Preparation and Crystal Structures of Ternary Rare Earth Osmium Gallides LnOsGa3 (Ln = Gd—Tm) and LnOsGa3 (Ln = La—Nd)

The title compounds were prepared from the elemental components at high temperatures. The compounds LnOsGa₃ crystallize with the cubic TmRuGa₃ type structure which was refined from four‐circle X‐ray diffractometer data of TbOsGa₃: Pm3¯m, Z = 3, a = 640.8(1) pm, R = 0.014 for 173 structure factors and 10 variable parameters. The other gallides crystallize with a new structure type which was determined from single‐crystal X‐ray data of CeOsGa₄: Pmma, Z = 6, a = 963.9(2) pm, b = 880.1(1) pm, c = 767.0(1) pm, R = 0.030 for 744 F values and 56 variables. The structure may be considered as consisting of two kinds of alternating layers, although bonding within and between the layers is of similar strength. One kind of layers (A) is slightly puckered, two‐dimensionally infinite, hexagonal close packed, with the composition OsGa₃; the other kind of layers (B) is planar with the composition CeGa. The structure is closely related to that of Y₂Co₃Ga₉ where the corresponding layers have the compositions Co₃Ga₆ (A) and Y₂Ga₃ (B).     

Preparation and Crystal Structure of the Ternary Lanthanoid Platinum Antimonides Ln3Pt7Sb4 (Ln = Ce,Pr, Nd,and Sm) with Er3Pd7P4 Type Structure

The four compounds Ln₃Pt₇Sb₄ (Ln = Ce, Pr, Nd, and Sm) 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 from four‐circle X‐ray diffractometer data of Nd₃Pt₇Sb₄ [C2/m, a = 1644.0(2) pm, b = 429.3(1) pm, c = 1030.6(1) pm, β = 128.58(1)°, Z = 2, R = 0.032 for 698 structure factors and 46 variable parameters] and Sm₃Pt₇Sb₄ [a = 1639.5(2) pm, b = 427.1(1) pm, c = 1031.8(1) pm, β = 128.76(1)°, Z = 2, R = 0.025 for 816 F‐values and 46 variables]. The structure is isotypic with that of the homologous phosphide Er₃Pd₇P₄. In contrast to the structure of this phosphide, where the phosphorus atoms have the coordination number nine, the larger antimony atoms of Nd₃Pt₇Sb₄ obtain the coordination number ten. The structural relationships between the structures of EuNi_2—xSb₂, EuPd₂Sb₂, CeNi_2+xSb_2—x, Ce₃Pd₆Sb₅, and Nd₃Pt₇Sb₄, all closely related to the tetragonal BaAl₄ (ThCr₂Si₂) type structure, are briefly discussed emphasizing their space group relationships.     

Completing the Series: New Coordination Networks of Composition 3∞[RE2(ADC)3(H2O)6]·2H2O with RE = Pr,Nd, Sm,Eu, Tb,Dy, Ho,Er, Y and ADC2– = Acetylenedicarboxylate (–O2C–C≡C–CO2–)

The crystal structures of ³_∞[RE₂(ADC)₃(H₂O)₆] · 2H₂O (RE = Pr, Nd, Sm, Eu, Tb, Dy) were solved and refined from X‐ray single crystal data. They crystallize in a structure type already known for RE = La, Ce and Gd (P1 , no. 2, Z = 2), which is characterized by REO₉ polyhedra forming dimeric units being the nodes of a 3D framework structure linked by ADC^2– anions (^–O₂C–C≡C–CO₂^– = acetylenedicarboxylate). From synchrotron powder diffraction data it was shown that isostructural coordination networks are formed for RE = Ho, Er, Y, whereas for RE = Tm, Yb, Lu a new structure type crystallizing in a highly complex crystal structure with a large orthorhombic unit cell is found. All compounds are obtained by slow evaporation of an aqueous solution containing RE(OAc)₃ · xH₂O and acetylenedicarboxylic acid (H₂ADC). The coordination networks of composition ³_∞[RE₂(ADC)₃(H₂O)₆] · 2H₂O were thoroughly investigated by thermal analysis and for RE = Eu, Tb, a strong red and green photoluminescence was observed and investigated by means of UV/Vis spectroscopy.     

