The isotypic intermetallic compounds R 3 Ru 4 Al 12 (R ϭ Y, Pr, Nd, Sm, GdϪTm) and R 3 Os 4 Al 12 (R ϭ Y, CeϪNd, Sm, GdϪTm) were prepared by reaction of the elemental components in an arc-melting furnace. Their crystal structure was determined from four-circle X-ray diffractometer data of Y 3 Ru 4 Al 12 : P6 3 /mmc, a ϭ 877.7(1) pm, c ϭ 952.3(1) pm, Z ϭ 2, R ϭ 0.028 for 361 structure factors and 28 variable parameters. It was also refined for Nd 3 Os 4 Al 12 (a ϭ 889.2(1) pm, c ϭ 960.3(1) pm, R ϭ 0.021 for 425 F values and 30 variables) and Gd 3 Os 4 Al 12 (a ϭ 884.7(1) pm, c ϭ 955.3(2) pm, R ϭ 0.020; 427 F values, 30 variables). The refinements of the occupancy parameters revealed mixed T/Al occupancy for some of the aluminum sites resulting in the compositions Y 3Inhaltsübersicht. Die isotypen intermetallischen Verbindungen R 3 Ru 4 Al 12 (R ϭ Y, Pr, Nd, Sm, GdϪTm) und R 3 Os 4 Al 12 (R ϭ Y, CeϪNd, Sm, GdϪTm) wurden durch Reaktion der Elemente im Lichtbogenofen hergestellt. Ihre Kristallstruktur wurde für Y 3 Ru 4 Al 12 mittels Röntgen-Vierkreis-Diffraktometerdaten bestimmt: P6 3 /mmc, a ϭ 877,7(1) pm, c ϭ 952,3(1) pm, Z ϭ 2, R ϭ 0,028 für 361 Strukturfaktoren und 28 variable Parameter. Sie wurde auch für Nd 3 Os 4 Al 12 (a ϭ 889,2(1) pm, c ϭ 960,3(1) pm, R ϭ 0,021 für 425 F-Werte und 30 Variable) und Gd 3 Os 4 Al 12 (a ϭ 884,7(1) pm, c ϭ 955,3(2) pm, R ϭ 0,020; 427 F-Werte, 30 Variable) verfeinert. Die Verfeinerung der Besetzungsparameter ergab gemischte T/Al-Besetzung für einige Aluminiumpositionen entsprechend der

Ternary rare earth platinum aluminides were prepared by arc‐melting of the elemental components followed by annealing in a high‐frequency furnace. Their crystal structure was determined for the yttrium compound from four‐circle X‐ray diffractometer data. It has hexagonal symmetry with a = 428.1(1) pm, c = 1638.3(3) pm, space group P63/mmc, and was refined to a conventional residual of R = 0.018 for 325 F values and 19 variable parameters. Of the five crystallographic positions, the yttrium position and one of the three aluminum positions show partial occupancies corresponding to the composition Y1.357(3)Pt4Al9.99(2) with the Pearson symbol hP20 — 4.65. These partially occupied sites are that close to each other that at best only one can be fully occupied. A model for an ordered distribution of occupied and unoccupied Y and Al sites requires a √3 larger a axis with the Pearson symbol hP20 — 4.67 for the subcell, very close to the experimental result. Corresponding superstructure reflections could be observed on an image‐plate single‐crystal diffractometer only in the form of diffuse streaks. The compound has the ideal composition Y2Pt6Al15 with Z = 2 for the superstructure. This corresponds to the formula Y1.33Pt4Al10 with Z = 1 for the subcell. The compounds A1.33Pt4Al10 with A = Gd, Tb, Dy, Ho, Er, Tm were found to be isotypic with that of the yttrium compound. This structure is closely related to or isotypic with, respectively, those of Yb2Fe4Si9, Sc1.2Fe4Si9.8, Ce1.2Pt4Ga9.8, Ce2Pt6Ga15, Tb0.67Ni2Ga5—xSix, RE0.67Ni2Ga5—xGex> (with RE = Y, Sm, Ho), and Gd0.67Pt2Al5, reported in earlier investigations. The new compound Zr1.00(1)Pt4Al10.22(3) has nearly the same hexagonal structure with a = 426.1(1) pm and c = 1622.8(3) pm. It was refined from four‐circle diffractometer data to a residual of R = 0.021 for 288 structure factors and 19 variable parameters.

No abstract

The 10 intermetallic compounds R(7+)(x)Os(12)Al(61+)(y) (R = Y, Nd, Sm, Gd-Tm) were prepared by arc-melting of the elemental components. They crystallize with a hexagonal structure very similar to that of Y(7.28)Re(12)Al(61.38). The structure was determined from four-circle diffractometer data of Y(7+)(x)Os(12)Al(61+)(y): P6(3)/mcm, a = 1301.5(2) pm, c = 903.0(2) pm, Z =1. Four atomic sites, all located on the 6(3) axis, show fractional occupancy, resulting in the composition Y(7.86(1))Os(12)Al(61.51(4)), corresponding to the Pearson symbol hP90-8.63. The structure may be viewed as consisting of alternating atomic layers of two kinds, although chemical bonding within and between the layers is of similar character as can be judged from the near-neighbor environments, where all of the 11 atomic sites have high coordination numbers. One kind of layers (A). is relatively loosely packed and contains the yttrium and some aluminum atoms. The other kind (B). consists of the osmium and the remaining aluminum atoms in a nearly hexagonal close-packed arrangement. These layers are stacked in the sequence ABAB. A similar building principle has recently been recognized for several other structures of ternary intermetallic compounds of rare earth and transition metals with a high content of aluminum or gallium, where the structures of CeOsGa(4), Ho(3)Ru(4)Ga(15), and Y(2)Pt(6)Al(15) are the most recent examples. This structural family is briefly reviewed. The cell volume of Yb(7+)(x)Os(12)Al(61+)(y) indicates a mixed or intermediate valence character +2/+3 for the ytterbium atoms of this compound.

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