Yb3Cu6Sn5, Yb5Cu11Sn8 and Yb3Cu8Sn4: crystal structure of three ordered compounds

Yb3Cu6Sn5, Yb5Cu11Sn8 and Yb3Cu8Sn4 compounds were prepared in sealed Ta crucibles by induction melting and subsequent annealing. The crystal structures of Yb3Cu6Sn5 and Yb5Cu11Sn8 were determined from single crystal diffractometer data: Yb3Cu6Sn5, isotypic with Dy3Co6Sn5, orthorhombic, Immm, oI28, a=4.365(1) A, b=9.834(3) A, c=12.827(3) A, Z=2, R=0.019, 490 independent reflections, 28 parameters; Yb5Cu11Sn8 with its own structure, orthorhombic, Pmmn, oP48, a=4.4267(6) A, b=22.657(8) A, c=9.321(4) A, Z=2, R=0.047, 1553 independent reflections, 78 parameters. Both compounds belong to the BaAl4-derived defective structures, and are closely related to Ce3Pd6Sb5 (oP28, Pmmn). The crystal structure of Yb3Cu8Sn4, isotypic with Nd3Co8Sn4, was refined from powder data by the Rietveld method: hexagonal, P63mc, hP30, a=9.080(1) A, c=7.685(1) A, Z=2, Rwp=0.040. It is an ordered substitution derivative of the BaLi4 type (hP30, P63/mmc). All compounds show strong Cu-Sn bonds with a length reaching 2.553(3) A in Yb5Cu11Sn8