New Ternary Boride Carbides RE10B9+xC10–x (RE = Gd,Tb; x ≈︁ 0.2): Infinite Boron Carbon Branched Chains

New ternary rare earth metal boride carbides with compositions close to RE₁₀B₉C₁₀ (RE = Gd, Tb) were prepared from the elements by melting around 1800 K followed by annealing in silica tubes at 1270 K for one month. The crystal structure of the terbium compound was solved by single‐crystal X‐ray diffraction. It crystallizes in a new structure type in the monoclinic space group P2₁/c, a = 7.937(1), b = 23.786(2), c = 11.172(1) Å, β = 133.74(1)°, Z = 4, R1 = 0.045 (wR2 = 0.11) for 5713 reflections with I_o > 2σ(I_o). In the structure BC₂ units and single carbon atoms are attached to a zigzag boron chain forming the unprecedented B₁₈C₁₈ branching unit with a B–B distance of 2.42(2) Å between these units. In addition isolated carbon atoms occupy the centres of elongated octahedra formed by rare earth metal atoms. Disorder in the terbium position together with anomalous displacement ellipsoids for carbon atoms except of those in the BC₂ fragments can be rationalized in terms of a slight deviation in stoichiometry, Tb₁₀B_9+xC_10–x (x ≈? 0.2). The terbium compound is ferromagnetic below T_C ≈? 45 K. Due to the presence of moderately narrow domain walls the magneto‐crystalline energy is small.     

Structure determination of KScS2, RbScS2 and KLnS2 (Ln = Nd,Sm, Tb,Dy, Ho,Er, Tm and Yb) and crystal–chemical discussion

The title structures of KScS₂ (potassium scandium sulfide), RbScS₂ (rubidium scandium sulfide) and KLnS₂ [Ln = Nd (potassium neodymium sufide), Sm (potassium samarium sulfide), Tb (potassium terbium sulfide), Dy (potassium dysprosium sulfide), Ho (potassium holmium sulfide), Er (potassium erbium sulfide), Tm (potassium thulium sulfide) and Yb (potassium ytterbium sulfide)] are either newly determined (KScS₂, RbScS₂ and KTbS₂) or redetermined. All of them belong to the α‐NaFeO₂ structure type in agreement with the ratio of the ionic radii r³⁺/r⁺. KScS₂, the member of this structural family with the smallest trivalent cation, is an extreme representative of these structures with rare earth trivalent cations. The title structures are compared with isostructural alkali rare earth sulfides in plots showing the dependence of several relevant parameters on the trivalent cation crystal radius; the parameters thus compared are c, a and c/a, the thicknesses of the S—S layers which contain the respective constituent cations, the sulfur fractional coordinates z(S²⁻) and the bond‐valence sums.     

Composition and Crystal Structure of SmSb2O4Cl Revisited – and the Analogy of Sm1.5Sb1.5O4Br

The quaternary halide‐containing samarium(III) oxidoantimonates(III) Sm_1.3Sb_1.7O₄Cl and Sm_1.5Sb_1.5O₄Br were synthesized through solid‐state reactions from the binary components (Sm₂O₃, Sb₂O₃ and SmX₃, X = Cl and Br) at 750 °C in evacuated fused silica ampoules. They crystallize tetragonally in the space group P4/mmm, like the basically isotypic bismuthate(III) compounds SmBi₂O₄Cl and SmBi₂O₄Br, but show larger molar volumes and therefore contradict an ideal composition of “SmSb₂O₄X” (X = Cl and Br). Both single‐crystal X‐ray diffraction and quantitative electron‐beam microprobe analysis revealed the actual compositions of the investigated antimony(III) compounds, which can be understood as heavily Sm³⁺‐doped derivatives of “SmSb₂O₄X” hosts at the Sb³⁺ site. (Sm1)³⁺ is coordinated eightfold by oxygen atoms in the shape of a cube. The mixed‐occupied (Sb/Sm2)³⁺ cation has four oxygen atoms and four halide anions as neighbors forming a square antiprism. The oxygen atoms and anions establish alternating layers parallel to the ab‐plane, which alternate when stacked along [001].     

