Nd4.67Ru3Mg8.83 – A Magnesium‐rich Compound with Ru@Mg4Nd4 Square Antiprisms and Mg@Mg8 Cubes as ­Basic Building Units

The magnesium‐rich intermetallic compound Nd_4.67Ru₃Mg_8.83 was synthesized from the elements in a sealed tantalum tube in a resistance furnace. Nd_4.67Ru₃Mg_8.83 was characterized by X‐ray powder and single crystal diffraction: new structure type,I4/mmm, tI66, a = 946.0(1), c = 1789.5(4) pm, wR2 = 0.0368, 725 F² values and 36 variables. Two of the five crystallographically independent magnesium sites show a small degree of Mg/Nd mixing. The ruthenium atoms have square anti‐prismatic Nd₄Mg₄ coordination. Always six of such anti‐prisms are condensed via common edges, leading to a CsCl analogous neodymium coordination for the Mg4 atoms. The two‐dimensional networks of edge‐sharing Ru@Nd₄Mg₄ antiprisms are condensed to a three‐dimensional network via Mg5@Mg3₄Mg1₄ cubes. The extended magnesium substructure shows a broad range of Mg–Mg distances from 308 to 351 pm.     

Binäre Lanthan‐Stannide mit Sn:La‐Verhältnissen nahe 1:1 – Synthesen,Kristallstrukturen, Chemische Bindung

Four binary lanthanum stannides close to the 1:1 ratio of Sn:La were synthesized from mixtures of the elements. The structures of the compounds have been determined by means of single‐crystal X‐ray data. The low temperature (α) form of LaSn (CrB‐type, orthorhombic, space group Cmcm, a = 476.33(6), b = 1191.1(2), c = 440.89(6) pm, Z = 4, R1 = 0.0247), crystallizes with the CrB‐type. The structure exhibits planar tin zigzag chains with a Sn–Sn bond length of 299.1 pm. In contrast to the electron precise Zintl compounds of the alkaline earth elements, additional La–Sn bonding contributions become apparent from the results of band structure calculations. In the somewhat tin‐richer region, the new compound La₃Sn₄ (orthorhombic, space group Cmcm, a = 451.45(4), b = 1190.44(9), c = 1583.8(2) pm, Z = 4, R1 = 0.0674), crystallizing with the Er₃Ge₄ structure type, exhibits Sn₃ segments of the zigzag chains of α‐LaSn together with a further Sn atom in a square planar Sn coordination with increased Sn–Sn bond lengths. In the Lanthanum‐richer region, La₁₁Sn₁₀ (tetragonal, space group I4/mmm, a = 1208.98(5), c = 1816.60(9) pm, Z = 4, R1 = 0.0325) forms the undistorted tetragonal Ho₁₁Ge₁₀ structure type. Its structure, which contains isolated Sn atoms, [Sn₂] dumbbells and planar [Sn₄] rings is related to the high temperature (β) form of LaSn. The structure of β‐LaSn (space group Cmmm, a = 1766.97(6), b = 1768.28(5), c = 1194.32(3) pm, Z = 60, R1 = 0.0453), which forms a singular structure type, can be derived from that of La₁₁Sn₁₀ by the removal of thin slabs. Due to the different stacking of the remaining layers, planar [Sn₄] chain segments and linear [Sn–Sn–Sn] anions are formed as additional structural elements. The chemical bonding (Sn–Sn covalent bonding, Sn–La contributions) is discussed on the basis of the simple Zintl concept and the results of FP‐LAPW calculations (density of states, band structure, valence electron densities and electron localization function).     

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.     

