Marco Wendorff

Synthesis and crystal structure of the tetrelides A12M17 (A=Na, K, Rb, Cs; M=Si, Ge, Sn) and A4Pb9 (A=K, Rb)

Abstract A series of different compounds of stoichiometries A I 12 M IV 17 (A I =Na, K, Rb, Cs; M IV =Si, Ge, Sn) and A I 4 M 9 IV (A I =K, Rb; M IV =Pb) were synthesized from the elements and their crystal structures determined on the basis of single crystal X-ray data. In the compounds A 4 Pb 9 (A=K/Rb; monoclinic, space group P 2 1 / m , a =960.1(9)/989.4(9), b =1319.0(12)/1340.6(12), c =1582.3(14)/1624.3(14) pm, 103.19(2)/103.23(2)°, R1=0.0674/0.0674) the Pb atoms form isolated Wade nido clusters [Pb 9 ] 4− of approximate C 4 v symmetry (monocapped square antiprisms), which are arranged in a hexagonal closed packing and are separated by the A cations. Similar cluster anions M 9 4− (M=Si, Sn) are present in the compounds K 12 Si 17 (monoclinic, space group P 2 1 / c , a =2368.9(3), b =1357.2(2), c =4450.9(6), β =91.248(4)°, Z =4) and Rb 12 Sn 17 (orthorhombic, space group P 2 1 2 1 2 1 , a =1504.1(6), b =1539.34(12), c =2147.8(2) pm, Z =4) which can formally be described by an ionic decomposition into K/Rb cations and two Zintl anions [M 4 ] 4− (M=Si, Sn; isosteric with white phosphorus) and one [M 9 ] 4− cluster. The two compounds represent examples of hierarchical variants of the Laves phases MgZn 2 and MgCu 2 , respectively. A number of additional members of the series A I 12 M IV 17 have been prepared, and both spectroscopic and preliminary X-ray crystallographic data could be obtained for them.

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

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.

Das neue komplexe Barium-Mercurid Ba20Hg103 und seine ternären Zink- und Cadmium-Varianten / The New Complex Barium Mercuride Ba20Hg103 and its Ternary Zinc and Cadmium Variants

Ba20Hg103, the next Hg-rich binary barium mercuride after BaHg11 and BaHg6, was synthesized from melts of the elements, which were slowly cooled from 550 to 200 °C. It forms a new complex cubic structure type (F43m, a = 2333.30(10) pm, Z = 4, R1 = 0.0651) with four Ba und 13 Hg positions as determined by means of single-crystal X-ray diffraction. The structure can be best described by decomposing it into four types (A to D) of space-filling distorted truncated octahedra (sodalite or b-cages) centered at the four sites with 43m point group symmetry of the space group. The cages C and D are centered by [Hg8] tetrahedra stars, which are connected via [Hg(13)Hg8] cubes to form a diamond-type network. The polyhedra B contain a section of the Laves phaseMgCu2 (five [Hg4] tetrahedra sharing corners). The smallest polyhedron A contains a truncated tetrahedron [HgHg12] surrounded by a strongly covalently bonded mercury shell. The ternary cadmium derivative Ba20Cd4Hg99 (a = 2331.57(14) pm, R1 = 0.0465) is isotypic, whereas in the related zinc mercuride Ba20Zn5Hg99 (a = 2332.33(7) pm, R1 = 0.0436) one of the tetrahedra stars is filled by an extra zinc atom and is thus distorted into a [ZnHg8] cube. This extra zinc atom causes the small change in the compounds formula. The four crystallographically different Ba cations are coordinated by 17 or 18 Hg atoms. The mercury atoms themselves are surrounded by 10 to 13, in one case 16, Hg=Ba neighbors. The shortest Hg-Hg distances (dminHg-Hg = 285:8 pm) are found for the strong covalent bonds in the shell around the sodalite cages A and the cubes around Hg(13). The bonding modes (Hg-Hg distances and overall coordinations numbers) of the different Hg atoms of Ba20Hg103 are discussed in comparison with those in the more Hg-rich compounds BaHg6 and BaHg11. According to their crystal-chemical properties, the Hg atoms in Hg-rich mercurides can be classified into four different groups, from mainly covalent to polar intermetallic and pure metallic, to finally cationic centers Graphical Abstract Das neue komplexe Barium-Mercurid Ba20Hg103 und seine ternären Zink- und Cadmium-Varianten / The New Complex Barium Mercuride Ba20Hg103 and its Ternary Zinc and Cadmium Variants

