phases ◽  
Zintl Phases ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
Ternary Compounds ◽  
Maximum Temperatures ◽  
New Compounds ◽  
Type Orthorhombic ◽  
Structural Aspects

The new isotypic intermetallic phases Ba5MIII5MIV (MIII = Al, Ga; MIV = Sn, Pb) have been synthesized from stoichiometric amounts of the elements at maximum temperatures of 900 to 1000 ◦C. They crystallize in the hexagonal space group P6̄m2 (Ba5Al5Sn: a = 605.05(8), c = 1109.0(2) pm, R1 = 0.0137; Ba5Ga5Sn: a = 599.45(5), c = 1086.00(7) pm, R1 = 0.0485; Ba5Al5Pb: a = 606.9(2), c = 1112.0(4) pm, R1 = 0.0409 and Ba5Ga5Pb: a = 601.76(7), c = 1091.51(13) pm, R1 = 0.0295), forming a new structure type. Similar to the Zintl phases Ba2MIV (Co2Si structure type, orthorhombic, space group Pnma; Ba2Sn: a = 861.52(14), b = 569.85(9), c = 1056.9(2) pm, R1 = 0.0217 and Ba2Pb: a = 865.12(13), b = 569.1(2), c = 1061.8(2) pm, R1 = 0.0470), these new ternary phases contain isolated MIV atoms (coordinated by 11 Ba atoms). In addition, sheets of 3- and 4-bonded Al/Ga atoms similar to those in Ba3Al5 are present. In accordance with this, a formal subdivision of Ba5MIII5MIV into Ba3MIII5 ・ Ba2MIV can be performed to describe the observed intergrowth or chemical twinning of two different binary intermetallics to give the new ternary compounds. Beyond structural aspects, also the nature of the chemical bonding (as studied by FP-LAPW calculations) in these new, non-electron precise compounds in the vicinity of the Zintl border can be interpreted in this vein.

Cadmium-Auride AIICdxAu2– x (AII = Ca, Sr) Synthese, Kristallstruktur, chemische Bindung/ Cadmium-Aurides AIICdxAu2−x (AII = Ca, Sr) – Synthesis, Crystal Structure, Chemical Bonding

2009 ◽  
Vol 64 (5) ◽  
pp. 471-486 ◽  
Author(s):  
Wiebke Harms ◽  
Ines Dürr ◽  
Caroline Röhr
Keyword(s):  
Elevated Temperatures ◽  
Structure Type ◽  
Ambient Conditions ◽  
Orthorhombic Space Group ◽  
Continuous Transition ◽  
Space Group ◽  
The Difference ◽  
Simple Phase ◽  
Type Orthorhombic ◽  
Phase Width

Following the observation that the binary dicadmides and diaurides of calcium and strontium (A) both form the KHg2 structure type, the two sections AIICdxAu2−x have been studied systematically by means of synthetic, X-ray structural and theoretical investigations. The binary border compound CaCd2 is dimorphic forming the KHg2 structure at elevated temperatures (orthorhombic, space group Imma, a = 488.63(9), b = 754.1(2), c = 851.3(2) pm, Z = 4, R1 = 0.0498) and the MgZn2-type Laves phase at ambient conditions (hexagonal, space group P63/mmc, a = 599.71(9), c = 962.7(2) pm, Z = 4, R1 = 0.0309). Starting from the known binary calcium auride CaAu2 only a very small amount of Au can be replaced by Cd. Around the 1 : 1 ratio of Au and Cd the TiNiSi structure type (orthorhombic, space group Pnma), an ordered variant of the KHg2 type, has a small homogeneity range (CaCdxAu2−x with x = 1/0.76(2): a = 735.0(1)/731.7(1), b = 433.66(6)/431.43(7), c = 873.7(2)/869.9(2) pm, Z = 4, R1 = 0.0482/0.0539). The analogous structure type is also observed in the Sr compounds with the difference that in this case a continuous transition from the KHg2 type of SrAu2 (i. e. x = 0) towards the distorted TiNiSi structure type (up to x = 0.86) is observed in the series SrCdxAu2−x (for x = 0.86(1)/0.45(1): a = 764.0(1)/758.4(1), b = 458.07(7)/474.6(1), c = 872.16(12)/829.2(2) pm, Z = 4, R1 = 0.0446/0.0410). Attempts to prepare the Ca compounds of intermediate composition around a Cd content of x ≈ 0.5 resulted in the formation of the Aurich phase Ca5Cd2Au10 crystallizing with the Zr7Ni10 structure type (orthorhombic, space group Cmca, a = 1390.6(4), b = 1015.7(3), c = 1025.6(2) pm, Z = 4, R1 = 0.0657). In this compound, Cd and Ca occupy common crystallographic sites, which are occupied by In in the isotypic ternary compound Ca4In3Au10. Similarly, at the Cd-rich parts of the sections AIICdxAu2−x no simple phase width of the KHg2 structure type exists. In the case of the calcium series the new compound Ca11Cd18Au4, which shows only a very small phase width, is formed instead. This compound crystallizes with a new structure type (Ca11Cd18+xAu4−x with x = 0.6/0: tetragonal, space group I41/amd, a = 1030.83(6)/1029.39(6), c = 3062.5(3)/3051.0(3) pm, Z = 4, R1 = 0.0475/0.0379) exhibiting a complicated Cd/Au polyanion with four-, five- and six-bonded Cd/Au atoms. The results of FPLAPWband structure calculations are used to explain the electronic stability of the compounds. The calculated Bader charges of cadmium and gold atoms (and In and Au atoms for comparison) are used to discuss the transition between Cd-rich cadmides (like CaCd2 and Ca11Cd18Au4), auridocadmates (like CaCdAu) and the Cd-poor cadmium aurides (like Ca5Cd2Au10).

