Pentaterbium lithium tristannide, Tb5LiSn3

The new ternary phase pentaterbium lithium tristannide, Tb5LiSn3, crystallizes in the hexagonal Hf5CuSn3 structure type, which is a ‘filled’ version of the binary RE 5Sn3 phases (Mn5Si3-type) (RE is rare earth). The asymmetric unit contains two Tb sites (site symmetries 3.2 and m2m), one Li site (site symmetry .m) and one Sn site (site symmetry m2m). The 14-vertex Frank–Kasper polyhedra are typical for Li and Tb atoms. The environment of the Sn atom is a pseudo-Frank–Kasper polyhedron with a coordination number of 13 for the tin atom. One of the Tb atoms is enclosed in a 17-vertex polyhedron. The metallic type of bonding was indicated by an analysis of the interatomic distances.

The new ternary phase pentaterbium lithium tristannide, Tb 5 LiSn 3 , crystallizes in the hexagonal Hf 5 CuSn 3 structure type, which is a 'filled' version of the binary RE 5 Sn 3 phases (Mn 5 Si 3 -type) (RE is rare earth). The asymmetric unit contains two Tb sites (site symmetries 3.2 and m2m), one Li site (site symmetry 3.m) and one Sn site (site symmetry m2m). The 14-vertex Frank-Kasper polyhedra are typical for Li and Tb atoms. The environment of the Sn atom is a pseudo-Frank-Kasper polyhedron with a coordination number of 13 for the tin atom. One of the Tb atoms is enclosed in a 17-vertex polyhedron. The metallic type of bonding was indicated by an analysis of the interatomic distances.

Crystal data
Financial support from the Ministry of Education and Science, Youth and Sport of Ukraine (N 0111U001089) is gratefully acknowledged.

Comment
The RE 5 TM 3 (RE -rare earth, T -Cu, Ag and M -Sn, Pb) ternary stannides crystallize in a hexagonal Hf 5 CuSn 3 (superstructure to Ti 5 Ga 4 -type) with space group P6 3 /mcm (Rieger and Parthé, 1965). These intermetallic compounds are characterized by two different sites for the RE atoms located at 4 d and 6 g, respectively. The Sn or Pb atoms are located at the next 6 g site and the transitions atoms occupy 2 b site.The RE 5 TM 3 intermetallics are 'filled' version of the binary RE 5 M 3 phases which crystallize in Mn 5 Si 3 structure type. It is also possible, that the transition metals fill the octahedral voids.
For the Ce based compounds, Ce 5 TM 3 , investigated by (Tran et al., 2008) are found multiple magnetic phase transitions at low temperatures and discussed the role of f-spd hybridization on the evolution of heavy-fermion behaviour.
We detected the new ternary compound during the systematic study of ternary alloys of Tb-Li-Sn system from the concentration region with low content of lithium. The powder diffraction pattern of this compound is similar to the powder pattern of the RE 5 Sn 3 (RE -rare-earth metals) binary phases, but has some differences. So we decided to further study this phase using single-crystal method. Obtained single-crystal data show that the title compound crystallizes with the hexagonal space group P6 3 /mcm as a Hf 5 CuSn 3 type. The projection of the unit cell and coordination polyhedra of the atoms are shown In the title compound lithium atoms occupy the same crystallographic position that the atoms of transition metal in the original structure type. The same was observed previously when we studied RELiSn 2 compounds with the CeNiSi 2 structure type (Pavlyuk et al., 1989), RELiGe with the ZrNiAl type (Pavlyuk et al., 1991 andBodak, 1992a), RE 3 Li 2 Ge 3 with Hf 3 Ni 2 Si 3 type (Pavlyuk & Bodak, 1992b), solid solutions RLi x Cu 2 -x Si 2 and RLi x Cu 2 -x Ge 2 (Pavlyuk et al., 1993).