Rebuttal of the Existence of Solid Rare Earth Bicarbonates and the Crystal Structure of Holmium Nitrate Pentahydrate

The synthesis routes of Gd(HCO₃)₃ · 5H₂O and Ho(HCO₃)₃ · 6H₂O, which are the only known bicarbonates of rare earth metals, were refuted and the published crystal structures were discussed. Because of the structural relationship of Ho(HCO₃)₃ · 6H₂O to rare earth nitrate hexahydrates, 1 the synthesis of holmium nitrate hydrate was considered and the crystal structure of Ho(NO₃)₃ · 5H₂O was solved by single crystal X‐ray diffraction measurements. Ho(NO₃)₃ · 5H₂O was determined to crystallize in the triclinic space group P1 (no. 2) with a = 6.5680(14) Å, b = 9.503(2) Å, c = 10.462(2) Å, α = 63.739(14)°, β = 94.042(2)° and γ = 76.000(16)°. The crystal structure consists of isolated [Ho(H₂O)₄(NO₃)₃] polyhedra and non‐coordinating water molecules. It is isotypic to other rare earth nitrate pentahydrates.     

Inverse Perovskites (Eu3O)E with E = Sn,In – Preparation,Crystal Structures and Physical Properties

The cubic inverse Perovskites (Eu₃O)In and (Eu₃O)Sn were prepared from the metals and Eu₂O₃ or SnO₂, respectively. For (Eu₃O)In the crystal structure analysis was performed on single crystal X‐ray diffraction data (space group , a = 512.79(3) pm, Z = 1, R_gt(F) = 0.022, wR(F²) = 0.044). The data indicated full occupancy on all sites and a fully ordered structure. According to magnetic susceptibility measurements and X‐ray absorption spectroscopic data at the Eu L_III edge both compounds contain europium in the 4f⁷ (Eu²⁺) electronic state. (Eu₃O)In orders ferromagnetically at 185(5) K, (Eu₃O)Sn shows antiferromagnetic order at 31.4(2) K. Both compounds behave as metallic conductors in electrical resistivity measurements. However, (Eu₃O)In may be classified a metal, while (Eu₃O)Sn is more likely a heavily doped degenerated semiconductor or semimetal according to the absolute values of the resistivity.     

Spektroskopische und strukturelle Charakterisierung von Tris(2, 6‐di‐t‐butyl‐phenolato)lanthanid(III) (Ln(OAr′)3; Ln = Pr,Nd) sowie parametrische Analyse des Kristallfeld‐Aufspaltungsmusters von Nd(OAr′)3

