Syntheses and Structures of Sc₂Nb_4–<i>x</i>Sn₅, YNb₆Sn₆, and ErNb₆Sn₅: Exploratory Studies in Ternary Rare-Earth Niobium Stannides

Three new rare-earth (RE) niobium stannides, namely, Sc₂Nb_4–<i>x</i>Sn₅ (<i>x</i> = 0.37, 0.52), YNb₆Sn₆, and ErNb₆Sn₅, have been obtained by reacting the mixture of corresponding pure elements at high temperature and structurally characterized by single-crystal X-ray diffraction studies. Sc₂Nb_4–<i>x</i>Sn₅ crystallizes in the orthorhombic space group <i>Ibam</i> (No. 72) and belongs to the V₆Si₅ type. Its structure features a three-dimensional (3D) network composed of two-dimensionally (2D) corrugated [Nb₂Sn₂] and [Nb₂Sn₃] layers interconnected via Nb–Sn bonds, forming one type of one-dimensional (1D) narrow tunnels along the <i>c</i> axis occupied by Sc atoms. YNb₆Sn₆ crystallizes in the hexagonal space group <i>P</i>6/<i>mmm</i> (No. 191) and adopts the HfFe₆Ge₆ type, and ErNb₆Sn₅ crystallizes in the trigonal space group <i>R</i>3̅<i>m</i> (No. 166) and belongs to the LiFe₆Ge₅ type. Their structures both feature 3D networks based on 2D [Nb₃Sn], [Sn₂], and [RESn₂] layers (RE = Y, Er). In YNb₆Sn₆, one type of [Nb₃Sn] layer is interconnected by [Sn₂] and [YSn₂] layers via Nb–Sn bonds to form a 3D network. However, in ErNb₆Sn₅, two types of [Nb₃Sn] layers are interlinked by [Sn₂] and [ErSn₂] layers via Nb–Sn bonds into a 3D framework. Electronic structure calculations and magnetic property measurements for “Sc₂Nb₄Sn₅” and YNb₆Sn₆ indicate that both compounds show semimetallic and temperature-independent diamagnetic behavior