Synthesis and structure determination of seven ternary bismuthides: crystal chemistry of the RE Li 3 Bi 2 family ( RE = La–Nd, Sm, Gd, and Tb)

Zintl phases are renowned for their diverse crystal structures with rich structural chemistry and have recently exhibited some remarkable heat‐ and charge‐transport properties. The ternary bismuthides RE Li 3 Bi 2 ( RE = La–Nd, Sm, Gd, and Tb) (namely, lanthanum trilithium dibismuthide, LaLi 3 Bi 2 , cerium trilithium dibismuthide, CeLi 3 Bi 2 , praseodymium trilithium dibismuthide, PrLi 3 Bi 2 , neodymium trilithium dibismuthide, NdLi 3 Bi 2 , samarium trilithium dibismuthide, SmLi 3 Bi 2 , gadolinium trilithium dibismuthide, GdLi 3 Bi 2 , and terbium trilithium dibismuthide, TbLi 3 Bi 2 ) were synthesized by high‐temperature reactions of the elements in sealed Nb ampoules. Single‐crystal X‐ray diffraction analysis shows that all seven compounds are isostructural and crystallize in the LaLi 3 Sb 2 type structure in the trigonal space group P m 1 (Pearson symbol hP 6). The unit‐cell volumes decrease monotonically on moving from the La to the Tb compound, owing to the lanthanide contraction. The structure features a rare‐earth metal atom and one Li atom in a nearly perfect octahedral coordination by six Bi atoms. The second crystallographically unique Li atom is surrounded by four Bi atoms in a slightly distorted tetrahedral geometry. The atomic arrangements are best described as layered structures consisting of two‐dimensional layers of fused LiBi 4 tetrahedra and LiBi 6 octahedra, separated by rare‐earth metal cations. As such, these compounds are expected to be valance‐precise semiconductors, whose formulae can be represented as ( RE 3+ )(Li 1+ ) 3 (Bi 3− ) 2 .