Aluminium-Germanide der zweiwertigen Lanthanoide Eu und Yb: Synthese, Strukturchemie und chemische Bindung

2011 ◽  
Vol 66 (8) ◽  
pp. 793-812
Author(s):  
Britta Bauer ◽  
Caroline Röhr
Keyword(s):  
Alkaline Earth ◽  
Building Blocks ◽  
Structure Type ◽  
Monoclinic Space Group ◽  
Total Density ◽  
Structural Element ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
Type Orthorhombic ◽  
Total Density Of States

In the course of attempts to substitute Ca by Yb and Sr by Eu in known alkaline earth Al-germanides, the four new ternary compounds Eu3Al1.8Ge2.2, Eu3 Al2Ge4, Yb2 AlGe3, and Yb17Al8Ge19 have been synthesized from mixtures of the elements and their crystal structures determined by means of single-crystal X-ray data. The two europium compounds Eu3Al1.8Ge2.2 (Ta3B4 structure type, orthorhombic, space group Immm, a = 417.68(3), b = 470.70(3), c = 1897.2(2) pm, Z = 2, R1 = 0.0439) and Eu3Al2Ge4 (Sr3Al2Ge4 structure type, monoclinic, space group C2/m, a = 1235.9(6), b = 416.8(2), c = 878.4(4) pm, β = 110.615(13)°, Z = 2, R1 = 0.0978) are isotypic with the corresponding strontium phases. After ionic decomposition, the layers [Al2- Ge4- ]6− in Eu3Al2Ge4 with four-bonded Al and three-bonded Ge atoms can be interpreted as electron-precise Zintl anions. In contrast, the planar ribbons 1∞[Al2/2Ge2Al2/2] of condensed six-membered rings in Eu3Al1.8Ge2.2 exhibit considerably shorter Al-Ge bonds and an Al-Al bond length of only 251 pm. Yb2AlGe3 (orthorhombic, space group Pnma, a = 682.20(10), b = 417.87(9), c = 1813.9(3) pm, Z = 4, R1 = 0.0415) crystallizes with the Y2AlGe3 structure type. Folded [Al2Ge2] ladders, also found in Eu3Al2Ge4 and the known compound Yb7Al5Ge8, are connected by planar cis/trans chains of Ge atoms. The total density of states calculated within the FP-LAPW|DFT band structure approach shows a distinct minimum at the Fermi level for the electron precise Zintl compound Eu3Al2Ge4, whereas π-bonding contributions are evident from the band structures of Eu3Al2Ge2 and Yb2AlGe3. In full accordance, the tDOS of both compounds exhibits no minimum at EF, small phase widths are possible for Eu3Al2Ge2 and related alkaline earth compounds, and Yb2AlGe3 is isotypic with several other more electron-rich LnIII compounds. The complicated structure of the new compound Yb17Al8Ge19 (tetragonal, space group P4/nmm, a = 1542.50(2), c = 788.285(8) pm, Z = 2, R1 = 0.0282) contains three different building blocks: distorted [Al4Ge4] heterocubane units are interconnected by four-bonded Ge atoms to form columns running along the c axis. Secondly, eight-membered rings are formed by alternating Al and Ge atoms, each being in a trigonal-planar Al/Ge coordination. The rings are terminated by Ge atoms (bonded to Ge of the ring) and linked to the first structural unit by a further Ge atom (bonded to Al of the ring). Thirdly, inside the large channels, which are formed by the packing of the eightmembered rings, Ge2 dumbbells are interspersed as a third structural element.