Ternary Rhodium Borides A3Rh5B2 (A = Mg,Sc) and Quaternary Derivatives A2MRh5B2. Preparation,Crystal Structure (M = Main Group and 3 d Elements), and Magnetism (M = Mn,Fe)

The new ternary rhodium borides Mg₃Rh₅B₂ and Sc₃Rh₅B₂ (P4/mbm, Z = 2; a = 943.4(1) pm, c = 292.2(1) pm and a = 943.2(1) pm, c = 308.7(1) pm, respectively) crystallize with the Ti₃Co₅B₂ type structure. Mg and Sc may in part be substituted by a variety of elements M. For M = Si and Fe, homogeneity ranges were found according to A_3–xM_xRh₅B₂ with 0 ≤ x ≤ 1.0 for A = Sc and with x up to 1.5 for A = Mg. Quaternary compounds with x = 1 (A₂MRh₅B₂: A/M in short) were prepared with M = Be, Al, Si, P, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Sn (Co, Ni only with A = Mg; Sn only with A = Sc; P, As with deficiencies). Single crystal X‐ray investigations show an ordered substitutional variant of the Ti₃Co₅B₂ type in which the M atoms are arranged in chains along [001] with intrachain and interchain M–M distances of about 300 pm and 660 pm, respectively. Measuring the magnetisation (1.7 K–800 K) of the phases Mg/Mn, Sc/Mn, Mg/Fe, and Sc/Fe reveals antiferromagnetic interactions in the first and dominating ferromagnetic intrachain interactions in the remaining ones. Interchain interactions of antiferromagnetic nature are evident in Sc/Mn and Mg/Fe leading to metamagnetism below T_N = 130 K, while Sc/Fe behaves ferromagnetically below T_C = 450 K. The overall trend towards stronger ferromagnetic interactions with increasing valence electron concentration is obvious.     

The crystal structure of Mg51Zn20

The crystal structure of Mg₅₁Zn₂₀, a phase designated conventionally as “Mg₇Zn₃,” has been determined by the single-crystal X-ray diffraction method. It was solved by the examination of a Patterson synthesis, and refined by the ordinary Fourier and least-squares method; the R value obtained was 4.8% for 1167 observed reflections. The crystal is orthorhombic, space group Immm, with a = 14.083(3), b = 14.486(3), c = 14.025(3) Å, and Z = 2. There are 18 independent atomic sites, Zn1Zn6, Mg1Mg10, A, and B, and the last two sites are statistically occupied by Zn and Mg atoms with the occupancies; 0.46(2)Zn7 + 0.52(2)Mg11 and 0.24(2)Zn8 + 0.74(2)Mg12, for A and B, respectively. The structure of the crystal is described as an arrangement of icosahedral coordination polyhedra, to which all the atomic sites but Zn3 site belong. In this arrangement the Zn atoms other than the Zn3 and Zn8(B) center the icosahedral coordination polyhedra with coordination number 12. The Zn3, Zn8 atoms, and all the Mg atoms except Mg11(A) are located at the centers of various coordination polyhedra with the coordination numbers from 11 to 15. The distances between neighboring atoms are 2.71–3.07, 2.82–3.65, and 2.60–3.20 Å for ZnZn, MgMg, and ZnMg, respectively.     

Ce20Mg19Zn81: a new structure type with a giant cubic cell

Icosacerium nonadecamagnesium henoctacontazinc, Ce₂₀Mg₁₉Zn₈₁, synthesized by fritting of the pure elements with subsequent arc melting, crystallizes with an unusually large cubic unit cell [space group F3m, a = 21.1979 (8) Å] and represents a new structure type among the technologically important family of ternary rare earth–transition metal–magnesium intermetallics. The majority of atoms (two Ce and five Zn) display .3m site symmetry, two Ce and one Mg atom occupy three 2.mm positions, one Mg and one Zn have 3m site symmetry, one Mg and three Zn atoms sit in ..m positions, and one Zn atom is in a general position. The Ce₂₀Mg₁₉Zn₈₁ structure can be described using the geometric concept of nested polyhedral units, by which it consists of four different polyhedral units, viz.A (Zn+Zn₄+Zn₄+Zn₁₂+Ce₆), B (Mg+Zn₁₂+Ce₄+Zn₂₄+Ce₄), C (Zn₄+Zn₁₂+Mg₆) and D (Zn₄+Zn₄+Mg₁₂+Ce₆), with the outer construction unit being an octahedron or tetrahedron. All interatomic distances in the structure indicate metallic‐type bonding.     