Electronic Structures of Highly Symmetrical Compounds of f Elements. 37 [1] Spectroscopic and Structural Characterization of Tris(2, 6‐di‐t‐butyl‐phenolato)lanthanide(III) (Ln(OAr′)₃; Ln = Pr, Nd), and Parametric Analysis of the Crystal Field Splitting Pattern of Nd(OAr′)₃ Pr(OAr′)₃ and Nd(OAr′)₃ crystallize (at approximately 150 K and 200 K, respectively) in the monoclinic space group P2₁ with four molecules in the unit cell. If one considers only the directly coordinating oxygen atoms, the effective crystal field is of C_3v symmetry. The signals in the optical spectra of Pr(OAr′)₃ are broad using either solutions or solids, even at ca. 80‐90 K, thus they are not suitable for interpretation purposes. Nd(OAr′)_3, however, exhibits sharp absorption bands at room and low temperatures, which are assigned in analogy to the previously identified absorption transitions of Nd[N(SiMe₃)₂]₃ based on optical polarization measurements. The thus derived crystal field splitting pattern is simulated by fitting the free parameters of a phenomenological Hamiltonian, achieving a reduced r.m.s. deviation of 26.4 cm^—1 for 64 assignments. The parameters used allow the estimation of the ligand field strength associated with the (OAr′)^— ligand, the insertion of this ligand into empirical nephelauxetic and relativistic nephelauxetic series, and the setup of experimentally‐based non‐relativistic and relativistic molecular orbital schemes in the f range.     

Cobalt Centered Trigonal RE6 Prisms and Mg4 Clusters as Basic Structural Units in RE4CoMg (RE = Y,La, Pr,Nd, Sm,Gd–Tm)

The new rare earth metal rich intermetallic compounds RE₄CoMg (RE = Y, La, Pr, Nd, Sm, Gd–Tm) were prepared via melting of the elements in sealed tantalum tubes in a water‐cooled sample chamber of a high‐frequency furnace. The compounds were investigated by X‐ray diffraction of powders and single crystals: Gd₄RhIn type, , a = 1428.38(9) pm, wR2 = 0.0638, 680 F² values, 20 variables for La₄CoMg, a = 1399.5(2) pm, wR2 = 0.0584, 589 F² values, 20 variables for Pr₄CoMg, a = 1390.2(3) pm, wR2 = 0.0513, 634 F² values, 20 variables for Nd_3.90CoMg_1.10, a = 1381.0(3) pm, wR2 = 0.0730, 618 F² values, 22 variables for Sm_3.92Co_0.93Mg_1.08, a = 1373.1(4) pm, wR2 = 0.0586, 611 F² values, 20 variables for Gd_3.92CoMg_1.08, a = 1362.1(3) pm, wR2 = 0.0576, 590 F² values, 20 variables for Tb_3.77CoMg_1.23, a = 1344.8(2) pm, wR2 = 0.0683, 511 F² values, 20 variables for Dy_3.27CoMg_1.73, and a = 1343.3(2) pm, wR2 = 0.0560, 542 F² values, 20 variables for Er_3.72CoMg_1.28. The cobalt atoms have trigonal prismatic rare earth coordination. Condensation of the CoRE₆ prisms leads to a three‐dimensional network which leaves larger voids that are filled by regular Mg₄ tetrahedra at a Mg–Mg distance of 316 pm in La₄CoMg. The magnesium atoms have twelve nearest neighbors (3 Mg + 9 RE) in icosahedral coordination. In the structures with Nd, Sm, Gd, Tb, Dy, and Er, the RE1 positions which are not involved in the trigonal prismatic network reveal some RE1/Mg mixing and the Sm_3.92Co_0.93Mg_1.08 structure shows small cobalt defects. Considering La₄CoMg as representative of all studied systems an analysis of the chemical bonding within density functional theory closely reproduces the crystal chemistry scheme and shows the role played by the valence states of the different constituents in the electronic band structure. Strong bonding interactions were observed between the lanthanum and cobalt atoms within the trigonal prismatic network.     

Rare‐Earth‐Rich Magnesium Compounds RE23Rh7Mg4 (RE = La,Ce, Pr,Nd, Sm,Gd) with Tetrahedral Mg4 Clusters