Strontium-Metallide im Bereich des Schnitts SrIn4 – SrHg4 / Strontium Metallides along the Section SrIn4 – SrHg4

In a combined synthetic, X-ray single-crystal and bond-theoretical study the phase widths of SrIn4 and the related Sr3In11 upon a sucessive substitution of indium against the more electronpoor, more electronegative and only slightly smaller element mercury have been studied. Along the 1 : 4 section Sr(In1-xHgx)4 the monoclinic structure of SrIn4 ( EuIn4-type structure) is stable up to x =0.14(1) ( SrIn3.44Hg0.56: monoclinic, C2/m, a = 1208.3(6), b = 502:5(2), c = 997.7(6) pm, b = 115.16(3)°, Z = 4, R1 = 0.0324). Further increased mercury content results in a distinct stability region of the very common BaAl4 structure type (tetragonal, I4=mmm, Z = 2), which starts at x =0.241(7) ( SrIn3.04Hg0.96: a = 4694(2), c = 1246.4(7) pm, R1 = 0.0374) and reaches up to the fully ordered compound SrIn2Hg2 (x =0.5: a = 456.4(3), c = 1273.5(11) pm, R1 = 0.0572). Unexpectedly, in the small composition range from x=0.68(1) to 0.758(6) ( SrIn1.16Hg2.84: a=1178.5(4), b = 495.20(12), c = 1016.8(4) pm, b = 119.67(2)°, R1 = 0.0542; SrIn0.97Hg3.03: a = 1167.30(4), b = 495.32(2), c = 1018.50(3) pm, b = 119.657(2)°, R1 = 0.0426) the EuIn4 structure type exhibits a further small stability range. The structures of the two slightly different In- and Hg-rich variants of the EuIn4 type are described and compared, indicating the similarities to the KHg2 (layers of folded In=Hg ladders) and the BaAl4 structure type (flat square pyramids) as well as to the structure of elemental mercury (rhombohedra). From samples of an intermediate In=Hg ratio (e. g. x =0.55), the new 1 : 3 compound SrIn1.2Hg1.8 (monoclinic, C2=m, a = 1168.5(13), b = 497.0(4), c = 1471(2) pm, b = 92.07(10)°, Z = 8, R1 = 0.0818) is formed. It crystallizes in a new structure type, which - according to the compound’s composition - can be described as a stacking variant of the EuIn4 and the KHg2 structure type. In contrast to the wide stability ranges of the 1 : 4 compounds, only a very small substitution of In ranging up to only 6% of Hg is possible in the binary indide Sr3In11 ( Sr3In10.32(8)Hg0.68(8): La3Al11 structure type, orthorhombic, Immm, a = 487:6(2), b = 1140.2(5), c = 1421.1(7) pm, Z = 2, R1 = 0.0703). The formation, stability ranges and the In=Hg ‘coloring’ of the polyanions are discussed for all compounds taking into account geometric (radius ratios, molar volumes, Sr coordination polyhedra etc.) and electronic aspects, which have been evaluated using FP-LAPW band structure calculations. Graphical Abstract Strontium-Metallide im Bereich des Schnitts SrIn4 – SrHg4 / Strontium Metallides along the Section SrIn4 – SrHg4

Zink-reiche Erdalkalimetall-Verbindungen AZn5 und AZn11: Kristallstrukturen und chemische Bindung / Zinc-rich Alkaline Earth Compounds AZn5 and AZn11: Crystal Structures and Chemical Bonding