Crystal Structure of ϵ‐Ag7+xMg26–x – A Binary Alloy Phase of the Mackay Cluster Type

The binary alloy phase ϵ‐Ag_7+xMg_26–x with x ≈ 1 and small amounts of the β′‐AgMg phase crystallize by annealing of Ag–Mg alloys with starting compositions between 24–28 At‐% Ag at 390 to 420 °C. A model structure for the ϵ‐phase consisting of a fcc packing of Mackay clusters was derived from the known structure of the ϵ′‐Ag₁₇Mg₅₄ phase. Crystals of the ϵ‐phase were obtained by direct melting of the elements and annealing. The examination of a single crystal yielded a face‐centered cubic unit cell, space group Fm3 with a = 1761.2(5) pm. The refinement was started with the parameters of the model: wR2(all) = 0.0925 for 1093 symmetrically independent reflections. A refinement of the occupancy parameters indicated a partial replacement of silver for magnesium at two metal atom sites, resulting in the final composition ϵ‐Ag_7+xMg_26–x with x = 0.96(2). There are 264 atoms in the unit cell and the calculated density is 3.568 gcm^–3. The topology of the model was confirmed. Mackay icosahedra are located at the lattice points of a face‐centered cubic lattice. Differences between model and refined structure and their effects on the powder patterns are discussed. The new binary structure type of ϵ‐Ag_7+xMg_26–x can be described in terms of the I3‐cluster concept.     

Isotype Borophosphate MII(C2H10N2)[B2P3O12(OH)] (MII = Mg,Mn, Fe,Ni, Cu,Zn): Verbindungen mit Tetraeder‐Schichtverbänden

Isotypic Borophosphates M^II(C₂H₁₀N₂)[B₂P₃O₁₂(OH)] (M^II = Mg, Mn, Fe, Ni, Cu, Zn): Compounds containing Tetrahedral Layers The isotypic compounds M^II(C₂H₁₀N₂) · [B₂P₃O₁₂(OH)] (M^II = Mg, Mn, Fe, Ni, Cu, Zn) were prepared under hydrothermal conditions (T = 170 °C) from mixtures of the metal chloride (chloride hydrate, resp.), Ethylenediamine, H₃BO₃ and H₃PO₄. The orthorhombic crystal structures (Pbca, No. 61, Z = 8) were determined by X‐ray single crystal methods (Mg(C₂H₁₀N₂)[B₂P₃O₁₂(OH)]: a = 936.81(2) pm, b = 1221.86(3) pm, c = 2089.28(5) pm) and Rietveld‐methods (M^II = Mn: a = 931.91(4) pm, b = 1234.26(4) pm, c = 2129.75(7) pm, Fe: a = 935.1(3) pm, b = 1224.8(3) pm, c = 2088.0(6) pm, Ni: a = 939.99(3) pm, b = 1221.29(3) pm, c = 2074.05(7) pm, Cu: a = 941.38(3) pm, b = 1198.02(3) pm, c = 2110.01(6) pm, Zn: a = 935.06(2) pm, b = 1221.33(2) pm, c = 2094.39(4) pm), respectively. The anionic part of the structure contains tetrahedral layers, consisting of three‐ and nine‐membered rings. The M^II‐ions are in a distorted octahedral or tetragonal‐bipyramidal [4 + 2] (copper) coordination formed by oxygen functions of the tetrahedral layers. The resulting three‐dimensional structure contains channels running along [010]. Protonated Ethylenediamine ions are fixed within the channels by hydrogen bonds.     