The rare earth‐rich compounds RE₂₃Rh₇Mg₄ (RE = La, Ce, Pr, Nd, Sm, Gd) were prepared by induction‐melting the elements in sealed tantalum tubes. The new compounds were characterized by X‐ray powder diffraction. They crystallize with the hexagonal Pr₂₃Ir₇Mg₄ type structure, space group P6₃mc. The structures of La₂₃Rh₇Mg₄ (a = 1019.1(1), c = 2303.7(4) pm, wR2 = 0.0827, 1979 F² values, 69 variables), Nd₂₃Rh₇Mg₄ (a = 995.4(2), c = 2242.3(5) pm, wR2 = 0.0592, 2555 F² values, 74 variables) and Gd₂₃Rh_6.86(5)Mg₄ (a = 980.5(2), c = 2205.9(5) pm, wR2 = 0.0390, 2083 F² values, 71 variables) were refined from single crystal X‐ray diffractometer data. The three crystallographically different rhodium atoms have trigonal prismatic rare earth coordination with short RE–Rh distances (283–300 pm in Nd₂₃Rh₇Mg₄). The prisms are condensed via common edges, leading to a rigid three‐dimensional network in which isolated Mg₄ tetrahedra (312–317 pm Mg–Mg in Nd₂₃Rh₇Mg₄) are embedded. Temperature dependent magnetic susceptibility data of Ce₂₃Rh₇Mg₄ indicate Curie‐Weiss behavior with an experimental magnetic moment of 2.52(1) μ_B/Ce atom, indicative for stable trivalent cerium. Antiferromagnetic ordering is evident at 2.9 K.     

Orthorhombic HP‐REOF (RE = Pr,Nd, Sm – Gd) – High‐Pressure Syntheses and Single‐Crystal Structures (RE = Nd,Sm, Eu)

High‐pressure modifications of the rare earth oxide fluorides REOF (RE = Pr, Nd, Sm – Gd) were successfully synthesized under conditions of 11 GPa and 1200 °C applying the multianvil high‐pressure/high‐temperature technique. Single crystals of HP‐REOF (RE = Nd, Sm, Eu) were obtained making it possible to analyze the products by means of single‐crystal X‐ray diffraction. The compounds HP‐REOF (RE = Nd, Sm, Eu) crystallize in the orthorhombic α‐PbCl₂‐type structure (space group Pnma, No. 62, Z = 4) with the parameters a = 632.45(3), b = 381.87(2), c = 699.21(3) pm, V = 0.16887(2) nm³, R₁ = 0.0156, and wR₂ = 0.0382 for HP‐NdOF, a = 624.38(3), b = 376.87(2), c = 689.53(4) pm, V = 0.16225(2) nm³, R₁ = 0.0141, and wR₂ = 0.0323 for HP‐SmOF, and a = 620.02(4), b = 374.24(3), c = 686.82(5) pm, V = 0.15937(2) nm³, R₁ = 0.0177, and wR₂ = 0.0288 for HP‐EuOF. Calculations of the bond valence sums clearly showed that the oxygen atoms occupy the tetrahedrally coordinated position, whereas the fluorine atoms are fivefold coordinated in form of distorted square‐pyramids. The crystal structures and properties of HP‐REOF (RE = Nd, Sm, Eu) are discussed and compared to the isostructural phases and the normal‐pressure modifications of REOF (RE = Nd, Sm, Eu). Furthermore, results of investigations by EDX and Raman measurements including quantum mechanical calculations are presented.     

Two Hexagonal Series of Lanthanoid(III) Oxide Fluoride Selenides: M6O2F8Se3 (M = La – Nd) and M2OF2Se (M = Nd,Sm, Gd – Ho)

