Novel Corrugated In₉ Anionic Layer in Li₂Y₅In₉: Square Pyramidal In₅ Clusters Interconnected by Unusual Butterfly In₄ Clusters

The new ternary polar intermetallic phase, Li2Y5In9, was obtained by high-temperature solid-state reactions of the corresponding elements inwelded Ta tubes. Its crystal structure was established by a single-crystal X-ray diffraction study. Li2Y5In9 crystallizes in the tetragonal space group P4/nmm (No. 129) with cell parameters of a = b = 10.1242(4), c = 15.1091(10) Å and Z = 4. The structure of Li2Y5In9 features a two-dimensional corrugated anionic In9 layer composed of two types of square pyramidal In5 units and butterfly In4 units. There are two types of square pyramidal In5 units: one with normal In−In bonds and another one with greatly elongated In−In separations within its In4 square. Packing of these 2D In9 layers resulted in cavities and tunnels that are occupied by Y and Li atoms. Extended-Hückel tight-binding calculations indicate that Li2Y5In9 is metallic.