Neue gemischte Sr/Ba-Trielide AIIInxMIII1– x (M = Ga, Al)

2008 ◽  
Vol 63 (7) ◽  
pp. 804-818 ◽  
Author(s):  
Marco Wendorff ◽  
Caroline Röhr
Keyword(s):  
Ternary System ◽  
Single Crystal ◽  
Composition Range ◽  
Structure Type ◽  
Orthorhombic Space Group ◽  
Triclinic Space Group ◽  
Space Group ◽  
X Ray ◽  
New Compounds

A series of new ternary mixed Sr and Ba trielides of overall composition 1 : 1 was synthesized from stoichiometric quantities of the elements. The structures of the new compounds were determined using single crystal X-ray data. In the case of the Sr compounds, commensurately modulated new superstructures of the CrB type are formed in the In-rich part of the ternary system SrAl - SrGa - SrIn: The gallides, SrIn1−xGax (x = 0.30, orthorhombic, space group Ima2, a = 1954.2(7), b = 1305.6(4), c = 1272.6(3) pm, Z = 48, R1 = 0.0848) are formed in the composition range x = 0.20 to 0.30. The closely related aluminide SrIn1−xAlx (x = 0.04, orthorhombic, space group Pnna, a = 1280.1(7), b = 1482.0(5), c = 1308.7(5) pm, Z = 36, R1 = 0.1164) and the isotypic Zn compound SrIn0.90Zn0.10 (a = 1277.7(4), b = 1489.9(3), c = 1301.3(4) pm, R1 = 0.0629) also contain mainly In as the triele element. The structures, similar to CrB, contain zig-zag chains of two-bonded In-Ga/Al, in which the ordering of the trieles results in a strong wavelike form of the originally planar zig-zag chains. In contrast, no corresponding Ba compounds were formed. Instead, BaIn0.46Ga0.54 (triclinic, space group P1̄, a = 661.1(3), b = 679.4(2), c = 712.4(3) pm, α = 69.13(3), β = 77.14(3), γ = 84.27(3)°, Z = 2, R1 = 0.0557) crystallizes with a new structure type and exhibits a planar rhomb-like anion with both two- and three-bonded In/Ga atoms. Attempts to obtain 1 : 1 compounds in-between BaAl and BaIn resulted in the formation of the 5 : 6 phases Ba5In6−xAlx (x = 4.1/5.1, hexagonal, space group P6̄m2, a = 612.2(4)/608.6(1), c = 1124.6(10)/1116.80(6) pm, Z = 1, R1 = 0.0608/0.0147) which are isotypic to Ba5M5IIIMIV (MIII = Al, Ge; MIV = Sn, Pb). Their structures contain isolated In anions (coordinated by 11 Ba atoms) and sheets of 3- and 4-bonded Al/In atoms similar to those known from the structures of Ba aluminides like Ba3Al5.

Neue Lanthan-Stannide/Germanide: La3Sn4.4Ge0.6, La3Sn3.1Ge0.9 und La9Sn6.7Ge3.3 / New Lanthanum Stannide/Germanides: La3Sn4.4Ge0.6, La3Sn3.1Ge0.9 and La9Sn6.7Ge3.3

2011 ◽  
Vol 66 (10) ◽  
pp. 1015-14
Author(s):  
Ines Dürr ◽  
Caroline Röhr
Keyword(s):  
Electronic Structure ◽  
Building Blocks ◽  
Structure Type ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
X Ray ◽  
Electron Counting ◽  
Square Planar ◽  
Counting Rules ◽  
Zintl Ions