Syntheses and Crystal Structures of LaRhMg,CeRhMg, PrRhMg,and NdRhMg

New intermetallic rare earth compounds LaRhMg, CeRhMg, PrRhMg, and NdRhMg were prepared by reaction of the elements in sealed tantalum tubes in a high‐frequency furnace. The compounds were investigated by X‐ray diffraction both on powders and single crystals. LaRhMg crystallizes with the LaNiAl type structure, space group Pnma, Z = 8, a = 760.1(2), b = 419.92(8), c = 1702.6(2) pm, wR2 = 0.0482, 740 F² values and 38 variable parameters. The cerium compound adopts the ZrNiAl structure: P6¯2m, Z = 3, a = 752.3(1), c = 417.6(1) pm, wR2 = 0.0497, 250 F²2 values and 17 variable parameters. PrRhMg and NdRhMg crystallize with the TiNiSi type: Pnma, Z = 4, a = 721.62(7), b = 415.98(4), c = 869.47(8) pm, wR2 = 0.1864, 440 F² values, 20 variables for PrRhMg and a = 720.6(1), b = 417.6(1), c = 868.8(1) pm, wR2 = 0.0779, 425 F² values, 22 variables for NdRhMg. Refinements of the occupancy parameters revealed mixed Mg/Rh occupancy for the magnesium sites of the cerium and the neodymium compound leading to the compositions CeRh_1.262(8)Mg_0.738(8) and NdRh_1.114(9)Mg_0.886(9) for the investigated single crystals. From a geometrical point of view, the four crystal structures are built up from different rhodium centered trigonal prisms. The rhodium and magnesium atoms form three‐dimensional [RhMg] networks in which the rare earth metal atoms are located in different types of channels. The networks show Rh—Mg and Mg—Mg bonding.     

Zn-Mg合金的结构分析和Zn-Mg扩散体系的物相分布

分子动力学(MD)模拟常采用径向分布函数(RDF)、Honeycutt-Anderson (HA)键型指数法、原子团类型指数法(CTIM)表征物相的微观结构. 本文依据CTIM 理论, 对CTIM 进一步发展, 使CTIM 不仅能够表征bcc\fcc\hcp\非晶体, 也能表征其它晶系的晶体结构. 本文采用CTIM 完成Zn-Mg 合金标准晶体的结构表征和Zn-Mg扩散体系物相分布的分析. 结果表明: 合金组元的CTIM指数不仅反映了Mg₂₁Zn₂₅、MgZn₂、Mg₂Zn₁₁晶体结构的差异, 也说明了Mg₄Zn₇、MgZn₂晶体结构十分相近. Zn-Mg扩散体系两步法模拟后, 体系两端交替分布着hcp 与fcc 结构; 体系中部形成大量的非晶体; Zn原子端交替分布着hcp 与fcc 结构的界面区域主要是Zn12-C类原子.     

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.     

Zn5Ir7B3, Zn5Rh7B3 und Zn7+xRh9–xB3 (x ≈ 0,4) – neue ternäre Zink‐Platinmetallboride

Zn₅Ir₇B₃, Zn₅Rh₇B₃, and Zn_7+xRh_9–xB₃ (x ≈ 0.4) – New Ternary Zinc Platinum Metal Borides The new ternary zinc borides Zn₅Ir₇B₃, Zn₅Rh₇B₃, and Zn_7+xRh_9–xB₃ (x ≈ 0.4) were prepared by reaction of the elemental components at temperatures in the range 1200 to 1230 ?C. They crystallize orthorhombically in the space group Pmma with Z = 2. Zn₅Ir₇B₃ (a = 1116.1(2) pm, b = 284.96(4) pm, c = 1178.1(2) pm; R = 0.042, 1414 reflections, 47 parameters) and Zn₅Rh₇B₃ (a = 1101.6(2) pm, b = 283.94(3) pm, c = 1166.6(4) pm, R = 0.033, 787 reflections, 47 parameters) are isotypic. Along the short axis planar nets of platinum metal atoms at y = 0 alternate with layers containing the boron and zinc atoms at z = ¹/₂. By the stacking of the platinum metal nets columns of trigonal prisms centered by boron atoms, columns of pentagonal prisms containing zinc atoms and channels with horse shoe shaped cross sections, all running along the b‐axis are formed. The latter are filled by an aggregation of zinc atoms consisting of four parallel rows. In the structure of Zn_7+xRh_9–xB₃ (a = 1117.1(3) pm, b = 285.38(8) pm, c = 1484.8(5) pm; R = 0.026, 975 reflections, 59 parameters) one of the sitesets is occupied by Rh and Zn atoms approximately in the ratio 6 : 4. The structure contains the same building elements as those found in Zn₅Rh₇B₃ and in addition Rh prisms with elongated hexagon cross sections accommodating pairs of zinc atoms. These prisms are connected by common faces to form layers perpendicular to the c axis.     

