No abstract

The title compound was synthesized by reaction of the elemental components in a corundum crucible at 1450 ºC, and subsequent crystal growth using the Bridgman technique. The crystal structure of Yb 2 Al 15 Pt 6 was determined from X-ray single crystal diffraction data: space group Cmcm, Pearson symbol oS92, a = 12.7969(1) Å, b = 7.38813(7) Å, c = 16.3605(2) Å, R F = 0.036 for 1455 observed structure factors and 65 variable parameters. The title compound crystallizes in a new type of structure, which represents an ordered variety of the Sc 1.2 Fe 4 Si 9.8 aristotype. The structure can be described as an (ABB) 2 stacking of two trigonal layers with compositions Yb 4 Al 6 (A) and Pt 6 Al 12 (B). The layers A are almost planar and consist of ytterbium atoms arranged at the apexes of condensed hexagons centered by triangular Al 3 units. The slabs B may be considered as distorted hexagonal close-packed, similar to three adjacent layers I− − − −Cd− − − −I of the structure type CdI 2 (Al− − − −Pt− − − −Al). The structural particularities of Yb 2 Al 15 Pt 6 are discussed in comparison with the related structures of Y 2 Ga 9 Co 3 , Tb 2 Ge 3 Pt 9 , Yb 2 Ga 9 Pd 3 and Er 4 Al 24 Pt 9. A real-space analysis of the chemical bonding with the electron-localizability approach showed that the crystal structure of Yb 2 Al 15 Pt 6 consists of an anionic Al− − − −Pt framework, with Yb cations embedded in cavities. The Al− − − −Pt interactions within the framework are covalent polar, whereas ionic bonding is observed between ytterbium and the framework.

Einschließlich Bor: Mit K7B7Si39 (siehe Struktur; große Kugeln: K, kleine Kugeln: Si, B) wurde erstmals eine Clathrat‐I‐Verbindung mit Bor hergestellt. Dieses Borosilicid hat mit 9.952(1) Å den kleinsten Gitterparameter aller intermetallischen Clathrat‐I‐Verbindungen. Seine Zusammensetzung entspricht dem Zintl‐Konzept.

Mg3−xGa1+xIr (x = 0.05) was synthesized by direct reaction of the elements in welded tantalum containers at 1200 °C and subsequent annealing at 500 °C for 30 days. Its crystal structure represents a new prototype and was determined by single-crystal technique as follows: space group P63/mcm, Pearson symbol hP90, Z = 18, a = 14.4970(3) Å, c = 8.8638(3) Å. The composition and atomic arrangement in Mg3GaIr do not follow the 8–N rule due to the lack of valence electrons. Based on chemical bonding analysis in positional space, it was shown that the title compound has a polycationic–polyanionic organization. In comparison with other known intermetallic substances with this kind of bonding pattern, both the polyanion and the polyanion are remarkably complex. Mg3−xGa1+xIr is an example of how the general organization of intermetallic substances (e.g., formation of polyanions and polycations) can be understood by extending the principles of 8–N compounds to electron-deficient materials with multi-atomic bonding.

Überraschende Eigenschaften hält der trigonal‐planare Komplex [Co(CN)3]6− bereit (siehe Strukturbild; Co rot, C grau, N grün, Erdalkalimetall‐Gegenionen gelb). Bindungslängen und Ladungen der CN‐Liganden variieren, und das Co‐Zentrum verfügt über eine geschlossenschalige (d10‐)Konfiguration.

The cover picture shows schematically the conditions for preparation and decomposition of strontium diazenides. The crystal structures of the diazenides, which were obtained as single‐phase products under high N2 pressure (up to 5500 bar), were determined by neutron diffraction. The background is provided by a section of the powder diffraction pattern of SrN2, and the coordination of the diazenide ions is shown top right. The N−N bond length in the diazenide ions is 122 pm in both compounds. Details of the preparation and characterization of the Sr diazenides are reported by G. Auffermann, Y. Prots, and R. Kniep on p. 547 ff.

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Das Titelbild zeigt schematisch die Synthese und Zersetzung von Strontiumdiazeniden. Die Kristallstrukturen der unter hohen N2‐Drücken (bis 5500 bar) phasenrein hergestellten Diazenide wurden durch Neutronenbeugung bestimmt. Im Bildhintergrund ist ein Ausschnitt des Beugungsdiagramms von SrN2, rechts oben die Koordination der Diazenid‐Ionen abgebildet. Der N‐N‐Abstand in den Diazenid‐Ionen beträgt in beiden Verbindungen 122 pm. Einzelheiten zur Synthese und Charakterisierung der Strontiumdiazenide sind in der Zuschrift von G. Auffermann, Y. Prots und R. Kniep auf S. 565 ff. zu finden.