Thulium nickel/lithium distannide, TmNi(1−x)Li(x)Sn(2) (x = 0.035)

The quaternary thulium nickel/lithium distannide, TmNi(1−x)Li(x)Sn(2) (x = 0.035), crystallizes in the ortho­rhom­bic LuNiSn(2) structure type. The asymmetric unit contains three Tm sites, six Sn sites, two Ni sites and one Ni/Li site [relative occupancies = 0.895 (8):0.185 (8)]. Site symmetries are .m. for all atoms. The 17-, 18- and 19-vertex distorted pseudo-Frank–Kasper polyhedra are typical for all Tm atoms. Four Sn atoms are enclosed in a 12-vertex deformed cubo­octa­hedron, and another Sn atom is enclosed in a penta­gonal prism with three added atoms. A tricapped trigonal prism is typical for a further Sn atom. The coordination number for all Ni atoms and Ni/Li statistical mixtures is 12 (fourcapped trigonal prism [Ni/LiTm(5)Sn(5)]). Tm atoms form the base of a prism and Ni/Li atoms are at the centres of the side faces of an [SnTm(6)Ni/Li(3)] prism. These isolated prisms are implemented into three-dimensional-nets built out of Sn atoms. Electronic structure calculations using TB-LMTO-ASA suggest that the Tm and Ni/Li atoms form positively charged n[TmNi/Li](m+) polycations which compensate the negative charge of 2n[Sn](m−) polyanions. Analysis of the inter­atomic distances and electronic structure calculations indicate the dominance of a metallic type of bonding.