Syntheses and crystal structures of Y 7Co 6Sn 23 and RE 5Co 6Sn 18 (RE = Sc, Ho)

Abstract

Single crystals of Y 7Co 6Sn 23 and RE 5Co 6Sn 18 (RE = Sc, Ho) have been obtained by solid-state reactions of the corresponding pure elements in welded tantalum tubes at high temperature. Their crystal structures have been established by single-crystal X-ray diffraction studies. Y 7Co 6Sn 23 belongs to the Ho 7Co 6Sn 23 type and crystallizes in the trigonal space group P-3 m1 (No. 164) whereas RE 5Co 6Sn 18 (RE = Sc, Ho) adopt the Tb 5Rh 6Sn 18 type structure and crystallizes in the tetragonal space group I4 1/ acd (No. 142). Their structures all feature a three-dimensional (3D) anionic framework based on [CoSn 6] trigonal prisms. The structure of Y 7Co 6Sn 23 is made from the ordinal stacking one type of 2D slab composed of the same [CoSn 6] trigonal prisms via corner-sharing, forming two types of narrow tunnels along the c-axis, which are occupied by Y or residual Sn atoms. The 3D structure of RE 5Co 6Sn 18 is built up from alternately stacking two types of 2D slabs, which are composed of different [CoSn 6] trigonal prisms via corner-sharing and Sn–Sn bonds, respectively. The RE and residual Sn atoms are located in the spacers of the 3D framework. Band structure calculations indicate that Y 7Co 6Sn 23 and Sc 5Co 6Sn 18 are metallic.