Two hexagonal series of lanthanoid(III) oxide fluoride selenides with similar structure types can be obtained by the reaction of the components MF₃, M₂O₃, M, and Se in sealed niobium tubes at 850 °C using CsI as fluxing agent. The compounds with the lighter and larger representatives (M = La – Nd) occur with the formula M₆O₂F₈Se₃, whereas with the heavier and smaller ones (M = Nd, Sm, Gd – Ho) their composition is M₂OF₂Se. For both systems single‐crystal determinations were used in all cases. The compounds crystallize in the hexagonal crystal system (space group: P6₃/m) with lattice parameters of a = 1394–1331 pm and c = 403–372 pm (Z = 2 for M₆O₂F₈Se₃ and Z = 6 for M₂OF₂Se). The (M1)³⁺ cations show different square antiprismatic coordination spheres with or without an extra capping fluoride anion. All (M2)³⁺ cations exhibit a ninefold coordination environment shaped as tricapped trigonal prism. In both structure types the Se^2– anions are sixfold coordinated as trigonal prisms of M³⁺ cations, being first condensed by edges to generate trimeric units and then via faces to form strands running along [001]. The light anions reside either in threefold triangular or in fourfold tetrahedral cationic coordination. For charge compensation, both structures have to contain a certain amount of oxide besides fluoride anions. Since F^– and O^2– can not be distinguished by X‐ray diffraction, bond‐valence calculations were used to address the problem of their adjunction to the available crystallographic sites.     

The Heterometallic Clusters of Trivalent Rare Earth Metals of [Ln(OPh)6{Li(dme)}3], with Ln=Eu and Sm

Two new heterobimetallic phenoxide Ln^III–Li complexes of formula [Ln(μ₂‐OPh)₆{Li(dme)}₃] (Ln=Sm, Eu) have been synthesized and characterized using single‐crystal X‐ray diffraction. These two compounds are isostructural.     

Nitrides with Inverse K2[NiF4] Structure: (R1–xCa3+xN1–x/3)Bi2 with R = Rare‐Earth Metal

The novel nitrides (R_1–xCa_3+xN_1–x/3)Bi₂ (with R = La, Ce, Pr) crystallize in the K₂[NiF₄] structure type (I4/mmm, No. 139, Z = 2). Samples (La_1–xCa_3+xN_1–x/3)Bi₂ with x = 0.10, 0.05, 0.00, (Ce_1–xCa_3+xN_1–x/3)Bi₂ with x = 0.30, and (PrCa₃N)Bi₂ were obtained as single phase microcrystalline powders according to X‐ray diffraction and the crystal structure details were derived from Rietveld refinements based on X‐ray and neutron diffraction powder patterns. A partial order of R³⁺/Ca²⁺ on two crystallographic sites is governed by different ionic radii and charges. (La_1–xCa_3+xN_1–x/3)Bi₂ and (Ce_1–xCa_3+xN_1–x/3)Bi₂ exhibit small homogeneity ranges and typically a nitrogen deficiency. In contrast, for (PrCa₃N)Bi₂ no indications for a significant homogeneity range or deficiency of nitrogen was observed. (La_1–xCa_3+xN_1–x/3)Bi₂ with x = 0.05 is a diamagnet. X‐ray absorption spectroscopy at the CeL₃‐edge as well as magnetic susceptibility measurements evidence that (Ce_1–xCa_3+xN_1–x/3)Bi₂ with x = 0.30 contains Ce³⁺ in the 4f¹ configuration. According to electrical resistivity data, samples from all three systems are heavily doped semiconductors.     

Synthesis and Crystal Structure of Tetrakis(tetramethylammonium) Bis[decabromotetraselenate(II)]‐bis[dibromodiselenate(I)], [(CH3)4N]4[(Se4Br10)2(Se2Br2)2], the Salt of a Mixed‐Valence Bromoselenate(II/I) Anion