Mg3Ir3Si8, ein neues Magnesium‐Iridium‐Silicid mit Tetraedern und gekappten Tetraedern aus Silicium‐Atomen

Mg₃Ir₃Si₈, a New Magnesium Iridium Silicide with Si₄ Tetrahedra and Si₁₂ Truncated Tetrahedra The ternary silicide Mg₃Ir₃Si₈ (cubic, a = 1221.4(1) pm, space group , 8 formula units per unit cell) was prepared by reaction of the elemental components in a sealed molybdenum container (1000 °C, 1 d, cooled with 100 °/h). The crystal structure was determined from single crystal data. Short distances in the three‐dimensional iridium silicon network indicate strong Ir‐Si‐bonding (d(Ir‐Si) = 240.5(2) and 245.6(1) pm). In addition, homonuclear bonding seems to be important, resulting in the formation of Si₄‐tetrahedra (d(Si‐Si) = 257(1) pm), and Mg centered Si₁₂‐polyhedra with the shape of truncated tetrahedra (d(Si‐Si) = 241(1) and 261.0(9) pm). Furthermore, Mg₄‐tetrahedra with Mg‐Mg‐distances of 355(2) pm are formed. The structure may be derived from the structure of the isotypic compounds Mg₅Pd₁₀Si₁₆ and Mg₅Pt₁₀Si₁₆ by adding a Mg siteset and subtracting a platinum metal siteset. It can be described by an expanded cubic “close” packing of MgIr₆‐octahedra in which Si₄‐tetrahedra reside in the octahedral holes while Mg₄‐tetrahedra and MgSi₁₂‐units occupy one half of the tetrahedral holes each.     

K13CoSn17–x (x = 0.1): A New Ternary Phase Containing ­Cobalt Centered [Sn9] Cluster Synthesized via High‐Temperature Reaction

A new ternary potassium cobalt stannide, K₁₃CoSn_17–x (x = 0.1), was obtained by reacting the mixture of the corresponding pure elements at high temperature, and structurally characterized by single‐crystal X‐ray diffraction study. K₁₃CoSn_17–x (x = 0.1) crystallizes in the orthorhombic space group Pbca (No. 61) with a = 26.2799(7) Å, b = 24.1541(6) Å, c = 29.8839(6) Å, V = 18969.3(8) ų, and Z = 16. Its structure contains isolated [CoSn₉] monocapped square antiprism and [Sn₄] tetrahedron in the ratio 1:2, forming a hierarchical variant of Laves phase MgZn₂. The structural relation between the title compound with MgZn₂ as well as other binary stannides is also discussed.     

About Binary and Ternary Alkaline Earth Metal Nitrides

Binary and ternary alkaline earth metal nitrides compounds have been synthesized and characterized by the means of X‐ray structure analysis. By the reaction of the alkaline earth metals Be, Mg, and Ca with dry nitrogen, we obtained crystalline material of Be₃N₂ ( 1 ), Mg₃N₂ ( 2 ), and Ca₃N₂ ( 3 ), respectively. For these three compounds we could confirm the cubic anti bixbyite structure (Ia3 (#206); 1 : a = 814.92(1) pm; 2 : 997.26(6) pm and 3 : a = 1147.86(2) pm). By reacting 1 : 2 : 1 mixtures of Ae (Ae = Ca, Sr) : Mg : NaN₃ we synthesized the ternary nitrides CaMg₂N₂ ( 4 ) and SrMg₂N₂ ( 5 ). We confirmed the structural data obtained by Rietveld‐analysis of X‐ray powder diffraction data for 4 and found 5 to be isotypic (anti‐C–M₂O₃ structure, trigonal, P 3ml (#164); 4 : a = 354.77(5) pm, c = 609.60(12) pm; 4 : a = 362.20(5), c = 635.90(13) pm). The indexing of the powder diffractogram of “Ca₃Mg₃N₄” and refining the lattice parameters (hexagonal, a = 352.9(2) and c = 607.5(5) pm) suggest its identity with 4 . The black “low‐temperature phase of Ca₃N₂” has been synthesized and and the X‐ray powder diffractogram has been recorded. The reactions of this phase are also described. The yellow “high‐temperature phase of Ca₃N₂” was found to be Ca₄N₂(CN₂).     

