Y4Ir9Si5, a new substitution variant of the Ce2Ni7 type and isotypes of other members of the R2+nT3+3nM1+2n structure series

Y4Ir9+xSi5-x, x=0.12(2), Mr=2226 for Y4Ir9Si5, hP36, P63/mmc, a=5.4894(2), c=22.6054(9) A, V=589.93(6) A3, Z=2, Dx=12.53 Mg m-3 (Y4Ir9Si5), Mo Kα, λ=0.71073 A, μ=127.4 mm-1, F(000)=1838, T=293 K, wR=0.061 for 308 independent reflections. The Y4Ir9Si5 type is a site-occupation variant of the Ce2Ni7 type. It is a new member (n=2) of the hexagonal branch of the structure series R2+nT3+3nM1+2n, grouping types where ternary Laves-type slabs are intergrown with ternary CeCo3B2-type slabs. ErRh2Si, ErRh2Ge, YIr2Si and YRh2Ge were found to crystallize with the YRh2Si type (site-occupation variant of the CeNi3 type), Er4Rh9Ge5 and Y4Rh9Ge5 with the Y4Rh9Si5 type (site-occupation variant of the Gd2Co7 type). The former structure type belongs to the hexagonal and the latter to the rhombohedral branch of the same structure series. (orig.)