Brown crystals of [NMe₄]₄[(Se₄Br₁₀)₂(Se₂Br₂)₂] ( 1 ) were obtained from the reaction of selenium and bromine in acetonitrile in the presence of tetramethylammonium bromide. The crystal structure of 1 was determined by X‐ray diffraction and refined to R = 0.0297 for 8401 reflections. The crystals are monoclinic, space group P2₁/c with Z = 4 and a = 12.646(3) Å, b = 16.499(3) Å, c = 16.844(3) Å, β = 101.70(3)° (123 K). In the solid‐state structure, the anion of 1 is built up of two [Se₄Br₁₀]^2– ions. Each shows a triangular arrangement of three planar SeBr₄ units sharing a common edge through two μ₃‐bridging bromine atoms, and one SeBr₂ molecule, which is linked to the Se^II atoms of two SeBr₄ units; between the Se₄Br₁₀^2– ions a dimerized Se₂Br₂ molecule (Se₄Br₄) is situated and one Se^I atom of each Se₂Br₂ molecule has two weak contacts [3.3514(14) Å and 3.3952(11) Å] to two bromine atoms of one SeBr₄ unit. Four Se^I atoms of a dimerized Se₂Br₂ molecule are in a almost regular planar tetraangular arrangement. Contacts between the Se^II atom of the SeBr₂ molecule and the Se^II atoms of two SeBr₄ units are 3.035(1) Å and 3.115(1) Å, and can be interpreted as donor‐acceptor type bonds with the Se^II atoms of SeBr₄ units as donors and the SeBr₂ molecule as acceptor. The terminal Se^II–Br and μ₃‐Br–Se^II bond lengths are in the ranges 2.3376(10) to 2.4384(8) Å and 2.8036(9) to 3.3183(13) Å, respectively. The bond lengths in the dimerized Se₂Br₂ molecule are: Se^I–Se^I = 2.2945(8) Å and 3.1398(12), Se^I–Br = 2.3659(11) and 2.3689(10) Å.     

The Ternary Lanthanoid Nickel Arsenides Tb12Ni30As21 and Dy12Ni30As21 with (La,Ce)12Rh30P21 Type Related Structure

The title compounds were synthesized from the elements by reactions at high temperature. They crystallize with a hexagonal structure which was determined from single‐crystal X‐ray data of Dy₁₂Ni₃₀As₂₁: P6₃/m, Z = 1, a = 1698.5(5) pm, c = 387.7(1) pm, R = 0.053 for 797 F values and 69 variable parameters. It belongs to a large family of hexagonal structures with a metal to metalloid ratio of 2 : 1. In these hexagonal structures an ordered distribution of occupied atomic positions around the hexagonal 6₃ axis is possible only for refinements in space groups of lower symmetry. This is discussed for the present case and the very closely related structures reported for (La, Ce)₁₂Rh₃₀P₂₁ and Nd₃Ni₇P₅.     

New Intermetallic Compounds Ln2Ni2Mg (Ln = Y,La–Nd,Sm, Gd–Tm) with Mo2FeB2 Structure

The title compounds were synthesized by reacting the elements in sealed tantalum tubes in a high‐frequency furnace. They crystallize with the Mo₂FeB₂ structure, a ternary ordered variant of the U₃Si₂ type, space group P4/mbm. All compounds were characterized through Guinier powder patterns and the lattice parameters were obtained from least‐squares fits. Four structures were refined from single crystal X‐ray data: a = 740.5(1) pm, c = 372.5(1) pm, wR2 = 0.0430, 247 F values, 13 variables for Y₂Ni_1.90Mg, a = 764.5(1) pm, c = 394.39(9) pm, wR2 = 0.0371, 310 F values, 12 variables for La₂Ni₂Mg, a = 754.4(1) pm, c = 385.20(9) pm, wR2 = 0.0460, 295 F values, 12 variables for Pr₂Ni₂Mg, and a = 752.53(8) pm, c = 382.33(5) pm, wR2 = 0.0183, 291 F values, and 12 variables for Nd₂Ni₂Mg. A refinement of the occupancy parameters indicated small defects on the nickel site of the yttrium compound, resulting in the composition Y₂Ni_1.90Mg for the investigated single crystal. The compounds with cerium, samarium, and gadolinium to thulium as rare earth component were characterized through their Guinier powder patterns. The cell colume of Ce₂Ni₂Mg is smaller than that of Pr₂Ni₂Mg, indicating intermediate‐valent cerium. The structures can be considered as an intergrowth of distored AlB₂ and CsCl related slabs of compositions LnNi₂ and LnMg. Chemical bonding in La₂Ni₂Mg and isotypic La₂Ni₂In is compared on the basis of extended Hückel calculations.     