Modeling of half-Heusler crystals with the chalcopyrite structure: Li<Subscript>2</Subscript>MgZn<Emphasis Type="Italic">X</Emphasis><Subscript>2</Subscript> (X = N,P, As,Sb)

A model of Li₂MgZnX ₂ half-Heusler compounds with the chalcopyrite structure is considered. The electronic structure is studied from first principles, showing that Li₂MgZnX ₂ are direct-gap crystals, except for pseudo-direct-gap Li₂MgZnP₂, with a band gap of 2.7 eV, 2.2 eV, 3.3 eV, and 2.5 eV for X = N, P, As, and Sb, respectively. The band structure and chemical bonding in the model crystals are found to be similar to those in LiMgX and LiZnX half-Heusler crystals. Total electron density and deformation electron density distributions are obtained. It is found that Mg–X and Zn–X ionic-covalent bonds are stronger than Li–X ionic bonds in Li₂MgZnX ₂ crystals, which allows Li atoms to move in the space between MgX ₄ and ZnX ₄ cation tetrahedra.     

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.     

Intermetallic Gold Compounds REAuMg (RE = Y,La–Nd,Sm, Eu,Gd–Yb)

New intermetallic rare earth compounds REAuMg (RE = Y, La–Nd, Sm, Eu, Gd–Yb) were synthesized by reaction of the elements in sealed tantalum tubes in a high‐frequency furnace. The compounds were investigated by X‐ray diffraction both on powders and single crystals. Some structures were refined on the basis of single crystal data. The compounds with Y, La–Nd, Sm, and Gd–Tm adopt the ZrNiAl type structure with space group P62m: a = 770.8(2), c = 419.5(1) pm, wR2 = 0.0269, 261 F² values for PrAuMg, a = 750.9(2), c = 407.7(1) pm, wR2 = 0.0561, 649 F² values for HoAuMg with 15 variables for each refinement. Geometrical motifs in HoAuMg are two types of gold centered trigonal prisms: [Au1Mg₃Ho₆] and [Au2Mg₆Ho₃]. The gold and magnesium atoms form a three‐dimensional [AuMg] polyanion in which the holmium atoms fill distorted hexagonal channels. The magnesium positions show a small degree of magnesium/gold mixing resulting in the refined compositions PrAu_1.012(2)Mg_0.988(2) and HoAu_1.026(3)Mg_0.974(3). EuAuMg and YbAuMg contain divalent europium and ytterbium, respectively. Both compounds crystallize with the TiNiSi type structure, space group Pnma: a = 760.6(3), b = 448.8(2), c = 875.8(2) pm, wR2 = 0.0491, 702 F² values, 22 variables for EuAuMg, and a = 738.4(1), b = 436.2(1), c = 864.6(2) pm, wR2 = 0.0442, 451 F² values, and 20 variables for YbAuMg. The europium position shows a small degree of europium/magnesium mixing, and the magnesium site a slight magnesium/gold mixing leading to the refined composition Eu_0.962(3)Au_1.012(3)Mg_1.026(3). No mixed occupancies were found in YbAuMg where all sites are fully occupied. In these structures the europium(ytterbium) and magnesium atoms form zig‐zag chains of egde‐sharing trigonal prisms which are centered by the gold atoms. As is typical for TiNiSi type compounds, also in EuAuMg and YbAuMg a three‐dimensional [AuMg] polyanion occurs in which the europium(ytterbium) atoms are embedded. The degree of distortion of the two polyanions, however, is different.     

Yb6Ir5Ga7 – A MgZn2 Superstructure

The gallide Yb₆Ir₅Ga₇ was synthesized by high‐frequency melting of the elements in a sealed niobium ampoule. The structure was refined from single‐crystal X‐ray diffractometer data: Nb_6.4Ir₄Al_7.6 type, P6₃/mcm, a = 930.4(1), c = 843.0(1) pm, wR₂ = 0.0597, 379 F² values and 22 variables. Yb₆Ir₅Ga₇ adopts a superstructure of the MgZn₂ Laves phase by a complete ordering of the iridium and gallium atoms on the zinc substructure, i.e. the network consists of ordered and condensed Ir₃Ga and IrGa₃ tetrahedra with Ir–Ga distances ranging from 260 to 265 pm. The crystal chemical details and the underlying group‐subgroup scheme are discussed.     

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.