Syntheses and crystal structures of Y7Co6Sn23 and RE5Co6Sn18 (RE = Sc, Ho)

Single crystals of Y7Co6Sn23 and RE5Co6Sn18 (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. Y7Co6Sn23 belongs to the Ho7Co6Sn23 type and crystallizes in the trigonal space group P-3m1 (No. 164) whereas RE5Co6Sn18 (RE = Sc, Ho) adopt the Tb5Rh6Sn18 type structure and crystallizes in the tetragonal space group I41/acd (No. 142). Their structures all feature a three-dimensional (3D) anionic framework based on [CoSn6] trigonal prisms. The structure of Y7Co6Sn23 is made from the ordinal stacking one type of 2D slab composed of the same [CoSn6] 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 RE5Co6Sn18 is built up from alternately stacking two types of 2D slabs, which are composed of different [CoSn6] 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 Y7Co6Sn23 and Sc5Co6Sn18 are metallic.