Rare earth-rich cadmium compounds RE 4 TCd (T = Co, Ru, and Rh) with Gd4RhIn type structure

The rare earth-rich cadmium compounds RE ₄ TCd (RE = Y, La–Nd, Sm, and Gd–Tm, Lu; T = Co, Ru, and Rh) were prepared from the elements in sealed tantalum ampoules in an induction furnace. All samples were characterized by X-ray powder diffraction. The structures of Y₄RuCd (a = 1362.5(1) pm), La₄RuCd (a = 1415.9(1) pm), Gd₄RuCd (a = 1368.8(2) pm), La₄CoCd (a = 1417.9(4) pm), Gd₄CoCd (a = 1356.1(1) pm), and Gd₄RhCd (a = 1368.7(1) pm) were refined from single crystal X-ray diffractometer data. The RE ₄ TCd compounds crystallize with the cubic Gd₄RhIn type structure, space group F ${\bar 4}The rare earth-rich cadmium compounds RE ₄ TCd (RE = Y, La–Nd, Sm, and Gd–Tm, Lu; T = Co, Ru, and Rh) were prepared from the elements in sealed tantalum ampoules in an induction furnace. All samples were characterized by X-ray powder diffraction. The structures of Y₄RuCd (a = 1362.5(1) pm), La₄RuCd (a = 1415.9(1) pm), Gd₄RuCd (a = 1368.8(2) pm), La₄CoCd (a = 1417.9(4) pm), Gd₄CoCd (a = 1356.1(1) pm), and Gd₄RhCd (a = 1368.7(1) pm) were refined from single crystal X-ray diffractometer data. The RE ₄ TCd compounds crystallize with the cubic Gd₄RhIn type structure, space group F 3m. The transition metal atoms have tricapped trigonal prismatic rare earth coordination. The trigonal prisms are condensed via common edges, forming a rigid three-dimensional network with adamantane symmetry. Voids in these networks are filled by Cd₄ tetrahedra (304 pm Cd–Cd in Gd₄CoCd) and polyhedra of the RE1 atoms. The crystal chemical peculiarities are briefly discussed. Correspondence: Rainer P?ttgen, Institut für Anorganische und Analytische Chemie, Westf?lische Wilhelms-Universit?t Münster, Correnstrasse 30, 48149 Münster, Germany.     

Crystal Structure of the RE2PbS4 (RE = Y,Dy, Ho,Er, and Tm) Compounds and a Comparison with the Crystal Structures of other Rare Earth Lead Chalcogenides

The crystal structure of the RE₂PbS₄ (RE = Y, Dy, Ho, Er and Tm) compounds (space group Cmc2₁, Pearson symbol oC112, a = 0.79301(3) nm, b = 2.86966(9) nm, c = 1.20511(5) nm, R_Bragg = 0.0979 for Y₂PbS₄; a = 0.79484(8) nm, b = 2.8721(3) nm, c = 1.2039(1) nm, for Dy₂PbS₄; a = 0.79081(2) nm, b = 2.86222(7) nm, c = 1.20220(4) nm, R_Bragg = 0.0859 for Ho₂PbS₄; a = 0.7863(2) nm, b = 2.8525(5) nm, c = 1.1995(2) nm, R1 = 0.0482 for Er₂PbS₄ and a = 0.78419(3) nm, b = 2.84184(9) nm, c = 1.19655(4) nm, R_Bragg = 0.0893 for Tm₂PbS₄) was investigated by means of X‐ray single crystal and powder diffraction. Each RE atoms is octahedrally coordinated by six S atoms. Each Pb atoms is surrounded by seven S atoms to form a mono‐capped trigonal prism.