The zinc-rich compounds in the binary systems with the heavier alkaline earth elements CaZn11 and AZn5 (A = Ca, Sr, Ba) have been synthesized from melts of the elements. Their crystal structures, which were in principle known from very early powder or single crystal film experiments, have been refined on the basis of modern single crystal X-ray data. CaZn5 (hexagonal, space group P6/mmm, a = 538.99(2), c = 424.56(1) pm, Z = 1, R1 = 0.0144) crystallizes with the CaCu5 structure type and exhibits a small but distinct phase width Ca1−xZn5+2x up to a composition of Ca0.87Zn5.26 (a = 533.38(1), c = 430.04(1) pm, R1 = 0.0170) achieved through a gradual substitution of Ca by Zn2 dumbbells. The high-temperature form of SrZn5, which was prepared by quenching of melted samples, also adopts the ideal CaCu5 structure type (a = 554.1(2), c = 428.2(2) pm, R1 = 0.0314). The room temperature modification of SrZn5 (orthorhombic, space group Pnma, a = 1313.3(3), b = 529.91(10), c = 669.72(13) pm, Z = 4, R1 = 0.0349) forms a singular structure, whereas the Ba compound of corresponding composition (orthorhombic, space group Cmcm, a = 1078.3(7), b = 839.8(5), c = 532.0(3) pm, Z = 4, R1 = 0.0281) crystallizes with a third, also rather uncommon structure. For the compound CaZn11 (BaCd11 structure type; tetragonal, space group I41/amd, a = 1068.11(10), c = 682.81(7) pm, Z = 4, R1 = 0.0299) the originally proposed structure type was confirmed and also refined using single crystal data. The chemical bonding in all title compounds is analyzed using FP-LAPWband structure methods. Together with geometrical criteria and observed valence electron numbers of isotypic compounds, the results are used to compare and discuss the stability of the different structures of the intermetallic phases in the systems AZn5 and AM11 (M = Zn, Cd, Hg).

Sr3Al2Ge4, Ca10Al6Ge9 und Ca20Al6Ge13. Neue Aluminium-Germanide / Sr3Al2Ge4, Ca10Al6Ge9 and Ca20Al6Ge13. New Aluminium Germanides

In the ternary systems Ca-Al-Ge and Sr-Al-Ge three germanides with new structure types have been synthesized from stoichiometric ratios of the elements. Their crystal structures were determined using single crystal X-ray data. In the structure of Sr3Al2Ge4 (monoclinic, space group C2/m, a = 1267.6(4), b = 416.2(2), c = 887.4(3) pm, β = 110.37(2)°, Z = 2, R1 = 0.0354) Al-Ge sheets with Al in tetrahedral (i. e. Al−) and Ge in threefold ψ-tetrahedral (i. e. Ge−) coordination against Ge are present. Thus, the compound can be classified as an electron precise Zintl phase. This finding is verified by the result of a band structure calculation (within the FP-LAPW approach), that shows a distinct minimum of the total density of states at the Fermi level. The structure of Ca10Al6Ge9 (trigonal, space group R3̅m, a = 1398.45(14), c = 2107.4(3) pm, Z = 6, R1 = 0.0613) contains complicated sheets of trigonal planar building units [AlGe3] and [AlGe4] tetrahedra. The compound Ca20[Al3Ge6]2[Ge] (hexagonal, space group P63/m, a = 1600.9(2), c = 458.48(7) pm, Z = 1, R1 = 0.0282) shows two planar trimers of [AlGe3] triangles of formula [Al3Ge6] besides isolated Ge atoms (i. e. Ge4−). The overall electron count of the latter compounds, that contain trigonal planar coordinated Al atoms and considerable multiple bond character of the Al-Ge bonds, shows a very small deviation from the Zintl concept, comparable to the one observed in other aluminium-germanides like SrAlGe.