Three new ternary mixed lanthanum stannide/germanides have been synthesized and characterized in the course of a systematic study of the phase formation at the 3 : 5, 3 : 4 and 1 : 1 pseudo-binary sections of the ternary system La - Ge - Sn, i. e. a study of the ’coloring’ in mixed tetrelides. The structures of the title compounds have been determined using single-crystal X-ray data, and the electronic structure was analyzed by means of simple electron counting rules and FP-LAPW band structure methods. Even a very minor substitution of Sn by Ge in the 3 : 5 stannide La3Sn5 already changes the structure from the Pu3Pd5 type of the binary stannide towards the Tl4PbTe3 type (La3Sn4.4Ge0.6: tetragonal, space group I4/mcm, a = 861.35(10), c = 1211.48(13) pm, Z = 4, R1 = 0.0420). According to the anionic building blocks present, isolated [Ge/Sn]4− anions and heavily puckered 4.82 nets of three-bonded tin atoms (i. e. [Sn4]4− Zintl ions), a small formal electron excess (+9/−8) occurs, which is also apparent from the position of the minimum in the calculated tDOS. In contrast, starting from the known binary stannide La3Sn4 (orthorhombic, space group Cmcm, Er3Ge4 structure type) a substitution of tin by germanium is possible without a change of the structure type up to the border composition La3Sn3.1Ge0.9 (a = 448.61(5), b = 1170.68(14), c = 1556.0(2) pm, Z = 4, R1 = 0.0380). Germanium preferentially occupies the sites of the [Ge/Sn]3 trimers, whereas the site of the square-planar coordinated Sn(3), which is stabilized by hypervalent bonding, is not populated by germanium. Taking the respective partial bonding into account, the Zintl electron count is also nearly exact (+9/−8). The new complex mixed tetrelide La9Sn6.7Ge3.3 (tetragonal, space group P42/ncm, a = 1602.04(3), c = 1724.42(5) pm, Z = 8, R1 = 0.0706) exhibits nine crystallographically different tetrel positions, which are occupied by isolated Sn and Ge atoms, [Sn/Ge]2 dumbbells, bent [Sn3] trimers, planar four-membered rings [Ge4], and planar six-membered rings [M6]. In this compound, the electron count following the Zintl concept also reveals only a very small formal excess of electrons (+54/−52).

Lanthan-Triel/Tetrel-ide La(Al,Ga)x(Si,Ge)1-x. Experimentelle und theoretische Studien zur Stabilität intermetallischer 1 : 1-Phasen / Lanthanum Triel/Tetrel-ides La(Al,Ga)x(Si,Ge)1−x. Experimental and Theoretical Studies on the Stability of Intermetallic 1:1 Phases

2011 ◽  
Vol 66 (11) ◽  
pp. 1107-15 ◽  
Author(s):  
Ines Dürr ◽  
Britta Bauer ◽  
Caroline Röhr
Keyword(s):  
Structure Type ◽  
Structural Elements ◽  
Orthorhombic Space Group ◽  
Stability Range ◽  
Space Group ◽  
The Stability ◽  
Type Orthorhombic ◽  
Experimental And Theoretical Studies ◽  
Stability Ranges ◽  
Phase Width

Systematic studies of the phase formation at the binary sections LaSi - LaGa and LaGe - LaAl have been carried out by means of synthetic, crystallographic and bond theoretical methods. The hightemperature forms of the two binary monotetrelides LaSi and LaGe crystallize with the FeB structure type, whereas LaGa forms the related CrB type and LaAl the significantly different CeAl type. Starting from LaSi/LaGe, the FeB type (orthorhombic, space group Pnma, Z = 4, a = 839.2(1)/842.7(1), b = 399.9(1)/412.3(1), c = 606.2(2)/612.2(1) pm, R1 = 0.0356/0.0298) remains stable only down to a valence electron number per M atom (M = Si, Ge, Al, Ga) of 6.9 (LaGa0.10Si0.90: a = 840.14(7), b = 404.12(12), c = 608.5(2) pm, R1 = 0.0513; LaAl0.15Ge0.85: a = 845.40(7), b = 414.08(13), c = 614.08(14) pm, R1 = 0.0213). In the system LaGaxSi1−x, the stability range of the CrB type (orthorhombic, space group Cmcm, Z = 4) starts at a gallium proportion of 25% (LaGa0.25Si0.75: a = 450.03(8), b = 1140.5(2), c = 406.05(6) pm, R1 = 0.0163) and extends to the border compound LaGa (v. e./M = 6). The CrB type also occurs in the system La-Al-Ge, but is in this case only formed around the 1 : 1 composition in between LaAl0.42Ge0.58 (a = 455.90(12), b = 1161.1(3), c = 418.05(9) pm, R1 = 0.0474) and LaAl0.61Ge0.39 (a = 454.89(10), b = 1168.8(2), c = 420.41(11) pm, R1 = 0.0447). These stability ranges, the variations of several key geometric parameters such as the M-M distances or the heights of the trigonal prisms, and the main aspects of the chemical bonding in these lanthanum monometallides are analyzed using FP-LAPWband structure methods. The structure of the new compound La2Al2Ge (V2B3 structure type, orthorhombic, space group Cmcm, a = 416.69(4), b = 2719.7(4), c = 450.46(5) pm, Z = 2, R1 = 0.0458) combines the structural elements of the CrB/FeB structure family (two-bonded M atoms) with the trigonally planar bonded M atoms of the ThSi2 type in a fully ordered Al and Ge atom distribution and thus without phase width

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