Alkaline-earth tri-mercurides AIIHg3 (AII=Ca, Sr, Ba): binary intermetallic compounds with a common and a new structure type

Abstract The alkaline-earth tri-mercurides AHg3 (A=Ca, Sr, Ba) were yielded from stoichiometric melts of the elements in pure phase (in the case of Sr with Sr11Hg54 as a by-product) and their structures were determined by means of single crystal X-ray data. As reported long ago from powder data, CaHg3 and SrHg3 crystallize in the Ni3Sn-type (P63/mmc, a=662.26(2)/689.39(3), c=501.64(2)/510.38(3) pm, Z=2, R1=0.0233/0.0306 for A=Ca/Sr). The structure consists of a hexagonal close packing of ordered layers AHg3 or a dense packing of anti-cuboctahedra [AHg12] (as cation coordination polyhedra, CCP) and [Hg6] octahedra fused via opposite faces to form columns along c. BaHg3 crystallizes in a unique structure type (P4/ncc, a=1193.04(3), c=958.02(5) pm, Z=12, R1=0.0461). It contains three crystallographically different Hg atoms, which form layers of distorted flat square pyramids. In contrast to the layers of the BaAl4-type, 15

Complex cubic metallides AM~6 (A=Ca, Sr; M=Zn, Cd, Hg). Synthesis, crystal chemistry and chemical bonding

{1 \over 5}

Sr(Hg1–xSnx)4: variations of the EuIn4-type structure

of the pyramids are missing. Due to the 45 degree rotation of adjacent layers, the connection between the layers is not a ‘apical-to-apical’ one like in BaAl4, but is established by ‘apical-to-basal’ bonds. Compared to the Ca and Sr compound, the CCPs of the two different Ba atoms, which are embedded between the pyramid layers, are increased to 12+4 and 14+2 (for Hg+Ba). For all title compounds and the Li phase LiHg3, which is isotypic to CaHg3, the electronic band structures were calculated within the framework of the FP-LAPW DFT method. Even though the compounds are metals and exhibit only very slight minima of the tDOS at the Fermi level, the electron transfer from the alkali/alkaline-earth element towards mercury is almost complete. Thus, Coulomb interactions and the optimized size and arrangement of the A CCPs, besides the flexible Hg–Hg bonding within the polyanion, determine the structure formation.

Barium-Triel-Mercuride BaMxHg4-x und Ba3MxHg11-x (M=Ga, In, Cd) / Barium Triel Mercurides BaMxHg4-x and Ba3MxHg11-x (M =Ga, In, Cd)

Abstract In a systematic synthetic, crystallographic and bond theoretical study, the stability ranges as well as the distribution of the isoelectronic late d-block elements Zn, Cd and Hg (M) in the polyanions of the YCd6-type phases (Ca/Sr)Cd6 have been investigated. Starting from Ca(Cd/Hg)6, 12−30% of the M atoms can be substituted by Zn, which gradually occupies the center of the empty cubes. In all ternary compounds, smaller/less electronegative Zn/Cd atoms occupy the disordered tetrahedra explaining the lack of the YCd6-type for pure mercurides. Along the section SrCd6-SrHg6, the ordered Eu4Cd25-type is formed (Sr4Cd16.1Hg8.9: cF1392, Fd3̅, a=3191.93(5) pm, R1=0.0404). Besides, two new complex cubic Ca phases appear at increased Zn proportion: Ca2Zn5.1Cd5.8, which exhibits a nearly complete site preference of Zn and Cd, crystallizes in the rare cubic Mg2Zn11-type structure (cP39−δ, Pm3̅, a=918.1(1) pm, R1=0.0349). In the Ca–Hg system, an increased Zn proportion yielded the new compound CaZn1.31Hg3.69 (cF480, F4̅3m, a=2145.43(9) pm, R1=0.0572), with a complex cubic structure closely related to Ba20Hg103. All structures, which are commonly described using nested polyhedra around high-symmetric sites, are alternatively described in accordance with the calculated electron densities and charge distribution: building blocks are face-sharing [M4] tetrahedra (star polyhedra such as TS, IS, OS), each with a cage-critical point in its center, and [M8] cubes (deformed TS), which are either empty, distorted or filled. The M element distribution in the anion is determined by size criteria and the difference in electronegativity, which induces a preferred formation of heteroatomic polar bonds.